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db cool? remote thermal controller and fan controller adt7460 rev. c in fo rmation furn ished by an alog d e v i c e s is believed to be accurate and reliable. how e ver, n o resp on sibili ty is assume d b y a n alog de vices fo r its use, nor for an y i n fri n geme nt s of p a t e nt s or ot h e r ri ght s o f th ird parties th at may result fro m its use . s p ecificatio n s subj ec t to ch an g e witho u t n o tice. no licen s e is g r an te d by implicati o n or ot herwi s e u n der a n y p a t e nt or p a t e nt ri ghts of analog de v i ces. trademarks an d registered tra d ema r ks are the prop erty o f their respective ow ners. one technolog y way, p.o . box 9106, norwood, ma 02062-9106, u.s.a. t e l: 781. 329. 4 700 www.analog.com fax: 781. 461. 31 13 ? 2005 analog de vices, i n c. al l r i ght s r e ser v ed . features controls and m o nitors up to 4 fan speeds 1 on-chip and 2 remote tempe r ature sensors dynamic t min control mode optimizes sys t e m acoustics intelligently automatic fan speed control mo de controls system cooling based on meas ured t e mperat ure enhanced acoustic mode dra m atically r e duc e s user perception of changing fan speeds thermal protection feature via therm ou tpu t monitors performance impact of intel ? pentium ? 4 processor thermal control circuit via therm input 2-wire and 3-w i re fan spee d m easurement limit comparis on of all monitored values meets smbus 2 . 0 electrical sp ecifications (ful ly smbus 1.1-compliant) applic ati o ns low acoustic n o ise pcs networking an d telecommuni cations equipment general description the adt7460 1 db c o o l co n t rol l er is a t h er ma l m o ni t o r an d m u l t i p le p w m fa n co n t r o l l er fo r n o is e- s e n s i t i v e a p pli c a t ion s r e q u ir in g ac t i v e sy st em co oli n g. i t ca n m o n i t o r t h e t e m p era t ur e of up to t w o re mot e s e n s or d i o d e s plu s it s ow n i n te r n a l te m p - era t ur e . i t ca n m e as ur e an d con t r o l t h e s p e e d o f u p t o fo ur fa n s s o tha t t h ey o p era t e a t t h e lo w e st p o s s i b l e s p ee d f o r minim u m a c ou st i c noi s e. t h e a u tom a t i c f a n sp e e d c o n t ro l l o op opt i m i z e s fa n sp e e d fo r a g i ven te m p er a t ur e. a uniq u e dy na mic t min co n t r o l m o de e n a b les t h e sys t e m t h er mals/acous tics t o be in te l l ig e n t l y mana g e d . th e ef fe c t i v e n es s o f t h e sys t em s t h er ma l s o l u t i o n ca n b e m o n i to r e d using t h e therm in p u t . th e adt7460 als o p r o v ides cr i t ic al th er mal p r o t ec t i o n t o t h e sys t em b y usin g t h e b i dir e c t io nal therm pi n a s an ou tput t o p r ev e n t s y s t em o r co m p o n en t o v e r h e a t i n g. func tio n a l block di agram 03228- 001 input signal conditioning and analog multiplexer gnd serial bus interface scl sda value and limit registers limit comparators interrupt status registers band gap temp sensor v cc t o adt 7460 address pointer register pwm configuration registers interrupt masking v cc d1+ d1 ? d2+ d2 ? +2.5v in thermal protection performance monitoring pwm registers and controllers pwm1 pwm2 pwm3 acoustic enhancement control band gap reference 10-bit adc adt7460 automatic fan speed control dynamic t min control fan speed counter tach1 tach2 tach3 tach4 therm smbalert smbus address selection addr select addr_en fi g u r e 1 . 1 p r ot ec t e d b y u . s. p a t e n t nos. 6,188,189; 6,169,442; 6, 097,239; 5,982,221; and 5,867,012. o ther pa t e n t s pending .
adt7460 rev. c | page 2 of 52 table of contents specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 5 thermal characteristics .............................................................. 5 esd caution .................................................................................. 5 pin configuration and function descriptions ............................. 6 typical performance characteristics ............................................. 7 product description ......................................................................... 9 measurement inputs .................................................................... 9 sequential measurement ............................................................. 9 recommended implementation ................................................. 9 adt7460 address selection ..................................................... 10 internal registers of the adt7460 .......................................... 10 theory of operation ...................................................................... 11 serial bus interface ..................................................................... 11 voltage measurement input ...................................................... 15 additional adc functions for voltage measurements ........ 17 temperature measurement system .......................................... 17 additional adc functions for temperature measurement 19 limits, status registers, and interrupts ................................... 20 status registers ........................................................................... 21 handling smbalert interrupts ............................................. 22 therm timer ........................................................................... 24 fan drive using pwm control ............................................... 27 operating from 3.3 v standby ................................................. 33 xnor tree test mode .............................................................. 33 power-on default ...................................................................... 33 adt7460 register summary ........................................................ 34 outline dimensions ....................................................................... 51 ordering guide .......................................................................... 51 revision history 3/05rev. b to rev. c updated format.................................................................. universa l changes to absolute maximum ratings table..............................5 changes to adt7460 register map summary section .............34 updated ordering guide................................................................51 9/03rev. a to rev. b changed xor tree test mo de to xnor ............................ universal changes to specifications............................................................. 2 changes to tpc 7.................................................................................... 7 6/03rev. 0 to rev. a updated ordering ............................................................................4 updated the serial bus interface section................................9 added the to assign therm functionality to a pin 9 section ....21 added the therm as an inpu t section .............................................21 renamed the therm input section to therm timer ....................21 renumbered the figure s after fig ure 25.............................................22 updated step 1 in the configuring the desired therm behavior section........................................................................................................2 updated the fan speed control section ............................................28 added the power-on default section .....................................29 updated ta ble iv ..................................................................................30 updated tabl e xviii ............................................................................38 updated ta ble xx .................................................................................40 updated ta ble xxxv ...........................................................................46 updated outline dimensions ...................................................49
adt7460 rev. c | page 3 of 52 specifications t a = t min to t max , v cc = v min to v max , unless otherwise noted. table 1. parameter 1 , , 2 3 min typ 4 max unit test conditions/comments power supply supply voltage 3.0 5.0 5.5 v supply current, i cc 3 ma interface inactive, adc active 20 a standby mode temperature-to-digital converter local sensor accuracy 1.5 c 0c t a 70c 3 c ?40c t a +120c resolution 0.25 c remote diode sensor accuracy 1.5 c 0c t a 70c; 0c t d 120c 2.5 c 0c t a 105c; 0c t d 120c 3 c 0c t a 120c; 0c t d 120c resolution 0.25 c remote sensor source current 180 a high level 11 a low level analog-to-digital converter (including mux and attenuators) total unadjusted error, tue 1.5 % differential nonlinearity, dnl 1 lsb 8 bits power supply sensitivity 0.1 %/v conversion time (voltage input) 11.38 13 ms averaging enabled conversion time (local temperatur e) 12.09 13.50 ms averaging enabled conversion time (remote temperature) 25.59 28 ms averaging enabled total monitoring cycle time 120.17 134. 50 ms averaging enabled (incl. delay 5 ) 13.51 15 ms averaging disabled input resistance 80 140 200 k? fan rpm-to-digital converter accuracy 7 % 0c t a 70c 11 % 0c t a 105c 13 % ?40c t a +120c full-scale count 65,535 nominal input rpm 109 rpm fan count = 0xbfff 329 rpm fan count = 0x3fff 5000 rpm fan count = 0x0438 10000 rpm fan count = 0x021c internal clock frequency 82.8 90.0 97.2 khz open-drain digital outputs, pwm1Cpwm3, xto current sink, i ol 8.0 ma output low voltage, v ol 0.4 v i out = ?8.0 ma, v cc = 3.3 v high level output current, i oh 0.1 1 a v out = v cc open-drain serial data bus output (sda) output low voltage, v ol 0.4 v i out = ?4.0 ma, v cc = 3.3 v high level output current, i oh 0.1 1 a v out = v cc smbus digital inputs (scl, sda) input high voltage, v ih 2.0 v input low voltage, v il 0.4 v hysteresis 500 mv
adt7460 r e v. c | pa ge 4 o f 5 2 parameter 1 , 2 , 3 m i n t y p 4 m a x u n i t test condition s / c o m m e n t s digital inpu t logic level s ( t ach inpu ts) input high volt age, v ih 2 . 0 v 5.5 v maximum input voltage input low voltage, v il + 0 . 8 v ? 0 . 3 v m i n i m u m i n p u t v o l t a g e h y s t e r e s i s 0 . 5 v p - p digital inpu t logic level s ( ther m ) input high volt age, v ih 1 . 7 v input low voltage, v il 0 . 8 v digital inpu t curren t input high curr ent, i ih ? 1 a v in = v cc input low current, i il + 1 a v in = 0 input capacitance, c in 5 p f serial bus timi ng 6 clock fre quenc y , f sclk 400 khz see figure 2 glitch immunity, t sw 5 0 n s bus free time, t buf 1.3 s see figure 2 start setup time, t su ;st a 0.6 s see figure 2 start hold time, t hd;sta 0.6 s see figure 2 scl low time, t low 1.3 s see figure 2 scl high time, t high 0.6 s see figure 2 scl, sda rise ti me, t r 300 ns see figure 2 scl, sda fall time, t f 300 s see figure 2 data setup tim e , t su ;dat 100 ns see figure 2 detect clock lo w t imeout, t time o u t 15 35 ms can be optio nal l y disabled 3 timing s p ecif ications are tes t ed at logi c l e v e ls of v il = 0.8 v f o r a fa l l i n g e d ge a n d a t v ih = 2.0 v fo r a ri si n g edg e . 4 typi ca ls a r e a t t a = 25c a n d repre s en t t h e m o st li kel y pa ra m e t r i c n o rm . 5 the de l a y is the time be twe e n the round ro bin f i nis h ing o n e se t of me a s ureme nts and s t arting the ne xt. 6 guarante e d by d e sign, no t pro d uctio n te s t ed . 1 a l l volt a g e s a r e m e a s ured wi t h resp ect t o gn d , un le ss ot h e rwi s e speci f i e d. 2 lo gic inputs acce p t input high vo l t age s up to v ma x even wh en t h e device is operat in g down t o v min . scl sd a ps sp t buf t hd; sta t hd; dat t su; dat t f t r t low t su; sta t high t hd; sta t su; sto 03228-002 f i gure 2. s e r i al bus t i ming d i agr a m
adt7460 r e v. c | pa ge 5 o f 5 2 absolute maximum ratings table 2. p a r a m e t e r r a t i n g positive supply voltage (v cc ) 6 . 5 v voltage on any other input or output pin ?0.3 v to +6.5 v input current at any pin 5 ma package input current 20 ma maximum junction temperature (t j max) 150c storage temperature range ?65c to +150c lead temperature, soldering ir reflow peak temperature 220c ir reflow peak temperature for pb free 260c lead temperature (soldering 10 s) 300c esd rating 1500 v s t r e s s es a b o v e t h os e list e d u nde r a b s o l u te m a xim u m r a t i n g s ma y ca us e p e r m a n e n t dama ge to t h e de vi ce. t h is is a st r e ss r a t i ng on ly ; f u n c t i on a l op e r at i o n of t h e d e v i c e a t t h e s e or an y o t h e r con d i t ions a b o v e t h o s e i ndic a te d i n t h e op er a t io na l s e c t io n o f t h is sp e c if ic a t io n is no t im pl ie d . e x p o sur e t o a b s o l u te max i m u m r a t i ng co ndi t i on s fo r ex tende d p e r i o d s ma y a f fe c t de vice rel i a b i l i t y . thermal c h aracteristics 16-l e ad qso p p a c k a g e: ja = 150c/w jc = 39c/w esd caution esd (electrostatic discharge) sensitive device. electrosta tic char ges as high as 4000 v readily ac cumulate on the human body and test eq uipment and c a n d i scharge wit h out d e tection. although th is product features proprietary esd protection circ uitry, permanent dama ge may occur on devices subjected to high energy electrostatic di scharge s . ther efore, pro p er esd precautions are rec o m m ended to avoid performan c e degradation or l o ss of functiona l ity.
adt7460 r e v. c | pa ge 6 o f 5 2 pin conf iguration and fu nction descriptions 03228-003 adt7460 top view (not to scale) 1 2 15 p w m 1 / x t o 3 4 5 16 14 13 12 scl gnd v cc tach3 2 / s m b a l e r t sda +2.5v in /smbalert 6 11 10 tach1 7 tach2 8 9 pwm3/address enable p w m d1+ d1? d2+ d2? tach4/address select/therm f i gure 3. pin config ur ation t a ble 3 . p t i on d e s c ri pt pin no. mnemonic i n f u n c i o ns description 1 scl digital input (open drain). smbus seri al c l ock i n put. requires smbus pull-up. 2 gnd 4 6 0 . g r o u n d p i n f o r t h e a d t 7 3 v cc power supply. c a n be po wered by 3.3 v stand b y if monitoring in low p o wer sta t es is required . v cc i s a l s o monitored through this pin. the adt7460 can also b e p o w e r e d from a 5 v sup p ly. setting bit 7 of configuration register 1 (reg. 0 x 40) rescale s the v cc input atte n u a t o r s t o c o r r e c t l y m e a s u r e a 5 v s u p p l y . 4 tach3 r e s p e e d o f f a n 3 . c a n b e r e c o nfigured as an digital input (open drain). fan tachometer input to me a s u analog input (ai n 3) to measure the speed of 2-wire fans. 5 pwm2 u t p u t ( open drain). req u ires 10 k? typical pu l l -up. puls e-wid t h mod u lated output to control smbaler t d i g i t a l o fan 2 speed. digital output ( open drain). this p i n m a y b e r e c o nfigured as an smbaler t interrupt outpu t to signal out-of-limit con d itions. 6 tach1 r e s p e e d o f f a n 1 . c a n b e r e c o nfigured as an digital input (open drain). fan tachometer input to me a s u analog input (ai n 1) to measure the speed of 2-wire fans. 7 tach2 digital input (open drain). fan tachometer input to me asure speed of fan 2. can be reco nfigured as an analog input (ai n 2) to measure the speed of 2-wire fans. 8 pwm3 y p i c a l digital i/ o (open drain). pulse-width modulated output to control fan 3/4 spe e d . r e q u i r e s 1 0 k ? t pull-up. a d d r e s s enable if pulled low on power-up, thi s place s t h e a d t 7 4 6 0 into address select mode, and the state of p i n 9 determines the adt7460s slave address. 9 t a c h 4 p u t t o m e asure speed of fan 4. can be reco nfigured as an digital input (open drain). fan t a c h o m e t e r i n analog input (ai n 4) to measure the speed of 2-wire fans. address s elec t if in address select mode, th is pin determines the smbus device address. ther m alternatively, the pin may be re configured as a bidirectiona l ther m p i n . c a n b e u s e d t o t i m e a n d m o n i t assertio ns on th e o r ther m input. for exa m ple, ca n be co nnected to the prochot output of intels pentium 4 proces sor or to t h e output of a trip point temper a ture sensor. can be used as an output to signal overtemperatur e conditions. 10 d2? c a t h o d e c o n n e ction to second thermal diode. 11 d2+ anode connecti o n to second thermal diode. 1 2 d1? cathode connection to first thermal diode. 1 3 d1+ anode connecti o n to first thermal diode. 14 +2.5v in analog input. monitors 2.5 v suppl y, typically a chipset voltage. smbaler t digital output ( open drain). this pin may be rec o nfigured as an smbaler t interrupt outpu t to signal out-of-limit con d itions. 15 pwm1/xto digital output ( open drain). pulse-wi dth modulated output to control fan 1 spe e d. requires 10 k? typical pull-up. 16 sda digital i/o ( ope n drain) . sm bus bid i rectiona l ser i al d a ta. requires sm bus pull-up .
adt7460 r e v. c | pa ge 7 o f 5 2 typical perf orm ance cha r acte ristics leakage resistance (m ? ) re mote te mp e rature e rror ( c) 15 10 ?2 0 1 3.3 100.0 10.0 30.0 0 ?5 ?1 0 ?1 5 5 dx p t o g nd dxp to v cc (3.3v) 03228-004 f i g u re 4. r e mo te t e mpe r at u r e e r ror v s . l e ak ag e r e s i s t an ce dxp?dxn capacitance (nf) re mote te mp e rature e rror (c) 3 1 0 ?3 ?6 ?9 ?12 ?15 ? 1 8 ?21 ? 2 4 ?27 2.2 3.3 4.7 10.0 22.0 47.0 ? 3 0 ?33 ?36 remote temperature error (c) 03228-005 f i g u r e 5. r e mo te t e mpe r atu r e e r ror v s . capa cit a nc e bet w een d+ and d? temperature ( c) re mote te mp e rature e rror ( c) 3 ?4 0 2 1 0 ?1 ?2 ?3 10 60 110 ?3 sigma +3 sigma low limit high limit 03228-006 temperature (c) local te mp e rature e rror ( c) ?3 ?40 1 0 110 60 1 0 ?2 ?1 3 2 low limit high limit ? 3 sigma +3 sigma 03228-007 f i gure 7. l o c a l t e m p er atu r e e rror v s . ac tua l t e mper ature frequency (hz) re mote te mp e rature e rror (c) 14 12 ?2 100k 550k 50m 5m 6 4 0 2 10 8 100mv 250mv 03228-008 f i g u r e 8. r e mo te t e mpe r atu r e e r ror v s . p o wer su p p ly no is e f r eque nc y rror ( c) 12.5 10.0 ?5.0 100k 550k 50m frequency (hz) local te mp e rature 5m 5.0 2.5 ?2.5 0 7.5 100mv e 250mv 03228-009 f i gure 9. l o c a l t e m p er atu r e e rror v s . p o w e r sup p l y n o is e f r equ e nc y f i gure 6. r e mo te t e mpe r atu r e e r ror v s . ac tual t e mpe r atu r e
adt7460 r e v. c | pa ge 8 o f 5 2 1.90 1.85 1.80 1.75 1.70 1.65 1.60 1.55 1.50 1.45 1.40 2.5 2.6 3.0 3.4 3.8 4.2 4.6 5.0 5.4 5.5 s u pp l y vo lt a g e ( v) suppl y current (m a) 03228-010 f i gure 10. sup p l y current v s . sup p ly v o ltag e frequency (hz) re mote te mp e rature e rror (c) 16 60k 14 12 10 8 6 4 2 0 ?2 110k 1m 10m 50m 10mv 20mv 03228-011 f i gure 11. r e m o te t e m p er ature e r r o r v s . d i ffer e nti a l mo de n o ise f r equenc y 10k frequency (hz) re mote te mp e rature e rror ( c) 40 35 30 25 20 15 10 5 0 ?5 ?10 100k 1m 10m 20mv 40mv 100mv 03228-012 f i gure 12. r e m o te t e m p er ature e r r o r v s . com m on-m ode no ise f r equ e nc y
adt7460 r e v. c | pa ge 9 o f 5 2 product description the adt7460 is a t h er mal m o ni t o r an d m u l t i p le fa n co n t r o l l er fo r a n y sy stem r e q u ir in g m o ni to r i n g a nd co oli n g. t h e d e v i ce co mm unic a t es wi t h t h e sys t em v i a a s e r i al s y st e m m a na g e m e n t b u s (s mb us). th e s e r i al b u s con t r o l l er has a n o p tio n al addr ess line fo r de v i ce s e le c t ion (pin 9), a s e r i a l da t a li ne fo r r e adin g a nd wr i t i n g ad d r ess e s a nd da t a (pin 16), a nd an in p u t li n e fo r th e s e r i al c l o c k (p in 1). al l con t r o l a n d p r og ra mming f u n c tion s o f t h e a d t746 0 a r e p e r f o r m e d o v er t h e s e r i al b u s. i n addi t i o n , tw o o f t h e p i ns ca n b e r e co nf ig ur e d as a n sm b a l e r t output to indi ca t e o u t - o f - l imi t con d i t io n s . measurement inputs the de v i ce has t h r e e m e as ur e m en t i n p u ts, on e fo r v o l t a g e a nd t w o f o r t e m p era t ur e . i t ca n also m e as ur e i t s o w n s u p p l y v o l t a g e a nd can m e as ure a m b i e n t tem p era t ur e w i t h i t s o n -chi p t e m p era t ur e s e ns o r . pin 14 is a n a n a l og in p u t w i t h an o n -chi p a t t e n u a t o r and is co nf igur e d to mo ni to r 2.5 v . p o w e r is s u p p lie d t o t h e chi p v i a p i n 3, an d t h e s y s t em als o mon i tors v cc thr o ug h this p i n. i n pcs, t h is p i n is n o r m al l y co nn e c te d to a 3.3 v st andb y su p p ly . this pin ca n, h o we ver , b e co nn e c te d to a 5 v su p p ly a nd m o n i to r i t w i t h o u t o v er r a n g ing . re m o te t e m p er a t ur e s e n s i n g is p r o v ide d b y t h e d1 a nd d2 i n put s , to w h i c h di o d e - c o n n e c te d, e x te r n a l t e m p e r a t u r e - s e ns i n g tra n sis t o r s, s u ch as a 2 n 3904 o r cpu t h er mal dio d e , ma y be co nn e c te d. t h e a d c also accep t s i n p u t f r o m a n o n - c hi p b a n d ga p t e m p era t ur e s e ns o r , w h ich m o ni t o rs sys t em am b i en t te m p e r a t u r e. sequential measurement w h en t h e ad t7460 m o ni t o r i ng s e q u en ce is st a r t e d , i t c y c l es s e q u en t i al l y t h r o ug h t h e m e as u r em e n t o f 2.5 v in p u t an d t h e t e m p era t ur e s e ns o r s. m e as ur e d val u es f r o m t h e s e in p u ts a r e s t o r e d i n va l u e r e g i s t ers. th e s e c a n b e r e ad ou t o v er t h e s e r i al b u s o r ca n be co m p a r ed w i t h p r ogra m m ed li mi t s s t o r ed i n t h e l i m i t re g i ste r s . t h e re su lt s of o u t - of - l i m it c o m p ar i s ons are store d i n t h e s t a t u s re g i ste r s , w h ich c a n b e re a d o v e r t h e s e r i a l bu s to f l ag out - of - l i m it c o nd it i o ns . recommended imple m entation c o nf igur in g t h e ad t7460 as in f i gur e 13 al lo ws th e syst em s desig n er t h e fol l o w in g fe a t ur es: ? t w o p w m o u t p u t s f o r fa n co n t r o l o f u p t o thr e e fa n s (t h e f r on t and re ar c h a s s i s f a ns are c o n n e c te d i n p a r a l l el ) . ? thr e e t a ch fan sp e e d m e a s ur em e n t in pu ts. ? v cc m e as ur e d in t e r n al l y thr o u g h p i n 3. ? c p u te m p e r a t u r e me a s u r e d u s i n g r e mote 1 te m p e r a t u r e cha nnel. ? a m b i en t t e m p era t ur e m e as ur ed th r o ug h r e m o t e 2 t e m p era t ur e cha nne l . ? bidire c t ion a l therm p i n. al lo ws i n te l p e n t i u m 4 pro c h o t m o n i to r i n g and can f u nc t i o n as a n o v er t e m p er a t ure therm output . ? sm b a l e r t syst em in ter r u p t o u t p u t . ich tach2 d1+ d1? d2+ d2? tach1 p ambient temperature pwm3 t a c h 3 gnd adt7460 scl smbalert sda w m 1 therm prochot front chassis 3228- 013 fan rear chassis fan f i gure 13. r e c o m m e nded i m p l e m ent a tion
adt7460 rev. c | page 10 of 52 dres -functio adt7460 ad s selection n pwm pin 8 is the dual 3/ address enable pin. if ower-up, the adt7460 reads the state of pin 8 is pulled lo w on p ach4/addre pin 9 (t ss select/ therm ) to determine the s. if pin 8 i adt7460s slave addres s high on power-up, the 7460 defaults to sm ribed in more de table 41 to table 81 describe the registers in more detail. table 4. summary inte adt bus slave address 0x2e. this function is desc tail later. internal registers of the adt7460 table 4 summarizes the adt7460s principal internal registers. rnal registers register description configuration these registers provide cont rol and configuration of the adt7460, including alternate pinout functionality. a ddress pointer this register contains the address that selects one of the other internal registers. when writing to the adt7460, the first byte of data is always a register address, which is written to the address pointer register. s tatus registers these registers provide the status of each limit comparison and are used to signal o ut-of-limit conditions on the temperature, voltage, or fan speed channe ls. if pin 14 or pin 5 is configured as smbalert , this pin asserts low whenever an unmasked status bit is set. interrupt mask these registers allow each interrupt status event to be masked when pin 14 or pin 5 is configured as an smbalert output. value and limit the results of analog voltage input, temperature, and fan speed measurements are stored in these registers, along with their limit values. offset these registers allow each temperature channel reading to be offset by a twos comple ment value written to these registers. t min these registers program the starting temperature for each fan under automatic fan speed control. t range these registers program the temperature-to-fan speed cont rol slope in automatic fan speed control mode for each pwm output. operating point these registers define the target operating temperatures for each thermal zone when running under dynamic t min control. this function allows the cool ing solution to adjust dynamically in response to measur ed temperature and system performance. enhance acoustics these registers allow each pwm output contro lling fan to be tweaked to enhance the systems acoustics.
adt7460 rev. c | page 11 of 52 theory of operation serial bus interface c o n t r o l o f the adt7460 is ca r r ied o u t usin g t h e s e r i al s y s t em m a na g e m e n t bus (s mb us). the adt7460 is c o nn ec t e d t o this b u s as a sla v e de vic e , u n der t h e co n t r o l o f a mast er co n t r o l l er . the adt7460 has a 7-b i t s e r i a l b u s addr es s. w h en t h e de vic e is p o w e r e d u p w i t h pin 8 (p wm3 / a ddr e s s e n a b l e ) hig h , t h e adt7460 has a defa u l t s m b u s addr es s o f 0101 110 o r 0x2e. i f m o r e th a n o n e ad t7 46 0 i s t o b e us ed in a s y s t em, ea c h a d t746 0 sh o u l d b e plac e d i n ad dr ess s e l e c t mo de b y st r a p p i n g pin 8 lo w o n p o w e r - u p . th e log i c s t a t e o f p i n 9 t h en de t e r m i n es t h e de vice s s m bus addr es s. th e log i c s t a t e o f t h e s e p i n s is s a m p le d on p o we r - up . the d e v i ce a ddress is s a m p le d and l a tch e d on t h e f i rst va li d s m bus t r a n s a c t io n, m o r e p r e c is e l y , o n t h e lo w- to-hig h tra n si ti o n a t t h e be g i n n i n g o f t h e e i g h th sc l p u lse , w h en t h e s e r i al addr es s b y t e ma t c h e s t h e s e le c t e d sl a v e addr es s. th e s e le c t e d sl a v e addr es s is ch os e n usin g the a ddr e s s e n a b l e / a ddr e s s se l e c t pi ns . a n y a tte m p te d ch ange s i n t h e addr es s has n o ef fe c t a f t e r this. table 5. ad dre ss select mode pin 8 state pin 9 state addres s 0 low (10 k? to g n d) 0101100 (0x2c) 0 high (10 k? pull-up) 0101101 (0x2d) 1 dont care 0101110 (0x2e) (default) adt7460 9 8 addr_sel pwm3/addr_en v cc 10k ? address = 0x2e 03228-014 f i g u re 14. d e fau l t s m bus addr es s 0x 2e adt7460 9 8 addr_sel pwm3/addr_en 10k ? address = 0x2c 03228-015 adt7460 addr_sel pwm3/addr_en address = 0x2d 9 8 v cc 10k ? 03228-016 f i g u re 16. sm bus addr es s 0x 2d (pin 9 = 1) f i g u re 15. sm bus addr es s 0x 2c (p i n 9 = 0) adt7460 9 8 addr_sel pwm3/addr_en nc v cc 10k ? do not leave addr_en a n t a b l e u n c o n n e c t e d . c c a u s e u n p r e d i c addresses care should be taken to ensure that pin 8 (pwm3/addr_en) is either tied high or low. leaving pin 8 floating could cause the adt7460 to power up with an unexpected address. note that if the adt7460 is placed into address selec t mode, pins 8 and 9 can be used as the alternate func - t ions (pwm3, tach4/therm) only if the correct circuit is muxed in at the correct time. 03228-017 f i gure 17. unpredic table smbus a ddr ess if p i n 8 is uncon n ect e d f a c i l i t y to m a ke h a rd w i re d ch ange s to t h e sm bu s sl a v es s al lo ws t h e us er t o a v o i d co nf lic t s w i t h ot h e r de vices t h e e addr sh ar a d t t h e 1. . t h e s e r i a l b u s r e sp o nd to t h e o f i n g t h e s a m e s e r i a l b u s , for e x am pl e, i f more t h an one 7 4 6 0 i s u s ed in a sys t em. s e r i al b u s p r o t o c ol o p era t es as fol l o w s: the mast er ini t ia t e s da ta tra n sfe r b y es ta b l is hing a s t a r t co ndi t i on, def i ne d as a h i g h -to - l o w t r a n si t i o n on t h e s e r i a l da t a l i n e sd a w h i l e t h e s e r i al cl o c k li n e s c l r e ma in s hig h this i ndic a tes t h a t a n ad dr e s s / d a t a st r e a m wi l l fol l o w . al l sl a v e p e r i pher a l s co nn e c te d to st a r co ndi t i o n and sh if t i n t h e nex t eig h t b i ts, con s ist i n g a 7-b i t a ddr ess ( m s b f i rst) pl us a r/ w bi t , w h i c h det e r m i n e t h e dir e c t io n o f t h e da t a t r a n sfer , t h a t is, w h et h e r da t a is wr i t t e n t o o r r e ad f r o m t h e sla v e de vic e . the p e r i ph eral w h os e addr es s c o r r es p o n d s t o t h e t r a n smi t te d ad d r ess r e sp o n ds b y p u l l in g t h e da t a li n e lo w d u ri n g th e l o w pe ri od be f o r e th e n i n t h c l oc k p u l s e , kn o w n a s t h e a c k n ow l e d g e bit . a l l ot h e r d e v i c e s on t h e bu s no r e ma in i d le w h i l e t h e s e le c t e d devi ce w w a i t s f o r da ta t o be re a d f r om or w r i tte n to i t . i f t h e r / w b i t is a 0, t h e mas t er wr i t e s t o t h e sl a v e de vic e . i f t h e r/ w b i t is a 1, t h e mas t er r e ads f r o m th e sla v e de vice .
adt7460 rev. c | page 12 of 52 2 . u r o p sig n a l . the n u m b er ns m o de , t h e mas t er p u l l s t h e da t a li n e be f o r e th e bef o r e the 10th c l o c k p u ls e , t h en hig h d u r i n g t h e 10t h c l o c k p u ls e to ass e r t a sto p co nd i t io n. an y n u m b er o f b y t e s o f da t a ma y b e t r a n sfer r e d o v er t h e s e r i al b u s in on e op er a t io n, b u t i t is no t p o ssi b l e t o m i x r e ad an d wr i t e in on e o p era t ion b e ca us e t h e ty p e o f o p era t ion is det e r m i n e d a t g i s t ers o r r e ad da t a s p o in t e r r e g i s t er . l l u st ra t e d i n f i gur e 18. the d e v i ce a ddress is s e n t o v er th e b u s f o llo w ed b y r/ w d a t a is s e n t o v er th e s e r i al b u s in s e q u en ces of nine c l o c k p u ls es, eig h t b i t s o f da t a fol l o w e d b y an a c k n o w le dg e b i t f r o m th e sl a v e de v i ce . t r a n si tion s o n t h e da ta l i n e m u s t o c c d u ri n g th e l o w pe ri od o f th e c l oc k s i gn al a n d r e m a i n s t a b l e d u ri n g th e h i gh pe ri od , a s a l o w- t o - h igh tr a n si tio n wh en th e clo c k is hig h m a y b e i n t e r p r e t e d as a st o f da t a b y tes t h a t can b e t r a n s m i t te d o v er t h e s e r i a l b u s i n a s i ng l e re a d or w r ite op e r a t i o n i s l i m i te d on ly b y w h a t t h e master an d sl a v e de vices can han d l e . 3 . wh e n a l l d a t a b y te s h a v e b e e n re a d or w r itte n , st op c o nd i t i o a r e es t a b l i s he d . i n wr i t e hig h d u r i n g t h e 10t h clo c k p u ls e t o ass e r t a st o p co ndi t i on. i n r e ad m o de , t h e mas t er de v i ce o v er r i des t h e ack n o w le dg e b i t b y p u lli n g th e da ta lin e hi gh d u ri n g t h e lo w pe r i o d nin t h clo c k p u ls e. this is k n o w n as n o a c k n o w le dge. t h e m a s t e r th e n t a k e s t h e d a ta l i n e lo w d u ri n g th e lo w pe ri o d t h e b e g i n n in g and ca n n ot subs e q uen t ly b e chan ge d wi t h ou t st a r t i n g a ne w op er a t ion. i n t h e cas e o f t h e adt7460, wr i t e o p era t io n s con t a i n ei t h er o n e o r tw o b y t e s, and r e ad op era t ion s co n t ain on e b y t e . t o wr i t e da t a t o o n e o f t h e de vi ce da t a r e f r o m i t , t h e addr es s p o in t e r r e g i s t er m u s t b e s e t s o t h a t t h e co r r e c t da t a r e g i ster is ad dr ess e d . t h e n da t a c a n b e wr i tte n i n t h a t re g i s t e r or re a d f r om it . t h e f i r s t b y te of a w r ite op e r a t i o n al wa ys co n t a i n s a n addr es s t h a t is s t o r e d i n t h e addr es s p o in t e r r e g i s t er . i f da t a i s t o b e wr i t t e n to t h e de vic e , t h e wr i t e o p er a t ion co n t a i n s a s e cond da t a b y te t h a t is wr i t ten to t h e r e g i ster s e le c t e d b y t h e addr es this is i b e i n g s e t t o 0. this is fol l o w e d b y tw o da t a b y t e s. th e f i rs t da t a b y te is t h e addr es s o f t h e in t e r n al da t a re g i ste r to b e w r i t te n to , w h i c h i s store d i n t h e a ddre s s p o i n te r re g i ste r . t h e s e c o nd d a t a b y te i s t h e d a t a to b e w r it te n to t h e in t e r n a l da t a r e g i st er . r/w 0 scl sda 1 1 1 a1 a0 d7 d6 d5 d4 d3 d2 d1 d0 ack. by adt7460 start by master frame 1 serial bus address byte frame 2 address pointer register byte 1 1 ack. by adt7460 9 d7 d6 d5 d4 d3 d2 d1 d0 ack. by adt7460 stop by master frame 3 data byte 1 9 scl (continued) sda (continued) 03228-018 0 9 f i g u re 18. w r it ing a r e g i s t er addres s to t h e addr es s p o in ter r e g i s t e r , th en w r it ing d a t a t o t h e s e lec t ed r e g i s t er
adt7460 rev. c | page 13 of 52 w h en r e adin g da t a f r o m a r e g i s t er , t h er e a r e t w o p o s s i b i l i t ies : ? i f the adt7460 s addr es s p o in t e r r e g i s t er val u e is unk n o w n o r n o t t h e desir e d va l u e , i t is f i rst n e cess a r y t o s e t i t t o t h e co r r e c t va l u e b e fo r e da t a can b e r e ad f r o m t h e d e sir e d da t a r e g i st er . th is is done b y p e r f o r mi ng a wr i t e t o t h e a d t74 60 as b e fo r e , b u t o n ly t h e da t a b y te co n t aini n g t h e r e g i st er addr ess is s e n t b e ca us e d a t a is no t to b e wr i tten to t h e r e g i st er . this is sho w n i n f i gur e 19. a r e ad o p er a t ion is t h en p e r f o r m e d , co n s ist i n g o f t h e s e r i a l b u s addr es s, r/ w b i t s e t t o 1, fol l o w e d b y t h e da t a b y t e re a d f r om t h e d a t a re g i s t e r . t h i s i s sh ow n i n fi g u re 2 0 . ? i f the addr es s p o in t e r r e g i st er is kn o w n t o be al r e ad y a t t h e desir e d a ddr ess, d a t a ca n b e r e a d f r o m t h e co r r esp o nd in g da t a r e g i s t er wi t h o u t f i rst wr i t i n g t o t h e addr es s p o in t e r r e g i s t er , s o f i gu r e 19 ca n be o m i t t e d . it i s p o s s i b l e t o re a d a da t a b y t e f r o m a d a t a r e g i st er w i t h o u t f i rst wr i t in g t o t h e addr es s p o in t e r r e g i s t er if t h e addr es s p o i n t e r r e gis t e r i s al r e a d y a t t h e co rr ec t val u e . h o w e v e r , i t i s n o t pos s i b le to wr i t e d a t a to a re g i ste r w i t h out w r i t i n g to t h e a ddre s s p o i n te r r e g i st er b e ca us e t h e f i rst da t a b y t e o f a wr i t e is a l wa ys wr i t t e n t o t h e addr es s p o i n t e r r e g i s t er . i n f i gur e 18 t o f i gur e 20, t h e s e r i al b u s addr ess is s h o w n as t h e defa u l t val u e 01 011(a1)(a0), wh er e a1 and a0 a r e s e t b y the addr ess s e le c t m o de f u n c t i on p r e v io usly d e f i ne d . i n a d d i t i on to s u pp or t i ng t h e s e nd by te a n d r e c e ive by te p r o t o c ols, th e ad t7460 als o s u p p o r ts the read b y t e p r o t o c ol (see s y s t em m a n a g e m e n t b u s s p eci f i c a t i o n s r e v . 2. 0 f o r m o r e info r m a t io n). i f i t is r e q u ir e d to p e r f o r m s e v e ra l r e ad o r wr i t e o p era t io n s in su c c e s s i on, t h e maste r c a n s e nd a re p e a t st ar t c o nd i t ion inste a d o f a sto p con d i t i o n to b e g i n a ne w o p er a t ion. write operati o ns the s m bus sp e c if ica t ion def i n e s s e v e ra l p r o t o c ols fo r dif f er en t typ e s o f r e ad and wr i t e op era t ion s . th e on es us e d i n t h e adt7460 a r e dis c us s e d b e lo w . the f o l l o w in g ab b r e v ia tio n s a r e us ed in t h e dia g ra m s : ss t a r t p s t o p r r e a d w w r i t e a a c k n o w l e d g e a no a c k n o w l e d g e the adt7460 us es th e f o l l o w in g s m b u s wr i t e p r o t o c ols: se n d b y t e i n t h is o p era t io n, t h e mas t er de vice s e n d s a sing le co mman d b y te to a s l a v e d e v i c e a s fol l o w s : 1. the mast er de vi ce as s e r t s a s t a r t co n d i t ion o n sd a. 2. the mast er s e nds t h e 7-b i t s l a v e addr ess fol l o w e d b y t h e wr i t e b i t (lo w ). 3. the addr es s e d sla v e de vi ce ass e r t s a c k o n sd a. 4. the mast er s e nds t h e r e g i s t er addr es s. 5. the sla v e as s e r t s a c k o n sd a. 6. the mast er ass e r t s a st o p con d i t io n o n sd a and t h e tra n sa cti o n en ds. r/w 0 scl sda 10 1 1 a1 a0 d7 d6 d5 d4 d3 d2 d1 d0 a ck. by adt 74 60 stop by master start by master frame 1 serial bus address byte frame 2 address pointer register byte 1 1 ack. by ad t 7460 9 03228-019 9 f i g u re 19. w r it ing t o t h e addres s p o int e r r e g i s t er o n ly r/ 0 sda 10 1 1 a1 a0 start by master scl d7 d6 d5 d4 d3 d2 d1 d0 no a c k. by ma st er stop by master frame 1 serial bus address a c k a d t7460 byte 1 1 . b y 9 frame 2 d a t a b y t e f r o m a d t 7 4 6 0 03228-020 w 9 ing d a t a f r o m a p r ev i o us ly s e lec t ed r e g i s t er f i g u re 20. r e ad
adt7460 rev. c | page 14 of 52 7 4 60, th e s e n d b y te p r o t o c ol is us ed t o wr i t e t o the f o r th e a d t addr es s p o in t e r r e g i s t er fo r a s u bs e q ue n t sing le -b yte r e ad f r o m th e s a m e addr ess. this is il l u s t ra t e d in f i gur e 21. slave wa s a p register 03228-021 address address 23 15 6 4 g a r e g i st er a ddr ess for subsequ e nt read e l y a f t e r t in a r t d n d c a r r y o u t a si n g le -b yt e r e a d w i t h o u t a s se r t in g a n in t e r m e d ia t e st o p d i h e n d s a co mman d b y t e and 1. e vi ce as s e r t s a s t a r t co n d i t ion o n sd a. s l a v e addr ess fol l o w e d b y t h e wr i t e b i t (lo w ). 3. the ad dr ess e d sla v e de vi ce ass e r t s a c k o n sd a. 4. the mast e s a c k o n sd a. a s s e r t s a c k o n sd a. n f i gur e 22. f i gure 2 1 . s e t t i n i f i t i s r e q u ir ed to r e ad da t a f r o m t h e r e g i st er imm e dia t s e t g u p t h e addr es s, t h e mas t er ca n ass e r t a r e p e a t s t co n i t i on i m m e d i a t ely a f ter t h e f i na l a c k a co n i t i on. wr t e b y t e i n t i s o p era t io n, t h e mas t er de vice s o n e d a t a b y te to t h e sl a v e de v i c e a s fol l o w s : the mast e r d 2. the mast er s e nds t h e 7-b i t r s e nds t h e r e g i s t er addr es s. 5. the sla v e as s e r t 6. the master s e nds a da t a b y te. 7. the sla v e 8. the mast er as s e r t s a s t o p con d i t io n o n sd a t o end t h e tra n sa cti o n . this is i l l u st ra t e d i slave address address f i gure register 24 6 5 3 1 7 8 data a a w sa p 03228-022 22. sing l e -b yte write to a r e gis t er u s r e ad p r o t o c ols. e e re g i s ha ve b e e n s e t u p p r e v i o u sly . i n t h is o p era t ion, t h e mas t er de v i ce re cei v es a si n g le b y t e f r o m a s l a ve a. 2. the mast er s e nds t h e 7-b i t a v e addr ess fol l o w e d b y t h e re a d bit ( vi ce ass e r t s a c k o n sd a. a. a s e n d by t e o r by w r i t e by t e o p e r at i o n . read opera t i o ns the adt7460 us es th e f o l l o w in g s m b re c i v e by te this is us ef u l w h en r e p e a t edl y readin g a sin g le r e g i s t er . t h t e r ad dre s s ne e d s to de vice a s fol l o w s: 1. the mast er de vi ce as s e r t s a s t a r t co n d i t ion o n sd s l h i g h ) . 3. the addr es s e d sla v e d e 4. the mast er r e cei v es a da t a b y t e . 5. the mast er as s e r t s n o a c k on s d 6. the mast er ass e r t s a st o p con d i t io n o n sd a and t h e tra n sa cti o n en ds. i n t h e adt746 0, th e r e cei v e b y t e p r o t o c ol is us ed t o r e ad a s i ng l e b y te of da t a f r om a re g i ste r w h o s e ad dre s s has p r e v iou sly b e e n s e t by slave address sw a a p 03228-023 2 1 3 5 6 4 register address f i g u re 23. sing l e -b y t e r e ad f r om a r e g i s t er alert respons e ad dress r t al lo w m u l the a l e t r e s p o n s e addr es s (ar a ) is a fe a t ur e o f s m bus de v i ces t h a s a n in t e r r u p tin g de vic e t o iden t i f y i t s e lf to th e h o s t w h en t i p le de vice s exis t o n t h e s a m e b u s. sm b a l e r t output c a n b e u s e d a s an i n te r r upt ou tput or ca n b e us e d as an sm b a l e r t . on e o r m o r e o u t p u t s can b e e c te d to a co mm on co n n sm b a l e r t line c o nn e c te d to t e r . i f a de v i ce s t h e m a s sm b a l e r t line g o es lo w , t h e f o l l o w in g 1. oc cu r s : sm b a l e r t is p u l l e d lo w . m a s t e r 2. i n i t i a t e s a r e ad o p era t ion an d s e n d s t h e aler t r e s p o n s e addr ess (ara = 0001 100). this is a gen e ral cal l addr ess, w h ich m u st n o t b e us e d as a sp e c if ic d e v i ce addr ess. 3. the de v i ce w h os e sm b a l e r t output i s l o w re sp ond s to t h e aler t r e s p o n s e addr es s, and t h e mas t er r e ads i t s de vice addr ess. t h e a d dr ess o f t h e d e v i ce is n o w k n o w n, an d i t ca n be in t e r r oga t ed in t h e usual wa y . 4. i f m o r e than one de vice s sm b a l e r t output i s l o w , t h e o n e wi t h t h e lo w e s t de v i ce addr es s has p r io r i ty in acco r d an ce w i t h n o r m a l s m bus a r b i t r a t io n. 5. on ce t h e ad t7 460 has r e s p o nded t o t h e aler t r e s p o n s e addr es s, t h e mas t er m u s t r e ad t h e st a t us r e g i s t e r s a n d t h e sm b a l e r t is cle a r e d o n ly i f t h e er r o r co nd i t io n has gon e aw ay .
adt7460 rev. c | page 15 of 52 smbus timeo u t the adt7460 in c l udes a n s m bus tim e o u t f e a t u r e . i f ther e is n o s m b u s ac ti vi ty f o r 25 m s , th e ad t7460 ass u m e s tha t t h e b u s is lo ck e d an d re le as es t h e b u s. this p r e v en ts t h e de vice f r o m lo c k in g o r h o l d in g t h e s m b u s exp e c t in g da t a . s o m e s m b u s co n t r o l l ers ca nno t ha nd le t h e smbus t i m e o u t fe a t ur e, s o i t can be d i sa b l e d . table 6. co nfig uration register 1 (reg. 0x40) b i t d e s c r i p t i o n <6> t o dis 0: sm bus timeout enabled ( d e fault) <6> t o dis 1: sm bus timeout d i sabled voltage measurement input the adt7460 has o n e exter n a l v o l t a g e m e asu r em en t c h a n ne l . i t ca n also m e asur e i t s o w n s u p p l y v o l t a g e , v cc . p i n 14 ma y be c o nf igur ed t o me as ur e a 2.5 v su p p l y . th e v cc s u p p l y v o l t a g e m e as ur e m en t is ca r r i e d o u t t h r o ug h t h e v cc pi n (p in 3). s e t t in g b i t 7 o f c o nf igu r a t io n reg i st er 1 (reg. 0x40) al lo ws a 5 v s u p p l y t o p o w e r the adt7460 an d be m e as ur ed w i th o u t o v e r r a n g i n g th e v cc m e asur em e n t chan nel. t h e 2 . 5 v in p u t can b e us e d to m o ni to r a chi p s e t su p p ly vol t a g e i n co m p u t er sys t e m s. analog-to-digital converter a l l an a l o g i n put s are m u lt i p l e xe d i n to t h e on - c h i p , su c c e s s i ve a p p r o x im a t io n , a n a l og-to-dig i ta l co n v er t e r . t h is has a r e so l u t i o n o f 10 b i ts. the b a sic in p u t ra n g e is 0 v t o 2.25 v , b u t t h e in p u t has b u i l t-i n a t te n u a t o r s t o a l lo w m e a s ur emen t of 2.5 v w i t h o u t a n y ext e r n al com p on e n ts. t o al lo w t h e t o leran c e o f t h e s u p p l y v o l t a g e , t h e ad c p r o d uces an o u t p u t o f 3/4 f u l l s c ale (768d o r 0x300) f o r th e no minal in p u t v o l t a g e and s o has adeq ua te h e ad r o o m t o d e al wi t h o v er v o l t a g es. input circuitry the i n t e r n al s t r u c t ur e fo r t h e 2. 5 v a n alog in put is sh o w n in f i gur e 24. th e i n p u t c i r c ui t consists o f a n i n p u t p r o t e c t i o n di o d e, a n a t te n u a t or , plu s a c a p a c i tor to for m a f i rst - orde r l o w - p a s s f i l t er t h a t g i v e s t h e i n p u t i m m u ni ty t o hig h f r e q uen c y noi s e . table 7. voltage measureme n t registers r e g i s t e r d e s c r i p t i o n d e f a u l t 0x20 2.5 v reading 0x00 0 x 2 2 v cc reading 0x00 a s s o c i a t e d w i t h t h e v o l t a g e m e as ur em e n t channe ls a r e a hi g h a nd lo w l i mi t r e g i s t er . e x ce e d ing t h e p r og ra mm e d hi g h o r lo w l i m i t ca use s t h e a p p r o p ria t e s t a t us b i t t o be s e t . ex ceed i n g ei t h er limi t can als o g e n e ra t e sm b a l e r t in t e r r u p ts. table 8. 2. 5 v limit registers r e g i s t e r d e s c r i p t i o n d e f a u l t 0x44 2.5 v low limit 0x00 0x45 2.5 v high limit 0xff 0 x 4 8 v cc low limit 0x00 0 x 4 9 v cc high limit 0xff 2.5v in 45k ? 94k ? 30pf 03228-024 f i g u re 24. st ruc t u r e of a n al og input s t a b l e 9 sh o w s t h e in pu t ra n g es o f t h e a n alog in p u ts an d o u t p u t co des o f t h e 10-b i t ad c. w h en t h e ad c is r u nnin g , i t s a m p les a nd con v er ts a vol t a g e in p u t in 711 s a nd a v er a g es 16 co n v ersio n s t o r e d u ce n o is e; a me a s u r e m e n t t a ke s nom i n a l l y 1 1 . 3 8 ms .
adt7460 rev. c | page 16 of 52 table 9. 10-bit a/d output code vs. v in input voltage a/d output 5 v in v cc (3.3 v in ) 1 2.5 v in decimal binary (10 bits) <0.0065 <0.0042 <0.0032 0 00000000 00 0.0065C0.0130 0.0042C0.0085 0.0032C0.0065 1 00000000 01 0.0130C0.0195 0.0085C0.0128 0.0065C0.0097 2 00000000 10 0.0195C0.0260 0.0128C0.0171 0.0097C0.0130 3 00000000 11 0.0260C0.0325 0.0171C0.0214 0.0130C0.0162 4 00000001 00 0.0325C0.0390 0.0214C0.0257 0.0162C0.0195 5 00000001 01 0.0390C0.0455 0.0257C0.0300 0.0195C0.0227 6 00000001 10 0.0455C0.0521 0.0300C0.0343 0.0227C0.0260 7 00000001 11 0.0521C0.0586 0.0343C0.0386 0.0260C0.0292 8 00000010 00 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1.6675C1.6740 1.1000C1.1042 0.8325C0.8357 256 (1/4 scale) 01000000 00 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 3.3300C3.3415 2.2000C2.2042 1.6650C1.6682 512 (1/2 scale) 10000000 00 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 5.0025C5.0090 3.3000C3.3042 2.4975C2.5007 768 (3/4 scale) 11000000 00 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 6.5983C6.6048 4.3527C4.3570 3.2942C3.2974 1013 11111101 01 6.6048C6.6113 4.3570C4.3613 3.2974C3.3007 1014 11111101 10 6.6113C6.6178 4.3613C4.3656 3.3007C3.3039 1015 11111101 11 6.6178C6.6244 4.3656C4.3699 3.3039C3.3072 1016 11111110 00 6.6244C6.6309 4.3699C4.3742 3.3072C3.3104 1017 11111110 01 6.6309C6.6374 4.3742C4.3785 3.3104C3.3137 1018 11111110 10 6.6374C6.4390 4.3785C4.3828 3.3137C3.3169 1019 11111110 11 6.6439C6.6504 4.3828C4.3871 3.3169v3.3202 1020 11111111 00 6.6504C6.6569 4.3871C4.3914 3.3202C3.3234 1021 11111111 01 6.6569C6.6634 4.3914C4.3957 3.3234C3.3267 1022 11111111 10 >6.6634 >4.3957 >3.3267 1023 11111111 11 1 the v cc output codes listed assume that v cc is 3.3 v. if v cc input is reconfigured for 5 v operation (by setting bit 7 of co nfiguration register 1), the v cc output codes are the same as for the 5 v in column.
adt7460 rev. c | page 17 of 52 additiona l adc fu nc tions for voltage measurements a n u m b er o f o t h e r f u n c tio n s a r e a v a i lab l e o n t h e adt7460 t o o f fer th e sys t ems desig n er in cr e a s e d f l exi b ili t y . turn -of f a v eraging f o r e a ch v o l t a g e m e as ur e m en t r e ad f r o m a val u e r e g i s t er , 16 r e a d i n gs h a v e act u all y been m a d e in t e rn all y a n d t h e r e s u l t s a v era g e d b e fo r e b e i n g place d i n t o t h e val u e r e g i s t er . i f t h e us er wa n t s t o sp e e d u p co n v ersio n , s e t t in g bi t 4 o f c o nf igura t ion reg i st er 2 (reg. 0x73) t u r n s a v era g in g o f f . this ef f e c t i v e l y g i v e s a readin g 16 times fas t er (7 11 s ), b u t t h e re a d ing m a y b e n o is ie r . bypass voltag e in put atten u ator s e t t in g b i t 5 o f c o nf igura t ion reg i st er 2 (reg. 0x73) r e m o v e s th e a t t e n u a t i o n ci r c ui tr y f r o m th e 2. 5 v i n p u t . t h i s allo w s th e us er t o dir e c t l y co nn e c t ext e r n a l s e n s o r s o r t o r e s c ale t h e a n alo g v o l t a g e m e asur em e n t i n p u ts fo r o t h e r a p plic a t ion s . th e in pu t ra n g e o f th e ad c wi t h o u t t h e a t t e n u a t o r s is 0 v t o 2.25 v . single-chann el adc con v ersion s e t t in g b i t 6 o f c o nf igura t ion reg i st er 2 (reg. 0x73) p l aces the adt7460 in t o sin g le-c ha nne l ad c co n v ersio n m o de . i n this m o de , t h e adt7460 ca n be made t o r e ad a sing le v o l t a g e c h a nne l o n l y . i f th e in t e r n al adt7460 c l o c k is us ed , t h e s e lec t e d in p u t is r e ad ever y 711 s. th e a p p r o p r i a t e ad c c h a n n e l is s e le c t e d b y wr i t in g t o bi t s <7:5 > o f t h e t a ch1 mini m u m h i g h b y t e r e g i s t er (reg. 0x55). table 10. co nfi g uration register 2 (reg. 0x7 3 ) b i t d e s c r i p t i o n <4> 1: averaging off <5> 1: bypass in put attenuators <6> 1: single-ch a nne l convert mod e table 11. tac h 1 mini mum high byte (reg . 0x55) b i t d e s c r i p t i o n <7:5> selects adc cha nnel for si ngle-c hanne l convert mod e value channe l selecte d 000 2 . 5 v 010 v cc temperature measurement system local t e m p er atu r e me asu r em ent the adt7460 c o n t a i n s a n on-chi p band ga p t e m p era t ur e s e n s o r w h os e ou t p ut is dig i t i ze d b y t h e on-chi p 10-b i t ad c . the 8- b i t m s b tem p er a t ur e da t a is s t o r e d in t h e lo cal t e m p era t ur e r e g i s t er (a ddr e s s 0 x 26). a s b o t h p o si t i v e an d n e g a t i v e t e m p er a t ur es can b e me as ur e d , t h e t e m p era t ur e da t a is s t o r ed in tw os co m p lemen t f o r m a t , as sh o w n in t a b l e 12. the o r e t i cal l y , t h e tem p era t ur e s e n s o r an d ad c ca n me as ur e t e m p era t ur es f r o m ?128c t o + 127c wi t h a r e s o l u tio n o f 0.25c. h o we v e r , t h is exce e d s t h e op era t i n g t e m p era t ur e ra n g e o f t h e de vic e , s o lo cal t e m p er a t u r e m e as ur emen t s o u tside t h is ra n g e a r e n o t p o s s i b le . remote te mp er atu r e me asur em ent the adt7460 c a n m e as ur e t h e t e m p era t ur e o f tw o r e m o t e dio d e s e n s o r s o r dio d e - co n n e c te d t r a n sisto r s c o nn e c te d to p i n s 12 a nd 13, o r p i n s 10 a nd 1 1 . the fo r w a r d vol t a g e o f a dio d e o r dio d e - co n n e c te d t r a n sisto r o p era t e d a t a con s t a n t c u r r en t e x hi b i ts a n e ga t i v e t e m p era t ur e co ef f i cien t o f ab o u t ?2 mv /c. u n fo r t una t e l y , t h e abs o l u te val u e o f v be va r i es f r o m de vice to de vic e , an d i ndivi d u a l ca l i b r a t io n is r e q u ir e d t o n u l l t h is o u t, s o t h e te chniq u e is un s u i t a b le f o r mas s p r o d uc t i o n . th e t e c h niq u e us ed in t h e adt7460 is t o m e as ur e t h e c h an g e in v be wh e n th e d e v i c e i s o p era t e d a t tw o dif f er en t c u r r en ts. this is g i ven b y ( ) n in q kt v be = ? w h er e: k is b o l t z m a n n s co n s t a n t . q is t h e c h a r g e o n t h e ca r r ier . t is t h e a b s o l u te t e m p era t ur e i n k e lvins. n is t h e ra t i o o f t h e tw o c u r r en t s . f i gur e 25 sh o w s th e in p u t sig n a l co n d i t io nin g u s ed t o m e as ur e t h e ou t p u t o f a rem o t e t e m p er a t ur e s e n s o r . this f i gur e s h o w s t h e ext e r n al s e ns o r as a s u b s t r a t e t r a n sis t o r p r o v ide d fo r te m p e r atu r e mon i tor i n g on s o m e m i c r opro c e ss or s . i t c o u l d eq ual l y w e l l be a dis c r e t e tra n sis t o r , s u c h as a 2 n 3904. in i i bias d+ d? lpf v dd v out+ v out? f c = 65khz to adc 03228-025 remote sensing transistor cpu thermda thermdc bias diode f i g u re 25. sig n al condit ion i ng f o r r e mo te d i od e t e m p e r at ure s e ns o r s
adt7460 rev. c | page 18 of 52 i f a di s c r e te t r an sisto r is us e d , t h e col l e c to r is no t g r o u n d e d , and i t sh o u ld b e lin k ed t o t h e bas e . i f a p n p tran sis t o r is us ed , the b a s e i s c o n n e c te d to t h e d ? i n put and t h e e m it t e r to t h e d + i n put . i f a n n p n t r ans i stor i s u s e d , t h e e m i tte r i s c o nne c te d to t h e d? i n p u t, and t h e b a s e t o t h e d+ in p u t. f i gur e 26 a n d f i gur e 27 sh o w h o w t o co nn ec t th e adt7460 to a n npn o r p n p t r a n sist o r fo r t e m p era t ur e m e as ur e m en t. t o p r e v en t g r o u n d n o is e f r o m in t e r f er in g wi t h t h e m e as urem e n t, t h e m o r e ne g a t i ve te r m i n a l of t h e s e n s or i s not re fe re nc e d to g r ou n d but is b i as e d ab o v e g r o u n d b y a n in t e r n al di o d e a t t h e d? in p u t. to m e a s u r e v be , t h e s e ns or i s s w itc h e d b e t w e e n op e r at i n g c u r r en ts o f i a nd n i. the r e su l t in g wa v e f o r m is p a s s e d t h r o ug h a 65 k h z lo w-p a ss f i l t er t o r e m o ve n o is e an d t o a c h o p pe r s t a b ilized a m p l i f i e r th a t pe rf o r m s th e f u n c ti o n s o f a m plif ic a t ion and r e c t if ic a t io n o f t h e w a v e fo r m t o p r o d uc e a dc vo lt age prop or t i on a l to v be . t h is v o l t a g e is me asur e d b y t h e ad c t o g i v e a tem p er a t ur e o u t p u t i n 10-b i t , twos co m p lem e n t fo r m a t . t o f u r t h e r r e d u ce t h e e f fe c t s o f n o is e , d i g i t a l f i lt er in g is p e r f o r m e d b y a v era g in g t h e r e su l t s o f 16 m e as u r em e n t c y cles. a re mote te m p e r a t u r e me a s u r e m e n t t a ke s no m i n a l l y 2 5 . 5 ms . t h e r e s u l t s o f r e m o te t e m p era t ur e m e as ur e m en ts ar e s t o r e d i n 10-b i t, tw os co m p lem e n t f o r m a t , as il l u s t ra t e d in t a b l e 12. the e x tra r e so l u ti o n f o r th e t e m p e r a t ur e m e a s ur em en t s i s h e ld in th e e x t e nded res o l u tio n reg i ster 2 (reg. 0x77) . this g i v e s t e m p era t ur e r e adin gs wi t h a r e s o l u tio n o f 0.25c. 2n3904 npn adt7460 d+ d? 03228-026 f i g u re 26. m e as uri n g t e mpe r at u r e by u s ing an np n t r an s i s t or 2n3906 pnp adt7460 d+ d? 03228-027 table 12. tem p erature data format t e m p e r a t u r e d i g i t a l output (10-bit) 1 ?128c 1000 0000 00 ?125c 1000 0011 00 ?100c 1001 1100 00 ?75c 1011 0101 00 ?50c 1100 1110 00 ?25c 1110 0111 00 ?10c 1111 0110 00 0c 0000 0000 00 +10.25c 0000 1010 01 +25.5c 0001 1001 10 +50.75c 0011 0010 11 +75c 0100 1011 00 +100c 0110 0100 00 +125c 0111 1101 00 +127c 0111 1111 00 1 b o ld d e n o t e s 2 ls bs of m e a s u r e m e n t i n t h e e x t e n d ed re sol u t i on reg i st er 2 (r eg . 0x77) with 0.25c r e solution. table 13. tem p erature meas urement registers r e g i s t e r d e s c r i p t i o n d e f a u l t 0x25 remote 1 temperature 0x80 0x26 local temper ature 0x80 0x27 remote 2 temperature 0x80 0x77 extended resolution 2 0x00 table 14. e x tended resolution tem p erature measurement register bits (addr = 0x 77) b i t m n e m o n i c d e s c r i p t i o n <7:6> tdm2 remote 2 temperature lsbs <5:4> ltmp local temperature lsbs <3:2> tdm1 remote 1 temperature lsbs reading temperature fro m the a d t7460 i t is im p o r t a n t to n o t e t h a t t e m p era t ur e can b e r e ad f r o m t h e adt7460 as a n 8-b i t val u e (wi t h 1c r e s o l u tion) o r as a 10-b i t va l u e ( w i t h 0 . 25 c r e s o l u t i on) . i f o n l y 1 c res o l u t i on i s r e q u ire d , t h e t e m p era t ur e r e adin gs can b e r e ad b a ck a t an y t i m e and i n no pa r t i c ul a r o r d e r . f i g u re 27. m e as uri n g t e mpe r at u r e by u s ing a pn p t r a n s i s t or i f t h e 10- b i t me asur em e n t is r e q u ir e d , t h is i n volv es a 2-r e g i st e r r e ad fo r e a ch me as ur emen t. the ext e n d e d r e s o l u t i o n r e g i st er (reg. 0x77) s h ou ld be r e ad f i rs t. this c a us es al l t e m p era t ur e r e ading r e g i s t ers t o b e f r oze n u n t i l al l tem p era t ur e r e ading r e g i s t ers ha ve b e en r e ad f r o m . this p r ev en ts an ms b r e adin g f r o m b e in g u p da t e d w h i l e i t s two ls bs a r e b e ing r e ad , an d vice ve rs a.
adt7460 rev. c | page 19 of 52 nulling out temperat ure e rrors a s cpu s r u n fas t er , i t becom e s m o r e dif f i c u l t to a v o i d hig h f r e q uen c y clo c ks w h en r o u t in g t h e d+, d? t r ac es a r o u n d a sys t em b o a r d . e v en w h e n r e commende d l a yo u t guide l i n es a r e fol l o w e d , t h er e ma y s t i l l b e t e m p era t ur e er r o rs a t t r i b u t e d t o noi s e b e i n g c o upl e d on to t h e d + / d ? l i ne s . h i g h f r e q u e nc y n o is e g e n e ral l y has t h e ef fe c t o f g i vi n g t e m p er a t ur e m e as ur e - m e n t s tha t a r e to o hig h b y a con s tan t am o u n t . the adt7460 has t e m p era t ur e o f fs et r e g i s t ers a t a d dr es s e s 0x 70, 0x72 f o r th e re m o te 1 an d r e m o t e 2 t e m p er a t ur e chan n e ls. by do in g a on e- t i m e c a lib r a t ion o f t h e sys t e m , on e ca n det e r m i n e t h e o f fs et ca us e d b y sys t e m b o a r d n o is e and n u l l i t o u t usin g t h e o f fs et r e g i s t ers. th e o f fs et r e g i s t ers a u to ma t i c a l l y add a tw os co m p le m e n t 8- b i t r e adi n g t o e v er y t e m p era t ur e m e as ur emen t. the ls b adds 0. 25c o f fs et t o t h e tem p era t ur e r e ading s o t h e 8-b i t r e g i s t er ef fe c t i v e l y al lo ws tem p er a t ur e o f fs ets o f u p t o 32c wi t h a r e s o l u tio n o f 0.25 c. this en s u r e s tha t t h e r e adin gs in t h e tem p er a t ur e m e as ur em e n t r e g i st ers a r e as acc u ra t e as p o ssi b le. table 15. tem p erature offset registers r e g i s t e r d e s c r i p t i o n d e f a u l t 0x70 remote 1 tempera ture offset 0x00 (0c) 0x71 local temper ature offset 0x00 (0c) 0x72 remote 2 tempera ture offset 0x00 (0c) tem p er at ur e meas ur em ent limit register s a s s o c i a t e d w i t h e a ch t e m p era t u r e m e as ur emen t cha nne l a r e h i gh a n d l o w lim i t r e gi s t e r s . ex c eed in g th e p r ogra m m ed h i gh o r lo w limi t ca us es t h e a p p r o p r i a t e st a t us b i t t o b e s e t. e x ce e d in g ei t h er limi t ca n als o g e n e ra t e sm b a l e r t in t e r r u p ts. table 16. tem p erature meas urement limit registers r e g i s t e r d e s c r i p t i o n d e f a u l t 0x4e remote 1 temperature low limi t 0x81 0x4f remote 1 temperature high lim i t 0x7f 0x50 local temper ature low limit 0x81 0x51 local temper ature high limit 0x7f 0x52 remote 2 temperature low limi t 0x81 0x53 remote 2 temperature high lim i t 0x7f overt e mp er at ur e events o v er t e m p era t u r e e v en ts o n an y o f t h e t e m p era t ur e cha nne ls can b e dete c t e d and de a l t w i t h a u toma t i c a l l y in a u to ma t i c fan sp e e d co n t r o l m o de . reg i s t ers 0x6a t o 0x6c a r e th e therm limi ts. w h en a t e m p er a t ur e exce e d s i t s therm limi t, al l fan s r u n a t 100% d u ty c y c l e . the fa n s con t in ue r u nning a t 100% un t i l t h e t e m p era t ur e dro p s b e lo w therm C h y s t er esis. (this c a n b e dis a b l e d b y s e t t i n g t h e b o o s t b i t in c o nf igura t io n reg i ster 3, bi t 2, r e g i s t er 0 x 78). th e h y s t eresis val u e fo r t h a t therm limi t is th e val u e p r o g ra mm e d in t o reg i st ers 0x6d a nd 0x6e (h ys t e r e sis r e g i st ers). th e de fa u l t h y s t er esis val u e is 4c. fans temperature 100% hysteresis = ( c) therm limit 03228-028 f i g u re 28. therm limit o p er at ion additi on a l adc fu nc tio n s for temperature measurement a n u m b er o f o t h e r f u n c tio n s a r e a v a i lab l e o n t h e adt7460 t o o f fer t h e sys t ems desig n er i n cr e a s e d f l exi b i l i t y : ion g . 0x73) t u r n s a v era g in g o f f . this tak e s a r e adin g e n t t a k e s s 1.4 m s . e - c h v ersions g b i t e g . 0x73) p l aces the d t 7 4 6 0 i n t o sin g le-c ha nne l ad c co n v ersio n m o de . i n this o de , t h e adt7460 ca n be made t o r e ad a sing le t e m p era t ur e y wr i t i n g i t s < ch1 m i nim u m h i g h b y t e r e g i st er x 1 7 i g u r a t i o n r e g i s t e r 2 ( turn -of f a v eraging f o r ea c h t e m p era t ur e m e as ur e m en t r e ad f r o m a v a l u e r e gis t e r , 16 r e a d i n gs ha ve a c t u all y be en m a d e in t e rn all y a n d t h e r e s u l t s a v era g e d b e fo r e b e i n g place d i n t o t h e val u e r e g i s t er . s o m e t i m e s i t ma y be n e ces s a r y t o tak e a v e r y fas t meas ur em en t, f o r exa m ple , o f cp u t e m p era t ur e . s e t t in g bi t 4 o f c o nf igura t reg i st e r 2 ( r e e v er y 15.5 m s . e a ch r e m o t e te m p era t ur e m e asur em 4 m s a nd t h e lo cal t e m p er a t ur e m e as ur e m en t t a k e s i n g l a n n el adc con s e t t i n 6 o f c o nf igura t ion reg i st e r 2 ( r a m chan nel on ly . t h e a p p r op r i a t e ad c chan nel i s s e le c t e d b t o b 7 : 5 > o f t h e t a ( r e g . 0 5 5 ) . table . c o n f r e g . 0x7 3 ) bit description <4> 1: averaging off <6> 1: single-ch a nne l convert mod e t a b l e 18. tac h 1 mini mum high byte (reg . 0x55) i t d e s c r i p t i o n b <7:5> selects adc cha nnel for si ngle-c hanne l convert mod e value channe l selecte d 101 remote 1 temp 110 local temp 111 remote 2 temp
adt7460 rev. c | page 20 of 52 a n d i n t e r r u p t s u es a t ed wi th e a t c h a n ne l o n t h e adt7460 h and lo w l i r m t h e b a sis o f m o ni t o r i n g : e s e t fo r a n y o u t i t i on an d d e te t h e d e vice. a l ter n , b a l e r t l i m i t s , s t a t u s r e g i s t e r s , l i m i t v a l a s s o c i c h m e asur emen a r e h i g m i ts. th es e ca n f o sys t e m st a t u s a s t a t us b i t c a n b - o f - l i m co ndi t c t e d b y p o l l i n g a t i v e l y sm i n te r r upt s c a n b e ge ne r a te d to f l ag a pro c e s s o r or . i t s l l o w in g is 6 t a b l e 1 9 . v o l t a i t registers e r l t m i c r o c on t r o l l e r of out - of - l i m it c o n d i t i o n s 8 - b i t l i m the f o a lis t o f 8-b i t l i mi ts on t h e a d t 7 4 0 . g e l i m r e g i s t d e s c r i p t i o n d e f a u 0x44 2.5 v low limit 0x00 0x45 2.5 v high limit 0xff 0x48 v cc low limit 0x00 0x49 v cc high limit 0xff table 20. tem p e limit registers e r l t e r a t u r r e g i s t d e s c r i p t i o n d e f a u 0x4e remote 1 temperature low limi t 0x81 0x4f r e m o t e 1 t e m p e r a t u r e h i g h 0x7f limit 0x6a remote 1 ther m l i m i t 0 x 6 4 0x50 local temper ature low limit 0x81 0x51 local temper ature high limit 0x7f 0x6b local ther m limit 0x64 0x52 remote 2 temperature low limi t 0x81 0x53 remote 2 temperature high limit 0x7f 0x6c remote 2 ther m limit 0x64 table 21. therm tim e r limit register r e g i s t e r d e s c r i p t i o n default 0x7a ther m t i m e r l i m i t 0 x 0 0 1 6 - b i t l i m i t s t a ch u l t s. the fa ch r e als o 1 y te a nd lo . a ns r u n r e no r m a n ly i on s o f in r fa n t a n t a ch a s ur ed , e x g the fan m e as ur e m en ts ar e 16-b i t r e s n t a limi ts a s i n c e f 6 b i ts, co n s is ting o f a hig h b n i n g u n der sp e e d o r st a l le d a w b y t e l ly t h e o co ndi t ter e st, o n ly hi g h limi ts ex ist fo ch s. s i n c e fa pe ri od i s a c t u all y be i n g m e fa n. ceed in th e li mi t in d i c a t e s a s l o w o r s t alled table 22. fan l i mit registers register description d e f a u l t 0x54 tach1 minimum low byte 0xff 0x55 tach1 minimum high byte 0xff 0x56 tach2 minimum low byte 0xff 0x57 t a c h 2 m i n i m u m h i g h b y t e 0xff 0x58 tach3 minimum low byte 0xff 0x59 t a c h 3 m i n i m u m h i g h b y t e 0xff 0x5a tach4 minimum low byte 0xff 0x5b tach4 minimum high byte 0xff out - of-limit c o mparisons on ce al l limi ts ha v e been p r og ra mmed , t h e adt7460 can be ena b led f o r m o ni t o r i ng. the ad t7460 m e as ur es al l p a ra m e ters in r o u n d - r o b i n fo r m a t a nd s e t s t h e a p p r o p r i a t e st a t us b i t fo r o u t-o f -li m i t co ndi t i on s. c o m p ar is o n s a r e do ne dif f er en t l y dep e ndin g o n w h et h e r t h e m e asur e d val u e is b e in g co m p a r e d to a hig h o r lo w limi t. ? h i g h l i m i t : > c o m p ar i s on p e r f or me d ? l o w l i m i t : < or = c o m p ar i s on p e r f or me d 03228-029 no int l o w l i m i t temp > low limit f i g u re 29. t e mpe r a t ur e > l o w l i mit : n o int int low limit temp = low limit 03228-030 f i g u re 30. t e mpe r a t ur e = l o w l i mit : int oc c u r s
adt7460 rev. c | page 21 of 52 no i n t t e m p = h i g h l i m i t h i g h l i m i t 03228-031 f i gure 3 1 . t e m p er atur e = hi gh l i mi t: no int int high limit temp > high limit 03228-032 f i gure 3 2 . t e m p er atur e > hi gh l i mi t: int oc c u r s analog monit o ring cycle ti me the a n alog m o ni t o r i ng c y cle b e g i n s w h en a 1 i s wr i t t e n t o t h e s t a r t b i t (b i t 0) o f c o nf igura t ion reg i s t er 1 ( r eg. 0x40). th e a d c m e a s ur es ea c h a n alog in p u t i n t u rn a n d , as ea c h m e n t is com p lete d , t h e r e su l t is a u t o m a t i c a l l y sto r e d in t h e a p p r o p r i a t e v a l u e r e g i s t er . this r o un d-r o b i n mo ni t o r i n g c y cle con t in ues u n l e ss dis a b l e d b y wr i t ing a 0 t o bi t 0 of c o nf igu r a t io reg i st er 1. a s t h e ad c is n o r m a l ly a l lo w e d t o f r e e -r un in t h is ma n n er , t h e t i m e t a ken to mo ni to r a l l t h e a n a l o g in p u ts is no r m a l ly n o t o f in t e r e st, sin c e t h e m o s t r e ce n t ly m e as ur e d val u e o f a n y in p u t c a n b e r e a d o u t at a n y t i m e . fo r ap p l i c at i o n s w h e r e t h e m o ni t o r i n g c y c l e tim e is im p o r t a n t, i t can easil y be c a lc u l a t e d . m e as ur e- n the t o t a l n u m b er o f cha nne ls m e as ur e d is ? t w o sup p ly vol t age i n p u t s ( 2 . 5 v and v cc ) ? l o c a l t e m p era t ur e ? t w o re mote te m p e r a t u r e s a s m e n t ion e d pr e v io usly , t h e a d c p e r f o r m s r o und-r o b i n co n v ersio n s and tak e a g e m e as ur emen t, d 2 5 . 5 m s f o r eac h o t e re a e t o t to r i n g c y p e r m o ni t o r i n (2 11.38) + 12 ( 2 e r o und r o b i n st a r ts s e as p p r o x i m f a n t a ch m e a s ur em e syn c h r o n i z e d wi th t h e a ur em en t s in a n y w a y . a t u g i s t e r e s u l t s o f limi t com us reg i st ers 1 t u s r e g i s t er b us h e l a a s u r e m e n l . i f a m e asur e m e n t is wi t h g st a t us g i st er b i t is cle a r e d t o 0. i f t h e m e a s ur e m en t is o u t-o f -li m i t s, th e co r r es p o ndin g s t a t us r e g i s t er b i t is s e t t o 1. the s t a t e o f t h e va r i o e ls ma y b e p o l l e d b y r e adin g t h e sta t us r e g i st ers o e s e r i al b u s. i n b i t 7 m e a n s tha t an o u t-o f - t ev f l a r e gi s t e r 2. t h i s m e a n s t yo y r e a d s e t. al ter n a t i v e l y , p i n 5 o r p ed as a n b a l s 11.38 m s fo r e a c h v o l t 12 m s f o r a lo ca l t e m p era t ur e r e adin g , a n re m t e m p e r a t u r e d i n g . t h a l m o ni cle t i m e fo r a v era g e d v o l t a g e and t e m a t ur e g i s , t h erefo r e , n o minal l y 2 5 . 5 ) = 8 5 . 76 m s t h a g a i n 3 5 m s la ter . t h erefo r e, a l l cha n n e l a t e l y ever y 120 m s . a r e m ur ed a n ts a r e made i n p a r a l l el a nd a r e n o t n alog m e a s s t s r e s r e s t o r e d in s t a t the r p a r is o n s a a nd 2. th of t e s t a st me i t fo r e a ch cha n ne l r e f l e c ts t h e st a t t a n d l i m i t c o m p ar i s on on t h a t ch an ne i n li mi ts, t h e co r r esp o ndin r e u s m e as ur em e n t chann v er th (o o l ) o f s t a t us reg i st er 1 (reg . 0 x 4 1 ) , 1 l i m i en t h a s been g g e d in s t a t us t h a u need onl s t a t us reg i st er 2 w h en this b i t i s i n 14 can b e co nf igur s m e r t o u t p u t . t h sup e r v i s or of an out - of - e a d i n g t h e st atu s i s t e r rs t h e a p p r co ndi tion tha t c a us ed t h b i ts a r e s t i ck y . w h e n e t- o f -limi t con d i t i o n, i t r e e d i t g o n ( u nt i l r e i t is t o r e ad t h e st a t us r e g i n t e r - t s t a s k r e g i s t e i n te r r upt s o u r c e s to b e b a l e r t is a u t o m a ticall y n o t i f i e s th e sys t em l i m it c o n d i t i o n . r r e g s c l e a o p r i a t e st a t us b i t as lon g as t h e er r o r e in t e r r u p t has c l ea r e d . s t a t us r e g i st e r v er a st a t us b i t is s e t, i ndi ca t i n g a n o u m a i n s s e t e v e n if t h e e v en t t h a t c a us h a s e aw ay a d ) . t h e o n l y w a y t o c l e a r t h e s t a t u s b s t er a f t e r t h e e v e n t h a s g o n e a w a y . i r u p t u s m a r s ( r eg. 0x74, 0x75) al l o w individ u al m a ske d f r om c a u s i n g a n sm . we ve e of t h e s e of - limi t, i t s a s s o cia t ed st a t u s t a t us r e gis t e r s. h o r , i f o n m a ske d i n te r r upt s o u r c e s go e s out - s b i t is set in t h e in t e rr u p t ool = 1 denotes a parameter monitored through status reg 2 is out-of-limit 03228-033 f i g u re 33. st at us r e g i s t e r 1
adt7460 rev. c | page 22 of 52 a b l e 23. status register 1 (re g . 0x41) n t bit mnemonic d e s c r i p t i o 7 ool 1 denotes a bit in status registe r 2 is set and status register 2 should be r e a d . 6 r2t 1 indicates that the remote 2 temperature high or low limit ha s b e e n exceeded. 5 lt 1 indicates that the local temperature high or low limit has been e x cee d ed. 4 r1t 1 indicates that the remote 1 temperature high or low limit ha s been exceeded. 3 - unused 2 vcc 1 indicates that the vcc high or low limit has bee n e x ceeded. 1 - unused 0 2.5 v 1 indicates that the 2.5 v high or low limit has bee n e x ceeded. 03228-034 f4p = 1, fan 4 or therm timer is out-of-limit f i g u re 34. st at us r e g i s t e r 2 table 2 4 . s t a t u s r e g i s t e r 2 ( r e g . 0x42) bit mnemonic description 7 d2 1 indicates an o p en or sh ort on d 2 + / d 2 ? i n p u t s . 6 d1 1 indicates an o d2+/d2? inputs. p en or sh ort on 5 f4p 1 indicates t h a t f a n 4 h below minimu m s p e e d . a s dropped a l t e r n atively, indicates that ther m timer limit has been exc eeded if the ther m timer function is used. 4 fan3 1 indicates t h a t f a n 3 h a s dropped below minimu m speed. 3 fan2 1 i n d i c a t e s that fan 2 has dropped below minimu m speed. 2 fan1 1 indicates that fan 1 has dropped below minimu m speed. 1 ovt 1 indicates that a ther m overtemperatur e limit has bee n exceeded. 0 - unused s m b a l e r t interrupt b e h a vior the adt7460 c a n b e p o l l ed f o r s t a t us, o r a n sm b a l e r t in ter r u p t ca n b e gen e r a te d fo r o u t-o f -li m i t co nd i t io n s . i t is i m p o r t a n t to note h o w t h e sm b a l e r t o u t p u t a nd st a t us b i t s b e ha ve w h e n w r i t in g in ter r u p t ha nd ler s o f t w a r e . fi g u r e 3 5 s h ow s h o w t h e sm b a l e r t ou t p ut and st ic ky st a t u b i ts b e ha v e . o n ce a li mi t is exce e d e d , t h e co r r es p o n d in g s t s a t us r o r co ndi t i o n ides u s . the s t a t us b i ts a r e r e fer r e d s st i nc e t h e y e n su re s t h at an out - of - i f s o f t w a re o l l in vice p e r t b i t is s e t t o 1. th e st a t us b i t r e ma in s s e t u n t i l t h e er s u b s and t h e s t a t r e g i st er is r e a d to a c ky s i r e m a i n s e t u n t i l re a d b y s o f t w a re. t h i s l i m it e v e n t c a n n ot b e m i ss e d is p g t h e de r i o d ic a l ly . n o t e t h a t t h e sm b a l e o u t p u t r e m a i n s lo w f o t i o n tha t a r e a d i n g i s o u t- n t i l t h e s pli c a n h o w s r t h e en ti r e d u ra o f -limi t an d u t a t us r e g i st er has b e en r e ad . t h is has im t io n s o o f t wa r e h a n d les t h e i n t e r r u p t . ? sticky ? status bi t h i g h l i m p e r i t t e m a t u r e cleared on read l o w l i m i t ) temp back in limit ( s ( t e m p b e t a t u s b i t s t a y s s e t ) smbalert 03228-035 b a lert f i g u re 35. s m and stat us bit be havior h a n d m b a l l i n g s e r t interrupts t o p r e v e y s t em f t e r r u p ts, i t e co m t o ha n d l n t t h e s r o m b e i n g t i e d u p s e r v i c in g i n i s r m e n d e t h e sm b a l e r t in t e r r u p t as fol l o w s: e r t 1. de t e ct th e sm b a l ass e r t io n. . e n te r t h e i n te r r upt h a nd l e r . r r u p t s o ur ce . t i on fo r a g i v e n in t e r r u p t s o ur ce . p e r i o d i c al l y g i st ers. i f t h e i n ter r u p t s t a t us b i t has cl e a r e d , r e s e t t h e co r r esp o ndi n g i n t e r r u p t mask b i t 2 3. re ad t h e st a t us r e g i s t ers t o ide n t i f y t h e in t e 4. m a s k t h e i n t e r r u p t s o ur ce b y s e t t in g t h e a p p r o p r i a t e mask b i t in t h e in t e r r u p t mask r e g i s t ers (reg. 0x74, 0x75). 5. t a k e t h e a p p r o p r i a t e ac 6. ex i t th e in t e e r . rr u p t h a n d l 7. p o l l t h e s t a t us r e t o 0. this c a us es th e sm b a l e r t o u t p u t and st a t us b i ts to ve as sh r e 36. b e h a o w n in f i g u
adt7460 rev. c | page 23 of 52 ?sticky? status bit (temp below limit) temp back in limit (status bit stays set) interrupt mask bit set cleared on read high limit temperature smbalert 03228-036 interrupt mask bit cleared (smbalert rearmed) f i gure 3 6 . ho w m a sk i n g the interrupt so ur c e a ffects smb a lert ou t p u t m a sk i n g i n te rr u p t s o ur ce s i n ter r u p t m a sk reg i st ers 1 an d 2 a r e lo ca t e d a t a ddr ess e s 0x74 a nd 0x7 5 . th es e al lo w i n divi d u a l i n t e r r up t s o ur c e s t o b e mas k e d o u t t o p r e v en t sm b a l e r t i n te r r upt s . n o te t h a t ma sk i n g an in t e r r u p t s o ur ce p r e v en ts only t h e sm b a l e r t output f r o m b e i n g a s s e r t e d ; t h e ap p r o p r i at e s t at u s b i t i s s e t a s n o r m a l . table 25. i n ter r upt mask r e gister 1 (reg. 0 x 7 4 ) bit mnemonic description 7 ool 1 masks smbaler t for any alert condition flagged in statu s register 2. 6 r2t 1 masks smbaler t for remote 2 temperature. 5 lt 1 masks smbaler t for local temperature. 4 r1t 1 masks smbaler t for remote 1 temperature. 3 - unused 2 vcc 1 masks smbaler t for the vcc channel. 1 - unused 0 2.5 v 1 masks smbaler t for the 2.5 v channel. table 26. i n ter r upt mask r e gister 2 (reg. 0 x 7 5 ) bit mnemonic description 7 d2 1 masks smbaler t f o r d i o d e 2 e r r o r s . 6 d1 1 masks smbaler t f o r d i o d e 1 e r r o r s . 5 f a n 4 1 masks smbaler t for fan 4 failure. if the tach4 pin i s being used as t h e ther m i n p u t , t h i s b i t m a s k s s m b a l e r t for a ther m event. 4 fan3 1 masks smbaler t for fan 3. 3 fan2 1 masks smbaler t for fan 2. 2 fan1 1 masks smbaler t for fan 1. 1 ovt 1 masks smbaler t for overtemperature (exceeding ther m limi ts). 0 - unused enabling the smbalert interrupt output the sm b a l e r t in t e r r u p t f u n c tion is dis a bled b y defa u l t. p i n 5 o r p i n 1 4 c a n b e r e conf igure d as a n sm b a l e r t o u t p u t t o s i g n al out - of - l i m it c o n d i t i o n s . table 27. co nfi g register 4 (r eg. 0x7 d ) pin no. bit setting 14 <0> al2.5v = 1 table 28. co nfi g register 3 (r eg. 0x78) pin no. bit setting 5 <0> alert = 1 to assign therm fun c tionality to p i n 9 pin 9 can b e conf igur e d as t h e therm p i n o n t h e ad t7460. t o conf igure pi n 9 a s t h e therm pi n , s e t t h e therm en ab l e b i t (b i t 1) in c o nf igura t io n reg er 3 (a ddr ess 0x78) = 1. therm i s t as a n i n p u t w h en co nf igur e d as a n in p u t, t h e therm p i n al lo ws t h e u s er ef u l f o r co nn ec tin g t o tim e ass e r t io n s o n t h e p i n. this ca n be us to t h e pr o c h o t output of a c p u to g a u g e s y st e m p e r f or m a nc e. r f o m o r e info r m a t io n on t i mi n g therm ass e r t i o n s and ge ne r a t i ng sm b a l e r t s bas e d o n therm , s e e t h e g e ne r a t i ng r u p ts f r o m e v en ts s e c t io n. i n ter m the us er can als o s e t u p t h e adt7460 s o w h en th e t h e r pi n i the fa n s r u n a t is dr v en lo w ex t e r n al l y , t h e fa ns r u n a t 100%. 100% while t h e therm pi n i s pu l l e d l o w . t i s ion reg i this w o rks o n l y if the fa n is e a e w h en t h e r r t e min min th e d ty c y c l e in ma n u al m o de is s e t t o 0x00, p u l l in g therm h i s d o n e b y s e t t in g t h e b o os t b i t (bi t 2) i n c o nf igura t st er 3 (a ddr es s 0x78) t o 1. a l r d y r u nning , fo r ex a m ple, in ma n u a l m o d c u en t d u ty c y cle is a b o v e 0x00 o r in a u t o ma t i c m o de w h e n t h e m p era t ur e is ab o v e t . i f t h e t e m p era t ur e is b e lo w t or i f u . lo w ex t e r n al l y has n o ef fe c t . s e e f i gure 3 7 fo r mo r e info r m a t i o n therm t min therm asserted to low as an input. fans do not go to 100% since temperature is below t min . therm asserted to low as an input. fans go to 100% since temperature is above t min and fans are already running. 03228- 037 f i gure 3 7 . a sser t i n g therm l o w as an input i n automat i c f a n spe e d c o ntr o l m o de
adt7460 rev. c | page 24 of 52 therm timer the adt7460 has a n in t e r n al t i mer t o meas ure therm a s se r t i o n tim e . f o r e x a m p l e , th e therm in pu t m a y b e co nn e c te d to t h e pro c h o t output of a p e n t iu m 4 c p u a n d e as ur e sys t em p e r f o r ma n c e . th e therm m in p u t m a y a l s o b e c o nne c te d to t h e out p ut of a t r ip p o i n t te m p e r a t u r e s e ns or . the tim e r is star t e d o n t h e ass e r t io n o f th e adt7460 s therm i n put a n d stopp e d on t h e n e g a t i on of t h e pi n . t h e t i me r c o u n t s therm t i m e s c u m u la t i v e l y , t h er efo r e , t h e t i m e r r e s u mes c o u n t i ng on t h e ne x t therm ass e r t io n. the therm ti m e r c o n t i n u e s to a c c u m u l a te therm a s se r t io n tim e s un til t h e t i me r i s re a d ( i t i s cl e a re d on re a d ) or u n t i l it re a c he s f u l l s c a l e. i f th e co un t e r r e a c h e s full scale , i t s t o p s a t tha t r e a d in g un til cl e a re d. the 8- b i t therm tim e r r e gi s t e r (r eg . 0x7 9 ) i s d e s i gn ed s u c h t h a t bi t 0 is s e t to 1 o n t h e f i rst therm ass e r t io n. o n ce t h e cu m u la ti v e therm as s e r t io n tim e exce eds 45.52 m s , b i t 1 o f th e therm t i me r i s s e t an d bi t 0 b e c o me s t h e l s b of t h e t i me r wi th a r e s o l u tion o f 22.76 m s . f i gur e 38 il l u s t ra t e s h o w t h e therm ti m e r be ha v e s a s th e therm in p u t is ass e r t e d an d nega t e d . bi t 0 is s e t on t h e f i rst therm ass e r t io n d e t e c t e d . t h is b i t r e m a in s s e t un t i l t h e cu m u la ti v e therm as s e r t io n s exceed 45.52 m s . a t this tim e , bi t 1 of t h e therm ti m e r i s se t , a n d b i t 0 i s c l ea r e d . b i t 0 n o w re f l e c t s t i me r re a d i n g s w i t h a re s o lut i o n of 2 2 . 7 6 ms . therm therm timer (reg. 0x79) therm asserted 22.76ms 76 5 3210 4 00 0 0001 0 therm timer (reg. 0x79) therm asserted 45.52ms 76 5 3210 4 00 0 0010 0 therm timer (reg. 0x79) therm asserted 113.8ms (91.04ms + 22.76ms) 76 5 3210 4 00 0 0101 0 therm accumulate therm low assertion times therm accumulate therm low assertion times 03228-038 f i gure 38. u n ders t a ndi n g the therm whe n u s i n g t h e therm ti m e r , be a w a r e o f th e f o llo w i n g: af t e r a therm tim e r r e ad (reg. 0x79) the co n t en ts o f t h e t i m e r is cle a r e d o n r e ad. ? the f4p b i t (b i t 5) o f s t a t us reg i s t er 2 n e e d s t o be c l ea r e d ( a ssu mi ng t h e therm ? l i m i t h a s bee n ex ceed ed ). if t h e therm t i m e r is re ad d u r i n g a therm ass e r t io n ? the co n t en ts o f t h e t i m e r a r e cle a r e d . ? bi t 0 of t h e therm timer is s e t t o 1 (sin ce a therm ass e r t io n is o c c u r r in g). ? the therm ti m e r in cr em en t s f r o m 0. ? if t h e therm limi t ( r eg. 0x7a) = 0x00, th e f4p b i t is s e t. generating smbalert in terrupts from therm events the adt746 0 c a n g e ner a t e sm b a l e r t s w h en a p r og r a mmab l e therm l i m i t h a s bee n e x ceed ed . t h i s all o w s t h e s y s t em s desig n er t o ig n o r e b r ief, inf r e q u e n t therm ass e r t io n s w h i l e ca p t ur in g lon g er therm e v en ts. r e g i s t er 0x7a is t h e therm limi t r e g i s t er . this 8-b i t r e g i s t e r al lo ws a limi t f r o m 0 s e co nds (f ir s t therm as s e r t io n) t o 5.825 s e co n d s t o be s e t bef o r e a n sm b a l e r t i s ge ne r a te d. t h e therm tim e r v a l u e is co m p a r ed wi t h t h e co n t en ts o f t h e therm limi t reg i s t er . i f t h e therm t i m e r val u e exc e e d s t h e therm limi t val u e , t h e f4p b i t (b i t 5) d an sm b a l e r t o f s t a t us reg i s t er 2 is s e t an ti m e r i s ge ne r a te d. n o te tha t t h e f4p b i t (b i t 5) o f m a s k reg i st er 2 (reg. 0x75) mas k s o u t sm b a l e r t s if t h is b i t is s e t t o 1, a l t h o u g h t h e f4p b i t o f i n ter r u p t s t a t us reg i st er 2 is st i l l s e t if t h e therm limi t is e x ceed ed . f i gur e 39 is a f u n c t i o n a l b l o c k d i a g ra m o f t h e therm ti m e r , limi t, an d as s o c i a t ed c i r c ui tr y . w r i t in g 0x00 t o th e therm limi t r e g i s t er ( r eg. 0x7a) c a us e s sm b a l e r t to b e ge ne r a te d on t h e f i r s t therm ass e r t io n. a therm limi t of 0x01 ge ne r a te s an sm b a l e r t o n ce c u m u la t i ve therm ass e r t io n s exceed 45.52 ms.
adt7460 rev. c | page 25 of 52 22.76ms 45.52ms 91.04ms 182.08ms 364.16ms 728.32ms 1.457s 2.914s in out e s e t a t c h r l cleared on read f4p bit (bit 5) mask register 2 1 = mask (reg. 0x75) f4p bit (bit 5) status register 2 comparator 22.76ms 45.52ms 91.04ms 182.08ms 364.16ms 728.32ms 1.457s 2.914s 7 6 5 4 3 2 1 0 7 6 5 4 3 2 10 therm limit (reg. 0x7a) therm timer (reg. 0x79) therm timer cleared on read smbalert therm 03228-039 r a m of a d t 7 4 60 therm f i g u re 39. f u nc t i o n al d i ag s mon i to ring circuitr y
adt7460 rev. c | page 26 of 52 configuring t h e desired therm b e h a v i o r 1. c o nfigure the therm i nput . se t t i n g b i t 1 ( therm en able) o f c o n f igura t io n reg i st er 3 (reg. 0x78) ena b les th e therm mon i tor i n g fu n c ti o n . 2. s e l e c t t h e d e si re d fa n b e hav i or f o r therm ev e n t s . s e t t in g bi t 2 (b o o st b i t) o f c o nf igura t io n re g i st er 3 (reg. 0x78) ca u s es al l fa n s t o r u n a t 100 % d u ty c y c l e wh en ev e r therm is ass e r t e d . this a l lo ws fa i l -s a f e sy s t co olin g. i f t h is b i t = 0, t h e fa n s r u n a t t h eir c u r r en t s e t an d are not af fe c t e d b y e m t in gs therm ev e n t s . 3. se l e c t w h e t h e r therm e v en ts shou l d gener a t e sm b a l e r t in t e rr u p ts. b i t 5 (f4p) o f m a s k reg i st er 2 (reg. 0x75), w h en s e t , m a out s k s sm b a l e r t s w h e n t h e therm l i mi t va l u e i s exc e e d e d . th is b i t sh ou l d b e cle a r e d if sm b a l e r t s bas e d on t h e r m e v en ts a r e r e q u i r e d . 4. s e le ct a s u i t a b le therm l i m i t v a l u e . this va l u e de t e r m i n es w h et h e r a n sm b a l e r t is gen e ra t e d on t h e f i r s t therm a s s e r t i o n , or on ly i f a c u m u l a t i ve therm ass e r t io n t i me l i mi t is exce e d e d . a va l u e o f 0x 0 0 ca us es an sm b a l e r t to b e ge ne r a te d on t h e f i rst therm ass e r t io n. 5. se l e c t a therm monit o rin g time. this is h o w o f t e n os o r b i os l e v e l s o f t wa r e ch e c ks t h e therm timer . f o r exa m p l e , b i os co u l d r e ad t h e therm t i me r onc e an h o u r to de te r m i n e t h e c u m u l a t i v e therm a s se r t i o n tim e . i f , f o r e x a m p l e , th e t o tal therm ass e r t io n tim e is <22.76 m s in h o ur 1, >182.08 m s in h o ur 2, a n d >5.825 s in h o u r 3, this ca n in dica t e tha t sys t em p e r f o r - a m n ce is deg r a d i n g sig n if ican t l y sin c e therm is ass e r t in g m o r e f r eq uen t l y o n a n h o url y b a sis. al ter n a t i v e l y , o s o r b i os lev e l s o f t wa r e ca n t i m e -s tam p w h en t h e sys t e m is p o wer e d on. i f an sm b a l e r t is g e n e ra t e d d u e to t h e therm l i m i t b e i n g e x ceed ed , a n o t h e r t i m e - s t a m p can b e t a ke n. t h e dif f er en c e in t i m e ca n be calc u l a t e d f o r a f i xed therm limi t t i m e . f o r exa m ple , if i t t a k e s o n e w e ek fo r a therm limi t o configuring the a d t7460 therm pin as an out p ut i n addi tion t o t h e adt7460 b e in g a b l e t o m o ni t o r therm as a n in p u t, t h e ad t7460 c a n o p t i o n al l y dr i v e therm lo w a s a o u t p ut. th e us e r ca n p r ep r o g r a m sys t e m cr i t ic al t h er mal li m i i f t h e t e m p er a t u r e exce e d s a t h e r mal limi t b y 0.25c, n t s . t h e r m b o v e t h e t h er mal l i mi t o n as s e r t s lo w . i f t h e t e m p era t ur e is s t i l l a t h e ne x t mo n i to r i ng c y cl e, therm st a y s l o w . therm re m a i n s as s e r t e d lo w un til the t e m p er a t ur e is e q ual t o o r be lo w t h e t h er ma l l i mi t. si nce t h e t e m p er a t ure fo r t h a t channe l is m e asur e d on ly e v e r y mon i tor i ng c y cl e, on therm c e a s s e r t s , it i s g u ar an - te e d to r e ma i n l o w for a t l e a s t one mon i tor i ng c y cl e. th e therm p i n c a n b e co nf igure d t o ass e r t lo w if t h e r e m o t e 1, lo cal , o r rem o te 2 t e m p era t ur e therm l i m i t s a r e e x ceed ed b y 0.25c. th e therm limi t r e g i st ers a r e a t l o ca t i o n s 0x 6a, 0x6b , a nd 0x6c, r e s p ec ti ve l y . s e t t in g b i t 3 o f reg i s t ers 0x5f , 0x60, a n d 0x61 ena b les t h e therm o u tp u t fe a t u r e fo r t h e r e m o te 1 , l o c a l, and re mot e 2 t e m p er a t ur e cha n ne l s , resp e c t i vel y . fi g u r e 4 0 s h ow s h o w t h e therm p i n ass e r t s lo w as a n o u t p ut in t h e e v e n t o f a cr i t ical o v er t e m p era t ur e . f 2.914 s t o b e e x c e e d e d a n d th e n e x t ti m e i t ta k e s o n l y o n e h o u r , this in dic a t e s a s e r i o u s deg r ada t io n in sys t e m p e r f o r ma n c e . adt7460 monitoring cycle temp t h e r m l i m i t 0.25c therm 03228-040 f i gure 4 0 . a sser t i n g therm limit therm as an o u t p ut , b a s e d on t r ip p i ng therm lim i ts
adt7460 rev. c | page 27 of 52 fan drive using pwm control the adt7460 us es p u ls e wid t h m o d u la t i o n ( p wm) t o co n t rol fa n s p e e d . this r e lies o n va r y i n g t h e d u ty c y cle (o r o n /o f f ra t i o) o f a s q ua r e wa ve a p plie d to t h e fa n to va r y t h e f a n sp e e d . t h e e x te r n a l c i rc u i t r y re qu i r e d to d r ive a f a n u s i n g p w m c o n t ro l i s ext r em e l y si m p l e . a sin g l e nmos fet is t h e o n l y dr i v e de vice r e q u ir e d . the sp e c if ic a t io n s o f t h e mos f et d e p e n d on t h e maxim u m c u r r en t r e q u ir e d b y t h e fa n b e in g dr i v en. t y p i cal n o t e bo ok f a n s dra w a n o minal 1 70 ma, s o sot de vices ca n be us e d w h er e b o ar d s p ace is a con c er n. i n desk t o ps, fa n s can typ i c a l l y dra w 2 50 ma t o 3 0 0 s e ve r a l f a ns i n p a r a l l el f r om a s i ng l e p w m output or d r ive s la rger s e r v er fa n s , t h e mos f et n e e d s t o han d le t h e hig h er c u r r en t r e q u ir e m e n ts. t h e o n ly o t h e r st i p u l a t ion is t h a t t h e mo sf et s h ou l d ha v e a g a te e c t in ter f acing t o t h e pwm _ out pin. v gs ca n b e g r ea t e r n o o l t d e t h e a p plie d i m u m o p era t in g sp e e d o f t h e fan. - w i r e fan can b e dr i v en usin g pwm ma eac h . i f t h e us er dr i v es vol t age dr ive, v gs < 3.3 v , f o r dir tha n 3.3 v as lon g as t h e p u l l -u p o n the ga te is tied t o 5 v . th e s f e t sh ve a lo t an ce t o en s u r e tha t m o o u l d als o ha ica n t v w o n r e sis t h er e is r e d u c t s i g n if e v o l t ag a g e dr o p acr o s s t h e fet . this w o u l a c r o s s t h e fa n and , t h er efo r e , t h e max f i gur e 41 sh o w s h o w a 3 co n t r o l . adt7460 tach/ain tach pwm 12v fan q1 ndt3055l 3.3v 12v 12v 10k ? 4.7k ? 10k ? 10k ? 1n4148 03228-041 f i gure 4 1 . dri v i n g a 3- wi re f a n b y using a n n- cha n n e l mosfet f i gur e 41 us es a 10 k? p u l l -u p r e sis t o r f o r th e t a ch sig n al . t h i s a ssu me s t h a t t h e t a c h s i g n a l i s op e n - c o l l e c t or f r om t h e fa n. i n al l cas e s, th e t a ch sig n al f r o m th e f a n m u s t be k e p t b e lo w 5 v maxim u m t o p r ev en t da ma g i n g t h e adt7460. i f in dou b t a s to w h e t he r t h e f a n u s e d h a s an op e n - c ol l e c t or or tote m p o l e t a c h output , u s e o n e of t h e i n put s i g n a l c o n d i t i o n i n g cir c ui ts sho w n i n t h e f a n s p e e d m e asur em e n t s e c t io n. f i gur e 42 sh o w s a fa n dr i v e cir c ui t usin g an npn tra n sis t o r s u c h as a g e n e ra l-p u r p os e mmb t2222. w h ile t h es e de vices a r e i n e x p e ns iv e, t h e y te nd to h a v e m u ch l o we r c u r r e n t h a n d l i n g ca p a b i li t i es an d hig h er o n -r esis t a n c e t h a n mosfet s. w h en c h o o sin g a tra n sis t o r , ca r e sh o u ld b e tak e n t o e n s u r e tha t i t m e e t s t h e fan s c u r r en t r e q u ir e m en ts. en s u r e tha t t h e ba se r e si s t o r i s c h osen s u c h th a t th e tra n si s t o r i s s a t u r a te d w h e n t h e fa n is p o w e re d o n . adt7460 tach/ain tach 12v fan 3.3v 12v 12v 470 ? 4.7k ? 10k ? 1n4148 pwm q1 mmbt2222 03228-042 10k ? f i g u re 42. d r iv ing a 3 - wire f a n by u s i n g an npn t r ans i s t or driving two f a ns fro m pw m3 n o t e t h a t the ad t7460 has f o u r t a ch in p u ts a v a i la b l e f o r fa n s p eed m e a s ur em en t , b u t o n l y th r e e p w m d r i v e o u t p u t s . i f a f o ur th fa n is bein g us ed in t h e s y s t em, i t sh o u ld be dr i v en f r o m th e pw m 3 o u t p u t i n pa ra lle l w i th th e th i r d fa n . f i g u r e 43 s h o w s how to dr ive two f a ns in p a r a l l e l u s ing l o w c o st np n tra n si s t o r s. f i gur e 44 is t h e eq ui v a l e n t ci r c ui t usi n g t h e n d t3055l mo s f et . n o t e t h a t since th e m o s f et can han d le u p t o 3.5 a, i t is sim p ly a ma t t er o f co nn ec t i n g an o t h e r fa n dir e c t l y in p a ral l e l wi th t h e fi r s t . c a r e sh o u ld b e tak e ts wi th tra n sist o r s a n d fe t s t o e n s u r e tha r e q u i r ed t o so u r ce c u r r en t an d t h a t t h e y sin k less t h n t h e 8 ma max i m u m c u r r en t s p eci f i e d p r o - g r a m m e d t o s y n c h r o n i z e ta c h 2 , ta c h 3 , a n d ta c h 4 t o t h e pwm3 o u t p u t . this al lo ws p w m3 t o dr i v e tw o o r thr e e fa n s . i n t h i s cas e , t h e dr iv e circ u i t r y lo oks t h e s a me as sho w n i n f i gure 4 2 , f i gur e 43, an d f i gur e 44. th e s y n c b i t in reg i s t er 0x62 ena b les th i s fun c t i o n . n in desig n in g dr i v e c i r c ui t th e pwm p i n s a r e n o t a o n t h e da ta s h ee t . driving up to thre e f a ns fro m pwm2 t a ch m e a s ur em en t s f o r fa n s a r e s y n c h r o n iz e d t o pa r t i c ul a r p w m chan nel s , fo r exam ple, t a ch 1 i s s y n c hr oni z e d t o p w m1 . ta c h 3 a n d ta c h 4 a r e b o t h s y n c h r o n i z e d t o p w m 3 , s o pwm3 can dr i v e tw o fa ns. a l te r n a t i vely , pwm 3 ca n b e
adt7460 rev. c | page 28 of 52 adt7460 pwm3 3.3v 3.3v 12v 4148 03228-043 1n q1 mmbt3904 q2 mmbt2222 q3 mmbt2222 10 ? 10 ? 2.2k ? 1k ? tach3 f i gure 4 3 . int e r f acing t w o f a ns i n p a r a ll el to the pw m tach4 3 o u tput usi n g l o w c o st np n t r a n s i st or s adt7460 pwm3 tach3 tach4 3.3v 3.3v 3.3v +v +v 03228-044 tach tach q1 ndt3055l 1n4148 5v or 12v fan 5v or 12v fan 10k ? typical 10k ? typical 10k ? typical a l l e l t o t h e p w m o sfe t f i g u re 44. inte r f a c i n g t w o f a ns in p a r 3 o u t p ut u s ing a s i n g le n- ch anne l m table 29. s y n c : e n hance ac oustics registe r 1 (reg. 0x62) bit mnemonic description <4> sync 1 synchronizes tach2, tach3, and tach4 to pwm 3 . i n t o a v o l t a g e . t h is is ac-c o u ple d i n t o t h e adt7460 thr o u g h t h e 0.01 f c a p a ci t o r . o n -c hi p sig n al con - di t i onin g a l lo ws acc u r a te m o n i to r i n g o f fa n sp e e d . t h e va l u e o f r sense ch o s e n de p e nds o n t h e p r o g r a mm e d in p u t t h r e sh old an d on t h e c u r r e n t d r aw n b y t h e f a n . for f a n s d r aw i n g a ppr ox i m at e l y 200 ma, a 2 ? r sense val u e is sui t a b l e w h en t h e thr e sh old is p r og ra mm ed as 40 mv . f o r fa ns tha t dra w m o re c u r r en t, s u ch as la rg er des k t o p o r s e r v er fa n s , r sense ma y b e r e d u ce d fo r t h e s a m e p r og ra mm e d thr e sh old . the smal ler t h e thr e s h ol d p r o- g r a m m e d t h e b e t t er , si nce m o r e v o l t a g e is de velo p e d acr o s s t h e h e driving 2-wire fans f i gur e 45 sh o w s h o w a 2-wir e fan ma y be co nn e c t e d t o t h e adt7460. this cir c ui t al lo ws t h e s p ee d o f a 2-wir e fa n t o be m e a s ur e d , e v en t h o u g h t h e f a n has n o de di ca te d t a ch sig n a l . a s e r i es r e sis t o r , r sense , in t h e fan cir c ui t co n v er ts t h e fan co mm u t a t ion pu ls e s f a n a n d t h e f a n spi n s f a ste r . fi g u re 4 6 show s a t y pi c a l pl ot of t s e n s in g wa v e f o r m a t a t a ch /ain p i n. th e m o s t im p o r t a n t th i n g i s th a t th e v o l t a g e s p ik es (e i t h e r n e ga t i v e g o i n g o r posi ti v e g o in g ) a r e m o r e th a n 4 0 m v in a m p l i t u d e . t h i s all o w s f a n s p eed to b e rel i ably de te r m i n e d . 03228-045 adt7460 pwm tach/ain 5v or 12v fan 3.3v q1 ndt3055l +v 10k ? typical 1n4148 0.01 f r sense 2 ? g a 2 - wire f a n typical f i g u re 45. d r iv i n
adt7460 rev. c | page 29 of 52 03228-046 ch2 5.00mv ch1 100mv m 4.00ms a ch1 ?2.00mv ch3 50.0mv ? @: : 250 mv ? 258mv ch4 50.0mv t ?1.00000ms laying out 2- wire an d 3-wi re f a ns o n c i r c ui t a r ra n g em en t f i gure 46. f a n spee d s e ns ing w a vefor m at t a ch/ain p i n f i gur e 47 sh o w s h o w t o l a y o u t a co mm f o r 2-wi r e a n d 3-wi r e fa n s . s o m e co m p o n en t s a r e n o t po p u la t e d , dep e ndi n g o n w h et h e r a 2- wir e o r 3-wir e fan is us e d . 3.3v or 5v tach/ain p w m 12v or 5v q1 mmbt2222 r4 r5 r3 c1 r2 r1 f o r 2 - w i r e f a n s : e r 4 , c 1 u n p o p u l a t p o p u l a t r 1 , r 2 , r 3 e d 1n4148 e f a n s : r 1 , r 2 , r 3 p u l a t e d f i g u re 47. pl ann i ng f o r 2- wi r e or 3-w i re f a ns on a pc b m e n t . g e. i gur e 48 t o f i g u r e 51 s h o w circ ui ts f o r m o s t c o mm on fa n ta c h o u t p u t s . the fa n t a c h o u t p u t has a resis t i v e p u l l -u p t o v cc , i t can be nn e c te d dir e c t ly to t h e fan i n p u t, as sho w n i n f i gur e 48. 03228-047 f o r 3 - w i r p o p u l a t e r4 = 0 ? c 1 = u n p o tach inputs p i n s 4 , 6 , 7 , a n d 9 a r e o p en-dra in t a ch in p u ts f o r fa n s p eed me a s u r e s i g n al con d i t ionin g in t h e adt7460 acco mmo d a t es t h e s l o w r i s e a nd fal l t i mes typ i c a l o f fa n t a ch omet er o u t p u t s. the maxi- m u m in p u t sig n al ra n g e is 0 v to 5 v , e v en w h e r e v cc is less t h a n 5 v . i n t h e e v en t t h a t t h es e in p u ts a r e s u p p l i e d f r o m fa n o u t p u t s th a t e x ceed 0 v t o 5 v , ei t h e r r e s i s t i v e a t t e n u a t i o n o f t h e fa n sig n al o r dio d e c l am p i n g m u s t be in c l ude d t o k e ep in p u ts wi t h i n an accept a b le ra n f i f co 12v v cc 03228-048 pull-up 4.7k ? typical tach output fan speed counter tach adt7460 u t has a r e sis t i v e p u l l -u p t o 12 v (o r o t h e r v o l t a g e c l a m p e d wi th a z e n e r r dio d e v o l t a g e sh o u l d be gr ea t e r t h a n v o f t h e t a ch in p u t b u t les s th a n 5 v , a l lo win g z e n e r . a val u e o f b e tw e e n 3 v f i gure 48. f a n w i th t a ch p u ll-up t o v cc i f the fa n ou t p g r ea t e r tha n 5 v), th e fan o u t p u t ca n b e dio d e , as sho w n in f i gur e 49. th e z e n e ih fo r t h e v o l t a g e tolera n c e o f t h e a nd 5 v is su i t ab le. 12v v cc 03228-049 pull-up 4.7k ? typical tach output fan speed counter tach adt7460 zd1* *choose zd1 voltage approximately 0.8 v cc f i gure 49. f a n w i th t a ch p u ll-up t o v o ltage . 5 v , for exa m pl e , 1 2 v , clamp e d with z e n e r d i od e i f the fa n has a str o n g p u l l -u p (les s tha n 1 k?) to 12 v o r a to tem - p o le o u t p u t , a s e r i es r e sisto r ca n b e a dde d to lim i t t h e l d b e c h a t < up i n p u t r e 0 k ? t o t h ke n i n a t i n g s i stor v a lu e s . u i t a b le val u es f o r r1 a n d r2 w nd ? . t h i s g i ves a hig h in p u t v z e n e r c u r r en t, as s h o w n in f i gu r e 50. al t e r n a t i v e l y , a r e sis t i ve a tte n u a t or ma y b e u s e d , a s s h o w n i n f i gur e 51 . r1 a nd r2 s h o u h o s e n su c h t 2 v v pull up r2 /( r pull + r1 + r2 ) < 5 v t h e f a n g r ou nd. u ts ha v e an in p i s sh ou l d b e t a sis t a n c e o f n o minal l y 1 6 to a c c o u n t w h e n c a l c u l r e w i t h a pu l l - u p volt age of 1 2 v an s i stor l e ss t h an d pu l l - u p re 1 k?, s 4 7 k o u l d be 10 0 k? a o l t a g e o f 3.83 v . 5 v o r 1 2 v v cc pull-up typ ? 03228-050 <1k or totem pole tach output counter t a c h fan speed adt7460 zd1 zener* *choose zd1 voltage approximately 0.8 v cc f i gure 50. f a n w i th str o ng t a c h p u ll-u p to > v f a n r1 t , cl am p e d wi th z e ner a n d resi sto r 10k ? cc o r t o te m - p o l e o u t p u
adt7460 rev. c | page 30 of 52 12v v cc 03228-051 <1k ? tach output fan speed counter t a c h a d t 7 4 6 0 r2* *see text r1* f i g u r e w i th str o fan sp ee d me as ur e e f a n e r do es n dir e c t l y bec a us e th e f a w o u l d t a k e s e ve r a l s e c a c c o u n t. i n m e a s ur e d b y ga t i n g a n of a 1 6 - bit c o u n te r f o r ( f i g u r e 5 2 ) . t h e a c c u m n t i s a c tu a l ly prop or t i on a l to e f a n t a c h om e t e r p e r i o d a n d i n ve r s ely prop or t i on a l to t h e f a n 5 1 . f a n n g t a c h p u ll-u p to > v cc or t o t e m-p o le output, at tenuat ed w i t h r 1 /r 2 m ent t h c o un t o t co u n t t h e fa n t a ch ou t p ut p u ls es n s p ee d ma y b e les s than 1000 rpm. i t o nds to a c c u m u l a te a r e a s o n a b ly la rge a n d u r a t e c ste a d , t h e p e r i o d o f t h e fan r e vol u t i o n i s o n -chi p 90 khz os ci l l a t o r in t o t h e in pu t n p e r i o d s of t h e f a n t a c h output u l a te d c o u t h sp e e d. 1 2 3 4 cloc k pwm t a c h 03228-052 f i gure 5 2 u r e m ent , t h e n u m b er o f p u ls es co un t e d , is det e r m in e d b y t h e s e t t in g s f reg i s t er 0x7b (fa n p u ls es p e r r e v o l u tio n r e g i s t er). this s t w o b i ts fo r e a ch fa n, a l lo win g o n e , tw o . f a n spee d m e a s n o r e g i st er co n t a i n (defa u l t ), t h r e e , o r f o ur t a ch p u ls es t o be co u n t e d . the fan t a ch omet er r e adin gs a r e 16-b i t va l u es c o n s is t i n g o f a 2-b y te r e ad f r o m t h e ad t746 0. table 30. fan s p ee d measurement registers register description d e f a u l t 0x28 tach1 low byte 0x00 0x29 tach1 high byte 0x00 0x2a tach2 low byte 0x00 0x2b t a c h 2 h i g h b y t e 0x00 0x2c tach3 low byte 0x00 0x2d tach3 high byte 0x00 0x2e tach4 low byte 0x00 0x2f tach4 high byte 0x00 reading f a n speed from the adt7460 i f fa n sp e e d s a r e b e i n g m e asur e d , t h is i n volves a 2-r e g i ster r e ad r ea c h m e a s ur e m en t . th e l o w b y t e s h o u l d be r e a d f i r s t . t h i s us es t h e hig h b y t e t o b e f r oze n un t i l b o t h hig h an d lo w b y te . e t er r e a d 11.11 s p e r i o d c l o c k s ( 9 a t o r ) ga t e d t o th e fa n sp ee d un t e r , o m t h e r i sin g e u ls e t o t h e i sin g e d e o f t h e t h ir d fa ( a s s u m i n g tw o p u ls es e r r e v o t i o n ar e b e i n g c e i s e s s e n t ial l y e as ur i h e f a n t a c h g h er t h e co un t val u e t h e w er t ac t u a l ly b i t fa n t a ch om e t er e ad in g 0xff ff in dica h a t t h e fan has s t alled o r t i t i s u nning v e r y s l o r p m ) . i g h l i m i t : > c o m p ar i s on p e r f or me d e ing m e a s ur e d , exce e d ing e f o ca r e g i st ers a r e re ad f r om. this p r e v e n t s er r o n e o u s t a c h re adi n gs t h e f a n t a ch o m i n g r e g i s t ers r e p o r t t h e n u m b er o f 0 k h z os cil l co f r d g e of t h e f i rs t fa n t a c h p r g n t a c h p u ls e p l u c o un t e d). si n c e t h e de v i m n g t p e r i o d , t h e h i slo h e fan is r u n n i n g . a 1 6 - r o f t e s ei t h e r t tha r w l y ( < 1 0 0 h since t h e ac t u a l fa n t a ch p e r i o d is b a fa n t a ch li m i t b y 1 s e ts t h e a p p r o p r i a t e st a t u s b i t and can b us ed t o g e n e ra te a n sm b a l e r t . the fan t a ch l i mi t r e g i s t ers a r e 16-b i t va l u es c o n s is t i n g o f tw o by t e s . table 31. fan t a c h l i m i t r e gisters t register description d e f a u l 0x54 tach1 minimum low byte 0xff 0x55 tach1 minimum high byte 0xff 0x56 tach2 minimum low byte 0xff 0x57 t a c h 2 m i n i m u m h i g h b y t e 0xff 0 x 5 8 m y t e 0xff t a c h 3 i n i m u m l o w b 0 x 5 9 t a c h 3 m i n i m u m h i g h b y t e 0xff 0x5a t a c h 4 m i n i m u m l o w b y t e 0xff 0x5b tach4 minimum high byte 0xff fan sp ee d me as ur em ent r a te the fan t a ch r e adin gs a r e n o r m al l y u p da t e d o n ce e v er y sec o n d . the f a s t b i t (bi t 3) o f c o nf igu r a t io n reg i st er 3 ( r e when s e t, u p da tes th e g . 0 x 7 8 ) , fa gs ev er y 250 m s . f s a r e n o y a p w m cha nnel b u t r e in ste p o wer e d dir o r 12 v , i t s ass o c i a t e d dc i t in c o f igura t io n r e b e s e t. th is a l lo ws t a ch e adin gs o b e t a k e n o n a s i s f o r fa n s co nn ec t e d e c t ly to a dc s o ur ce. n t a ch r e adin i f a n y o t h e f a n t b e in g dr i v en b a a d e c t ly f r o m 5 v b n g i ster 3 sh o u l d r t a c o n t in uo u s b dir
adt7460 rev. c | page 31 of 52 ed 43d an moothest graph ermines the correct pulses/revolution e. 32. fan pulses per re tion register (reg. 0x7b) description calculating fan spe assuming a fan with a two pulses/revolution (and two pulses/ revolution being measured), fan speed is calculated by fan speed (rpm) = 90,000 60/ fan tach reading where: fan tach reading = 16- bit fan tachometer reading for example: tach1 high byte (reg. 0x29) = 0x17 tach1 low byte (reg. 0x28) = 0xff what is fan 1 speed in rpm? fan 1 tach reading = 0x17ff = 61 rpm = (f 60)/fan 1 tach reading rpm = (90000 60)/6143 fan speed = 879 rpm fan pulses per revolution different fan models can output either 1, 2, 3, or 4 tach pulses per revolution. once the number of fan tach pulses is deter- mined, it can be programmed into the fan pulses per revolution register (reg. 0x7b) for each fan. alternatively, this register c be used to determine the number of pulses/revolution output by nts at 100% speed a given fan. by plotting fan speed measureme with different pulses/revolution settings, the s with the lowest ripple det valu table bit mnemonic volu <1:0> fan1 default 2 pulses per revolution <3:2> fan2 default 2 pulses per revolution <5:4> fan3 default 2 pulses per revolution <7:6> fan4 default 2 pulses per revolution table 33. fan pulses per revo lution register bit values value description 00 1 pulse per revolution 01 2 pulses per revolution 10 3 pulses per revolution 11 s per revolution 4 pulse 2-wire fan speed measuremen ts the adt7460 is capable of measuring the speed of 2-wire fans, ch outputs. to do this, the fan must be ry section. in this med as analog g. 0x73) nemon tion that is, fans without ta interfaced as shown in the fan drive circuit case, the tach inputs need to be reprogram inputs, ain. table 34. configuration register 2 (re bit m ic descrip 3 ain4 at pin 9 is to speed of a 2-wire fan using ensing res ling 1 indicates th reconfigured measure the an external s capacitor. istor and coup 2 ain3 1 indicates that pin 4 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. 1 ain2 1 indicates that pin 7 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. 0 ain1 1 indicates that pin 6 is reconfigured to measure the speed of a 2-wire fan using an external sensing resistor and coupling capacitor. ain switching threshold having configured the tach inputs as ain inputs for 2-wire measurements, the user can select the sensing threshold for the ain signal. t bit mnemonic description able 35. configuration register 4 (reg. 0x7d) <3:2> ainl these two bits defin e the input threshold for 2-wire fan speed measurements. 00 = 20 mv 01 = 40 mv 10 = 80 mv 11 = 130 mv fan spin-up the adt7460 has a unique fan spin-up function. it spins the fan at 100% pwm duty cycle until two tach pulses are detected on the tach input. once two pulses are detected, the pwm duty cycle goes to the expected running value, for example, 33%. the advantage of this is that fans have different spin-up characteristics and take different amounts of time to overcome inertia. the adt7460 runs the fans just fast enough to overcome inertia and is quieter on spin-up than fans programmed to spinup for a given spin-up time. fan start-up timeout to prevent false interrupts being generated as a fan spins up (since it is below running speed), the adt7460 includes a fan start-up timeout function. this is the time limit allowed for two tach pulses to be detected on spin-up. for example, if 2 seconds fan start-up timeout is chosen and no tach pulses occur within 2 seconds of the start of spin-up, a fan fault is detected and flagged in the interrupt status registers.
adt7460 rev. c | page 32 of 52 figuration (reg. 0x5cC0x5e) table 36. pwm1Cpwm3 con bit mnemonic description <2:0> spin these bits control the start-up timeout for pwm1. 000 = no start-up timeout 001 = 100 ms 010 = 250 ms (default) 011 = 400 ms 100 = 667 ms 101 = 1 s 110 = 2 s 111 = 4 s d isabling fan start-up timeout although fan start-up makes fan spin-ups much quieter than fixed-time spin-ups, the option exists to use fixed spin-up times. bit 5 (fspdis) = 1 in configuration register 1 (reg. 0x40) disables the spin-up for two tach pulses. instead, the fan spins up for the fixed time as selected in registers 0x5c to 0x5e. pwm logic state the pwm outputs can be programmed high for 100% duty cycle (noninverted) or low for 100% duty cycle (inverted). table 37. pwm1Cpwm3 configuration (reg. 0x5cC0x5e) bits bit mnemonic description <4> inv 0 = logic high for 100% pwm duty cycle 1 = logic low for 100% pwm duty cycle pwm drive frequency the pwm drive frequency can be adjusted for the application. registers 0x5f to 0x61 configure the pwm frequency for pwm1 to pwm3, respectively. table 38. pwm1 to pwm3 frequency registers (reg. 0x5f to 0x61) bit mnemonic description <2:0> freq 000 = 11.0 hz 001 = 14.7 hz 010 = 22.1 hz 011 = 29.4 hz 100 = 35.3 hz (default) 101 = 44.1 hz 110 = 58.8 hz 111 = 88.2 hz fan speed control n speed by two different modes. ed control mode. in this mode, fan e c fan speed control loop. for more information on how to program the automatic fan speed control loop and dynamic min calibration, see the an-613 programming the automatic fan speed control loop application note ( http://www.analog.com/uploaded files/application_notes/ 331085006an613_0.pdf). the second fan speed control method is manual fan speed control, which is described next. manual fan speed control the adt7460 allows the duty cycle of any pwm output to be manually adjusted. this can be useful if you want to change fan speed in software or if you want to adjust pwm duty cycle output for test purposes. bits <7:5> of registers 0x5c, 0x5e (pwm configuration) control the behavior of each pwm output. table 39. pwm1 to pwm3 configuration (reg. 0x5cC0x5e) bits bit mnemonic description the adt7460 can control fa the first is automatic fan spe speed is automatically varied with temperature and without cpu intervention, once initial parameters are set up. the advantage of this is that, in the case of the system hanging, th system is protected from overheating. the automatic fan speed control incorporates a feature called dynamic t min calibration. this feature reduces the design effort required to program the automati t <7:5> bhvr 111 manual mode once under manual control, each pwm output can be manually updated by writing to registers 0x30, 0x32 (pwmx current duty cycle registers). programming the pwm current duty cycle registers the pwm current duty cycle registers are 8-bit registers, which allow the pwm duty cycle for each output to be set anywhere from 0% (0x00) to 100% (0xff) in steps of 0.39% (256 steps). the value to be programmed into the pwmmin register is given by value (decimal) = pwm min /0.39 example 1: for a pwm duty cycle of 50%, value (decimal) = 50/0.39 = 128d value = 128d or 0x80. example 2: for a pwm duty cycle of 33%, value (decimal) = 33/0.39 = 85d value = 85d or 0x54.
adt7460 rev. c | page 33 of 52 a u l t table 40. pw m dut y c y cle registers register description d e f 0 x 3 0 pwm1 duty cycle 0xff (100%) 0x31 p w m 2 d u t y c y c l e 0xff (100%) 0x32 p w m 3 d u t y c y c l e 0xff (100%) by r e adin h e c y c l e g i s t ers, us e r s c t r ack o f t h y cle o n e a p w m o u t p u t v en t h e fa n s a t i c f s p e e d n t r o l o de a c o i c e o d e . g t pwmx c u r r en t d u t y r e a n k e e p e c u r r en t d u t y c c h , e w h e n r e r u nnin g i n a u to ma a n c o m o r i n u s t n h a n c em en t m v a ry p w m d u t y c y c l e w i t h 8 - b i t r e s o l u t i o n 03228-053 f i g u re 5 o n t r m a nua lly w a r e s o i on of 0 % operat ing from 3.3 v stan dby a d t 6 0 e s i g to o t e f r a s t by s u p t s u p r t s 3 s 5 s es , r e v e s o r is lo w e r i n t h e s t a t e s h e a m de , lo w e r i n h e co r o l t a g e f r o c e w t h e cpu t e m a t ur nd cha e y namics o mic t m in co n t r o i s e 3 . c o l pw m d u t y c y c l e i t h l u t . 3 9 t h e 7 4 h a s b e e n s p ecif ical l y d n ed p e r a o m 3 . 3 v p l y . i n com p u t ers tha p o a n d t a t t h e co o l t a g o f t h e p r o c e s e d s e . i f usin g t d y n i c t m i n m o g t e v o t h e p s s o r o u l d cha n g e p er e a n g t h e d f t h e sys t em u n der d y na l . lik e w , wh en m o ni t o ri n g therm , t h e h e r m t t i m e r s u ld i s a bl e r xnor tree test mo de the adt7460 in c l udes a n xno r tr ee t e s t m o de . this m o de is us ef u l fo r in-cir c u i t t e st e q u i pmen t a t b o a r d-le ve l t e st ing. by a p p l yi n g s t im ul us t o th e p i n s in c l ud ed i n t h e xn o r tr ee , i t i s p l e te c s or s h or h e s y ard. f u r e 54 sh o w s t i g n als t h a e exer cis t h e xn r t r e e t mo d t xn tr ee t t i s in v o k e d t in g b en ) o h e xn o r t t e s t ena b le r e g i st er (re g . 0 x 6 f ) h o b e d d du i ng t h e s e s t a t e s . o ss i b to d e t op e n t s on t ste m b o i g h e s t a r e d i n o e s t e . h e o r e s b y set i t 0 ( x f t r e e . pwm1/xto pwm3 pwm2 tach 4 tach3 tach2 tach1 03228-054 f i gure 54. x ee t e s t power-on defaul t the adt7460 do es n o t m o ni to r t e m p era t u d fa n s p ee d b y d t o w e r o ni to r i n e m p er a n d f a e d i le e t t h e st a r t b i o nf i g u n r e g i st r 1 ( t 0, a r es s 0x40) t o 1. th e s r u n a t f e e d o n o w e r - u b e ca us t h e bh vr b ( b i t s < 7 t h e p w mx c i g u r n r e g ers a r e s e t t 0 0 ( f a n s r l l s p eed) b y defa u l t. n o r t r r e a n e f a u l n p o - u p . m g o f t a t u r e n s p e s e n a b d b y s i n g t t i n c r a t i o e b i d d f a n u l l s p p p . this is e i t s : 5 > ) i n o nf a t io i s t o 1 u n f u
adt7460 rev. c | page 34 of 52 e 41 t ss 7 6 5 4 t 3 2 1 0 lt able? adt7460 register summary tabl . ad 7460 registers addre r/w description bit bit bit bit bi bit bit bit defau lock 0x20 r 2.5 v reading 9 8 7 6 5 4 3 2 0x00 0x22 r v cc reading 9 8 7 6 5 4 3 2 0x00 0x25 r remote 1 temperature 9 8 7 6 5 4 3 2 0x80 0x26 r local temperature 9 8 7 6 5 4 3 2 0x80 0x27 r remote 2 temperature 9 8 7 6 5 4 3 2 0x80 0x28 r low byte 7 6 5 4 3 2 1 0 0x00 tach1 0x29 r tach1 high byte 15 14 13 12 11 10 9 8 0x00 0x2a r tach2 low byte 7 6 5 4 3 2 1 0 0x00 0x2b r tach2 high byte 15 14 13 12 11 10 9 8 0x00 0x2c r tach3 low byte 7 6 5 4 3 2 1 0 0x00 0x2d r tach3 high byte 15 14 13 12 11 10 9 8 0x00 0x2e r tach4 low byte 7 6 5 4 3 2 1 0 0x00 0x2f r tach4 high byte 15 14 13 12 11 10 9 8 0x00 0x30 r/w pwm1 current duty cyc le 7 6 5 4 3 2 1 0 0xff 0x31 r/w pwm2 current duty cycle 7 6 5 4 3 2 1 0 0xff 0x32 r/w pwm3 current duty cycle 7 6 5 4 3 2 1 0 0xff 0x33 r/w remote 1 operating point 7 6 5 4 3 2 1 0 0x64 yes 0x34 r/w local temp operating point es 7 6 5 4 3 2 1 0 0x64 y 0x35 r/w remote 2 operating point 7 6 5 4 3 2 1 0 0x64 y es 0x36 r/w dynamic t min control reg. 1 2 s r2t lt r1t phtr phtl phtr1 v cc re cyr2 0x00 yes 0x37 r/w dynamic t min co ntrol reg. 2 cyr2 c yr 2 cyl cyl cyl cyr1 cyr1 c yr1 0x00 yes 0x3d r device id regist er 1 7 6 5 4 3 2 0 0x27 0x3e r company id numbe r 7 6 5 4 3 2 1 0 0x41 0x 3f r revision number ver ver ver ver stp stp stp stp 0x62 or 0x6a 0x 40 r/w configuration register 1 v cc todis fspdis res fspd rdy lock strt 0x00 yes 0x41 r interrupt status register 1 ool r2t lt r1t res v cc res 2.5v 0x00 0x42 r interrupt status register 2 d2 d1 5 fa n3 fan2 fan1 ovt res 0x00 0x44 r/w 2.5 v l t 5 4 3 2 1 0 0x00 ow limi 7 6 0x45 r/w 2.5 v h 3 2 1 0 0xff igh limit 7 6 5 4 0x48 r/w v cc low 0 0x00 limit 7 6 5 4 3 2 1 0x49 r/w v cc hig 0 0xff h limit 7 6 5 4 3 2 1 0x4e r/w remote 1 temp low limit 7 6 5 4 3 2 1 0 0x81 0x4f r/w remote 1 temp high limit 7 6 5 4 3 2 1 0 0x7f 0x50 r/w local temp low limit 7 6 5 4 3 2 1 0 0x81 0x51 r/w local temp high limit 7 6 5 4 3 2 1 0 0x7f 0x52 r/w remote 2 temp low limit 7 6 5 4 3 2 1 0 0x81 0x53 r/w remote 2 temp high limit 7 6 5 4 3 2 1 0 0x7f 0x 54 r/w tach1 minimum low byte 7 6 5 4 3 2 1 0 0xff 0x55 r/w tach1 minimum high byte 15 14 13 12 11 10 9 8 0xff 0x 56 r/w tach2 minimum low byte 7 6 5 4 3 2 1 0 0xff 0x57 r/w tach2 minimum high byte 15 14 13 12 11 10 9 8 0xff 0x58 r/w tach3 minimum low byte 7 6 5 4 3 2 1 0 0xff 0x59 r/w tac h3 m high byte 13 12 11 10 9 8 0xff minimu 15 14 0x5a r/w tach4 byte 1 0 0xff minimum low 7 6 5 4 3 2 0x5b r/w tach4 byte 9 8 0xff minimum high 15 14 13 12 11 10 0x5c r/w pwm1 registe spin spin 0x62 yes configuration r bhvr bhvr bhvr inv slow spin 0x5d r/w pwm2 configuration register bhvr bhvr bhvr inv slow spin spin spin 0x62 yes 0x5e r/w pwm3 configuration register bhvr bhvr bhvr inv slow spin spin spin 0x62 yes 0x5f r/w remote 1 t range /pwm 1 freq. range range range range thrm freq freq freq 0xc4 yes 0x60 r/w local t range /pwm 2 freq. range range range range thrm freq freq freq 0xc4 yes 0x61 r/w remote 2 t range /pwm 3 freq. range range range range thrm freq freq freq 0xc4 yes 0x62 r/w enhance acoustics reg. 1 min3 min2 min1 sync en1 acou acou acou 0x00 yes 0x63 r/w enhance acoustics reg. 2 en2 acou2 acou2 acou2 en3 acou3 acou3 acou3 0x00 yes 0x64 r/w pwm1 min duty cycle 7 6 5 4 3 2 1 0 0x80 yes 0x65 r/w pwm2 min duty cycle 7 6 5 4 3 2 1 0 0x80 yes 0x66 r/w pwm3 min duty cycle 7 6 5 4 3 2 1 0 0x80 yes
adt7460 rev. c | page 35 of 52 3 bit 2 bit 1 bit 0 default lockable? address r/w description bit 7 bit 6 bit 5 bit 4 bit 0x67 r/w rem ote 1 tem 7 6 5 4 3 2 1 0 0x5a yes p t min 0x68 r/w local temp t min 7 6 5 4 3 2 1 0 0x5a yes 0x69 r/w remote 2 tem 7 6 5 4 3 2 1 0 0x5a yes p t min 0x6a r/w remote 1 th erm limit 7 6 5 4 3 2 1 0 0x64 yes 0x6b r/w local therm 7 6 5 4 3 2 1 0 0x64 yes limit 0x6c r/w remote 2 th erm limit 7 6 5 4 3 2 1 0 0x64 yes 0x6d r/w remote 1 loc hysr1 h ysl hysl hysl hysl 0x44 yes al hyster esis ysr1 hysr1 hysr1 h 0x6e r/w remote 2 tem hysr2 h res res res 0x40 yes p hysteresis ysr2 hysr2 hysr2 res 0x6f r/w xnor tree te res res res res res res res xen 0x00 yes st enable 0x70 r/w remote 1 tem offset 7 6 5 4 3 2 1 0 0x00 yes perature 0x71 r/w local temperature o ffset 7 6 5 4 3 2 1 0 0x00 yes 0x72 r/w remote 2 temperature offset 7 6 5 4 3 2 1 0 0x00 yes 0x73 r/w configuration register 2 shdn conv attn avg ain4 ain3 ain2 ain1 0x00 yes 0x74 r/w interrupt mask register 1 ool r2t lt r1t res v cc res 2.5v 0x00 0x75 r/w interrupt mask register 2 d2 d1 f4p fan3 fan2 fan1 ovt res 0x00 0x76 r/w extended resolution 1 res res v cc v cc res res 2.5v 2.5v 0x00 0x77 r/w extended resolution 2 tdm2 tdm2 ltmp ltmp tdm1 tdm1 res res 0x00 0x78 r/w configuration register 3 dc4 dc3 dc2 dc1 fast boost therm enable alert 0x00 yes 0x79 r therm status register tmr tmr tmr tmr tmr tmr tmr asrt/ tmr 0x00 0x7a r/w therm limit register limt limt limt limt limt limt limt limt 0x00 0x7b r/w fan pulses per revolu tion fan4 fan4 fan3 fan3 fan2 fan2 fan1 fan1 0x55 0x7d r/w configuration register 4 res re s res res ainl ainl res al2.5v 0x00 yes 0x7e r test register 1 do not write to these registers 0x00 yes 0x7f not write to these registers 0x00 yes r test register 2 do t able 42. voltage reading registers (power-on default = 0x00) egister address r/w description r 0x20 read-only 2.5 v reading (8 msbs of reading) 0x22 read-only v cc reading: measures v through the v cc cc pin (8 msbs of reading) these v oltage readings are plement for extended resolution eadings are shou ld be read nce the extended re sters are rea he ex tended 43. temperature reading registers (power-on default = 0x80) egister address r/w description in twos com mat. if the bits of these r also being read, the extended resolution registers (reg. 0x76, 0x77) first. o solution regi d, the associated msb reading registers are frozen until read. both t resolution registers and the msb registers are frozen. table r 0 x25 read-only remote 1 temperature reading 1 (8 msbs of reading) 0x26 read-only local temperature reading (8 msbs of reading) 0x27 read-only remote 2 temperatur e readin g (8 msbs of reading) these v oltage readings are plement form ading of 0x80 in eading register nded resolution bits of these readings eing read, the extend gisters (reg. 0x ters are read, all associated msb in twos com at. 1 note that a re are also b a temperature r ed resolution re indicates a diode fault (open or short) on that channel. if the exte 76, 0x77) should be read first. once the extended resolution reg is reading registers are frozen until read. both the extended resolution registers and the msb registers are frozen.
adt7460 rev. c | page 36 of 52 ist ess r/w description table 44. fan tachometer reading registers (power-on default = 0x00) reg er addr 0x28 read - only tach1 low byte 0x29 read- only tach1 high byte 0x2a read- only tach2 low byte 0x2b rea d- only tach2 high byte 0x2c read-only tach3 low byte 0x2d read - only tach3 high byte 0x2e read- only tach4 low byte 0x2f read- only tach4 high byte the fan tachometer reading re r of 11.11 s periods (based on an internal 90 khz clock) that occur betwee n a e nsecu h the number of tach pulses use an speed to be accurately measured both the low and high bytes are eme to a count of 0xffff indicates tha 1. stalled or blocked (object j a (interna e 3. not populated (the adt7 minimum high and low byt be set to 0xffff.) 4. alternate function , for exa gisters count the numbe numb r of co tive fan tac pulses (default = 2). d to count can be changed using the fan pulses per revolution register (reg. 0x7b). this allows th e f . since a valid fan tachometer reading requires that two bytes are read, the low byte must be re ad first. then frozen until read. at powe r-on, these registers contain 0x0000 until such time as the firs t valid fan tach measur nt is read in these registers. this prevents false interrupts from occurring while the fans are spinning up. t a fan is amming the fan) stroyed) 2. f iled l circuitry d 460 expects to see a fan connected to each tach. if a fan is not connected to that tach, its tach e should mple, tach4 reconfigured as therm pin 5. 2 - e instea urrent c register address r/w wir d of 3-wire f an table 45. c pwm duty ycle registers (power-on default = 0xff) description 0x30 read/ write pwm1 current duty cycle (0% to 100% duty cycle = 0x00 to 0xff) 0x31 read/ to 100% duty cycle = 0x00 to 0xff) write pwm2 current duty cycle (0% 0x32 read/write pwm3 current duty cycle (0% to 100% duty cycle = 0x00 to 0xff) these r egisters reflect the pwm duty cycle driving each fan at any given time. when in automatic fan speed control mode, the ad t7460 reports the pwm duty cycles back through these registers. the pwm duty cycle values vary according to temperature in automatic fan speed control mode. during fan startup, these registers report back 0x00. in software mode, the pwm duty cycle outputs can be s et to any duty cycle value by writing to these registers. table 46. operating point registers (power-on default = 0x64) register address r/w description 0x33 read/write remote 1 operating point register (default = 100c) 0x34 read/write local temp operatin g point register (default = 100c) 0x35 read/write remote 2 operating point register (default = 100c) these registers become read-only when the configuration register 1 lock bit is set to 1. any subsequent attempts to write to th ese registers will fail. these registers set the target operating point for each temperature channel when the dynamic t min control feature is enabled. the fans being controlled are adjusted to maintain temperature about an operating point.
adt7460 rev. c | page 37 of 52 na r/ desc table 47. register 0x36dynamic t min control register 1 (power-on default = 0x00) bit me w ription <0> cy re sb (reg. cont that need to be found to optimize the re sponse of fans and the control loop. r2 ad/write m of 3-bit remote 2 cycle value. the other two bits of the code reside in dynamic t min control register 2 0x37). these three bits define the delay time between making subsequent t min adjustments in the rol loop, in terms of number of monitoring cycl es. the system has associat ed thermal time constants <1> reserved read-only rese r future us rved fo e. < 2> ph read/write phtr copies the t temperatu ote 1 operating point register if therm tr1 1 = 1 remote 1 curren r e to the rem is asserted. the operatin ns the tempe therm g point contai rature at which is asserted. this allows the syste run as quiet i thout affecting system performance. phtr1 = 0 ignores any m to ly as possible w therm assertio ns on the t herm pin. the r emote 1 operating point register reflects its programmed value . <3> phtl read/write phtl opies the lo nt tempe operating point register if therm = 1 c cal channels curre r ature to the local is asserted. the operating point co erature at which m ntains the temp ther is asserted. this allows the syste run as quiet out affect nce. phtl = 0 ignores any m to ly as possible wi th ing system perform a therm assertions on the th erm pin. the local te mperature operating point register eflec r ts its programmed value. <4> phtr2 read/write phtr 2 = 1 copies the remote 2 current temperatur e to the remote 2 operating point register if therm is ted. the operating point contains the temperature at which asser therm is asserted. this allows the em performan system to run as quietly as pos . phtr2 = 0 ignores any sible without syst ce being affected therm assertion s on the t herm pin. the re mote 2 operating point register reflects its programmed value . <5> r1t read/write r1t = 1 enables dynam l on the remo re channel. the chosen t min value is dynamically adjusted based on the current tempe g point, and high and low limits for this zone r1t = dyna the t min val djusted, and the channel behaves as desc in the auto section. ic t min contro te 1 temp eratu ratur e, operatin . 0 disables mic t min control. ue chosen is not a ribed mati c fan control <6> lt read/write lt = 1 enables dynam he local temperature channel. the chosen t min value is dynamically adjusted based on the current tempe int, and high and low limits for this zone = desc ic t min control on t ratur e, operating p o . lt 0 disables dynamic t min control. the t min value chosen is not adjusted, and the channel behaves as ribed in the automati c fan control section. <7> r2t read/write r2t = dyna zone r2t = dyna he t min val adjusted, and the channel behaves as desc in the auto l section. 1 enables dynamic t min control on the remote 2 temp erature channel. the chosen t min value is mically adjusted based on the current temperatur e, operating point, and high and low limits for this . 0 disables mic t min control. t ue chosen is not ribed mati c fan contro this r egist r become read-only when onfigurati ock bit is set t empts to write to this regis ter have no fect. e s the c on register 1 l o 1. further att ef
adt7460 rev. c | page 38 of 52 0x00) e /w iption table 48. register 0x37dynamic t min control register 2 (power-on default = bit nam r descr <2:0> r1 r quent t min of cy read/w ite 3-bit remote 1 cycle value. these three bits defi ne the delay time between making subse adjustments in the control loop for the remote 1 ch annel, in terms of number of monitoring cycles. the system has associated thermal time constants that need to be found to optimize the response fans and the control loop. bits decrease cycle increase cycle 000 4 cycles (0.5 s) 8 cycles (1 s) 001 8 cycles (1 s) 16 cycles (2 s) 010 16 cycles (2 s) 32 cycles (4 s) 011 32 cycles (4 s) 64 cycles (8 s) 100 64 cycles (8 s) 128 cycles (16 s) 101 128 cycles (16 s) 256 cycles (32 s) 110 256 cycles (32 s) 512 cycles (64 s) 512 cycles (64 s) 1024 cycles (128 s) 111 <5:3> r ocal temperature channel, in terms of number stants that need to be found to cyl read/w ite 3-bit local temperature cycle value. these thre e bits define the delay time between making subsequent t min adjustments in the control loop for l of monitoring cycles. the system has associated th ermal time con optimize the response of fans and the control loop. bits decrease cycle increase cycle 000 4 cycles (0.5 s) 8 cycles (1 s) 001 8 cycles (1 s) 16 cycles (2 s) 010 16 cycles (2 s) 32 cycles (4 s) 011 32 cycles (4 s) 64 cycles (8 s) 100 64 cycles (8 s) 128 cycles (16 s) 101 128 cycles (16 s) 256 cycles (32 s) 512 cycles (64 s) 110 256 cycles (32 s) 111 512 cycles (64 s) 1024 cycles (128 s) <7:6> yr2 ri ine the delay time between making subsequent t min e control loop for the remote 2 ch annel, in terms of number of monitoring cycles. of c read/w te 2 lsbs of 3-bit remote 2 cycle value. the msb of the 3-bit code resides in dynamic tmin control register 1 (reg. 0x36). these three bits def adjustments in th the system has associated thermal time constants that need to be found to optimize the response fans and the control loop. bits decrease cycle increase cycle cles (1 s) 000 4 cycles (0.5 s) 8 cy 001 8 cycles (1 s) 16 cycles (2 s) 010 16 cycles (2 s) 32 cycles (4 s) 011 32 cycles (4 s) 64 cycles (8 s) 100 64 cycles (8 s) 128 cycles (16 s) (32 s) 101 128 cycles (16 s) 256 cycles 110 256 cycles (32 s) 512 cycles (64 s) 111 512 cycles (64 s) 1024 cycles (128 s) this register becomes read-only when the configuration register 1 lock bit is set to 1. further attempts to write to this regis ter have no effect.
adt7460 rev. c | page 39 of 52 description table 49. register 0x40configuration register 1 (power-on default = 0x00) bit name r/w <0> strt read/write l g and pwm control outp uts based on the limit settings programmed. l l it an d the default settings are enabled. this bi r ogic 1 enables monitorin ogic 0 disables monitoring and pwm control based on the default power-up limit settings. note that the imit values programmed are preserved even if a logic 0 is written to this b t becomes read-only and cannot be changed once bit 1 (lock bit) has been written. all limit egisters should be programmed by bios before setting this bit to 1. (lockable.) <1> lock write logic 1 locks all o rogue programs such as viruses from modifyin g critical system limit settings. (lockable.) once limit values to their current settings. on ce this bit is set, all lockable registers become read- nly and cannot be modified until the adt7460 is powered down and powered up again. this prevents <2> rdy read-only t ms m his bit is set to 1 by the adt7460 to indicate that the device is fully powered-up and ready to begin syste onitoring. <3> fspd read/write w hen set to 1, all fans run at full speed. power-on default = 0. (this bit cannot be locked.) <4> res read-only reserved for future use. <5> fspdis read l pin- u /write ogic 1 disables fan spin-up for two tach pulses. instea d, the pwm outputs go high for the entire fan s p timeout selected. <6> todi s w 0 to be used with smbus c read/write hen set to 1, the smbus timeout feature is disabl ed. this allows the adt746 ontrollers that cannot handle smbus timeouts. (lockable.) < 7> v cc read/write when set to 1, the adt7460 rescales its v cc pin to measure a 5 v supply. when set to 0, the adt7460 measures v cc as a 3.3 v supply. (lockable.) table 50. register 0x41interrupt ter 1 (power-o name r/w descr status regis n default = 0x00) bit iption <0> 2.5v read-only a 1 ind e 2.5 v high o exceeded. this bit is cleare d on a read of the status register only if the erro r condition icates that th r low limit has been has subsided. <1> res read-only reserved for future use. <2> v cc read-only a 1 indicates that the v cc high or low limit has been exceeded register only if the erro r condition has subsided. . this bit is cleared on a read of the status <3> res read-only reserved for future use. < 4> r1t read-only a 1 indicates that the remote 1 low or high temperatur e limit has been exceeded. this bit is cleared on a read of the status register only if the error condition has subsided. < 5> lt read-only a 1 indicates the local low or high temperature limit has been exceeded. this bit is cleared on a read of the only if the error condition has subsided. status register <6> r2t read-only a 1 indicat esthat the remote 2 low or high temperatur e limit has been exceeded. this bit is cleared on a re the status registe or condition has subsided. ad of r only if the err <7> ool read-only a hat an out- status register 2. this bit is a logical or of all s tatus regis olat ion to determine whether any of the voltage, temperature, or d by status register 2 are out-of-limit. this saves the need to read status regis cycle. 1 indicates t of-limit event has been latched in tatus bits in s ter 2. software can test this bit in is fan speed readings represente ter 2 every interrupt or polling
adt7460 rev. c | page 40 of 52 t = 0x00) w description table 51. register 0x42interrupt status register 2 (power-on defaul bit name r/ <0> res read-only reserved for future use. <1> ovt read-only a 1 indicates that one of the therm overte ceeded. this bit is cleared on a read o gister when the temperatur mperature limits has been ex f the status re e drops below therm ? t hyst . <2> fan1 read-only a at fan 1 has dropped below . this bit is not set when the pw 1 indicates th minimum speed or has stalled m1 output is off. <3> fan2 read-only a at fan 2 has dropped below . this bit is not set when the pw 1 indicates th minimum speed or has stalled m2 output is off. <4> fan3 read-only a at fan 3 has dropped below . this bit is not set when the pwm3 outpu is off. 1 indicates th t minimum speed or has stalled <5> f4p read-only a 1 indicates that fan 4 has dropped below minimum speed or has stalled. this bit is not set when the pwm3 output is off. read-only if pin 9 is configured as the therm timer input for therm monitoring, this bit is set when the therm assertion time exceeds the limit programmed in the therm limit register (reg. 0x7a). < 6> d1 read-only a 1 indicates either an open or short circuit on the thermal diode 1 inputs. <7> d2 read-only a 1 indicates either an open or short circu it on the thermal diode 2 inputs. table 52. voltage limit register s register address r/w description power-on default 0x44 read/write 2.5 v low limit 0x00 0x45 read/write 2.5 v high limit 0xff 0x48 read/write v cc low limit 0x00 0x49 read/write v cc high limit 0xff setting the configuration register 1 lock bit ha high limits: an interrupt is generated when a s no effect on these registers. value exceeds its high limit (> comparison). limi te is gener lue is equal to or below its low limit ( comparison). perature limit re ss r description power-on default low ts: an in rrupt ated when a va table 53. tem gister s register addre /w 0x 4e r e te 1 temperature low limit 0x81 ead/w rit remo 0x 4f r e remote 1 temperature high limit 0x7f ead/w rit 0x50 r e local temperature low limit 0x81 ead/w rit 0x51 r e local temperature high limit 0x7f ead/w rit 0x52 r e remote 2 temperature low limit 0x81 ead/w rit 0x 53 r e remote 2 temperature high limit 0x7f ead/w rit excee din th ur egister. setting the igura regi high limits: an interrupt is gene mi te r g any of ese temperat e limits by 1c causes the appropriate status bit to be set in the interrupt status r conf tion ster 1 lock bit has no effect on these registers. rated when a value exceeds its high limit (> comparison). low li ts: an in rrupt is gene ated when a value is equal to or below its low limit ( comparison).
adt7460 rev. c | page 41 of 52 r/w table 54. fan tachometer limit registers (power-on default = 0xff) register address description 0x54 read/ write tach1 minimum low byte 0x55 read/ write tach1 minimum high byte 0x56 read/ write tach2 minimum low byte 0x57 read/write tach2 minimum high byte 0x58 read/write tach3 minimum low byte 0x59 read/write tach3 minimum high byte 0 x5a read/write tach4 minimum low byte 0x5b read/write tach4 minimum high byte exce eding he limit registe tes that the fan is running too slowly or has stalled. the approp ate sta tu it is set rup s r dicate register 1 lock bit has no effect on es e regis 55. pwm configuration registe o r- ult = 0x62) ess r/w on any of t tach rs by 1 indica ri s b in inter t statu egister 2 to in the fan failure. setting the configuration th ters. table rs (p we on defa registeraddr descripti 0x5c read/ pwm1 configuration write 0x5d read/ write pwm2 configuration 0x5e read/ write pwm3 configuration these registers become read-only when registers will fail. 56. pwm con iguration registe name description the configuration register 1 lock bit is set to 1. any subsequent attempts to write to th ese table f r bits bit r/w <2:0> spin read /write these bits control the start-up t imeout for pwmx. the pwm output stays high until two valid tach rising edges e om the fan. if there is not a valid tach signal during the fan tach measurement directly after the fan start-up timeout period, the tach meas urement reads 0xffff and status register 2 reflects the fan fault. if the tach minimum high and low byte contains 0xffff or 0x0000, the status register 2 bit is not set, even if the fan has not started. are se n fr 000 s t- eout = no tar up tim 001 0 = 10 ms 010 0 ( t) = 25 ms defaul 011 0 = 40 ms 100 7 = 66 ms 101 = 1 s 110 = 2 s 111 = 4 s <3> slow /write slow a tes for acoustic enhancement four times longer. read = 1 m kes the ramp ra < 4> inv read/write this bit inverts the pwm o utput. the default is 0, wh ich corresponds to a logic high output for 100% duty cycle. setting this bit to 1 inverts the pwm output, so 100% duty cycle corresponds to a logic low output. <7:5> bhvr read/write these bits assign each fan to a particular temperature sens or for localized cooling. 000 = remote 1 temperature controls pwmx (automatic fan control mode). 001 = local temperature controls pwmx (automatic fan control mode). 010 = remote 2 temperature controls pwmx (automatic fan control mode). 011 = pwmx runs full speed (default). 100 = pwmx is disabled. 101 = fastest speed calculated by loca l and remote 2 temperature control pwmx. 110 = fastest speed calculated by a ll three temperature channels control pwmx. 111 = manual mode. pwm duty cycle regi sters (reg. 0x30C0x32) become writable.
adt7460 rev. c | page 42 of 52 iste s description table 57. temp t range /pwm frequency registers (power-on default 0xc4) reg r addre s r/w 0x5f read/write remote 1 t range /pwm1 frequency 0x60 read/write local temp t range /pwm2 frequency 0x61 read/write remote 2 t /pwm3 frequency range th ese re isters b es read-o h t onfiguration regis ock bit is set to 1. further attempts to write to this reg ister have no fect. p range /pwm u y gister bits r/w g ecom nly w en he c ter 1 l ef table 58. tem t freq enc re bit name description <2:0> freq read/writ h bits control the pw quency. e t ese mx fre = 11.0 hz 000 001 = 14.7 hz 010 = 22.1 hz 011 = 29.4 hz 100 = 35.3 hz (default) 101 = 44.1 hz 110 = 58.8 hz 111 = 88.2 hz <3> t hrm read/write thrm = 1 causes the therm pin (pin 9) to assert low as an output when this temperature channels therm limit is exceeded by 0.25c. the therm pin re mains asserted until the temperature is equal to or below the therm limit. the minimum time that therm asserts for is one monitoring cycle. this allows clock modulation of devices that incorporate this feature. thrm = 0 makes the therm pin act as an input only, for example, for pentium 4 prochot therm monitoring, when pin 9 is configured as . <7:4> rang read/writ ature slope for automatic fan control e e these bits determine the pwm duty cycle vs. temper . 0000 = 2c 0001 = 2.5c 0010 = 3.33c 0011 = 4c 0100 = 5c 0101 = 6.67c 0110 = 8c 0111 = 10c 1000 = 13.33c 1001 = 16c 1010 = 20c 1011 = 26.67c 1100 = 32c (default) 1101 = 40c 1110 = 53.33c 1111 = 80c
adt7460 rev. c | page 43 of 52 r d table 59. register 0x62enhance acoustic s register 1 (power-on default = 0x00) bit name /w escription <2:0> acou r t i e ead/write hese bits select the ramp rate a pplied to the pwm1 output. instead of pwm1 jumping instantaneously to ts newly calculated speed, pwm1 ramps gracefully at the rate determined by these bits. this feature nhances the acoustics of the fan being driven by the pwm1 output. t t ime slot increase ime for 33% to 100% 000 = 1 35 s 001 = 2 17.6 s 010 = 3 18 s 011 = 5 7 s 100 = 8 4.4 s 101 = 12 3 s 110 = 24 1.6 s 111 = 48 0.8 s <3> en1 r w ead/write hen this bit is 1, acou stic enhancement is en abled on pwm1 output. <4> sync r s t s ead/write ync = 1 synchronizes fan speed measurements on ta ch2, tach3, and tach4 to pwm3. this allows up to hree fans to be driven from pwm3 o utput and their speeds to be measured. ync = 0, only tach3 and tach4 are synchronized to pwm3 output. <5> m in1 read/write w in automatic defines wh ether pwm1 is off (0% duty cycle) or at pwm1 minimum duty cycle when the controlling temperature is below its t min ? hysteresis value. hen the adt7460 is fa n control mode, this bit 0 % ty cycle below t min ? hysteresis = 0 du 1 w minimum duty cycle below t min ? hysteresis = p m1 <6> m in2 read/write when the adt7460 is in automatic fan speed control mo de, this bit defines whethe r pwm2 is off (0% duty cycle) or at pwm2 minimum duty cycle when the controlling temperature is below its t min ? hysteresis value. 0 min ? hysteresis = 0% duty cycle below t 1 m duty cycle below t min ? hysteresis = pwm2 minimu <7> m in3 read when the adt7 he r pwm3 is off (0% duty c e is below its t min ? hysteresis /write 460 is in automatic fan speed control mo de, this bit defines whet ycle) or at pwm3 minimum duty cycle when the controlling temperatur value. 0 = 0% duty cycle below t min ? hysteresis 1 = pwm3 minimum duty cycle below t min ? hysteresis t his register becomes read-only when the configuration register 1 lock bit is set to 1. further attempts to write to this regis ter have no ffect. e
adt7460 rev. c | page 44 of 52 enhance acoustic s register 2 (power-on default = 0x00) description table 60. register 0x63 bit name r/w <2:0> acou3 read/write th ct the ramp r put. instead of g instantaneously to its lated speed, the rate determin its. this effect en coustics of t pwm3 output. ese bits sele ate a pplied to the pwm3 out pwm3 jumpin newly calcu pwm3 ramps gracefully at ed by these b hances the a he fan being driven by the time slot increase time for 33% to 100% 000 = 1 35 s 001 = 2 17.6 s 010 = 3 11.8 s 011 = 5 7 s 100 = 8 4.4 s 101 = 12 3 s 110 = 24 1.6 s 111 = 48 0.8 s <3> en3 read/ write when this bit is 1, acou stic is en abled on pwm3 outpu enhancement t. <6:4> acou2 read/write t ct the ramp 2 output. instead ing instantaneously to it ted speed fully at the rate determ bits. this effect e acoustics of the pwm2 outpu hese bits sele rate a pplied to the pwm of pwm2 jump s newly calcula , pwm2 ramps grace ined by these nhances the the fans being driven by t. time slot increase time for 33% to 100% 000 = 1 35 s 001 = 2 17.6 s 010 = 3 11.8 s 011 = 5 7 s 100 = 8 4.4 s 101 = 12 3 s 110 = 24 1.6 s 111 = 48 0.8 s <7> en2 read/write when this bit is 1, acou stic enhancement is en abled on pwm2 output. this register becomes read-only when the con figuration register 1 lock bit is set to 1. further attempts to write to this regis ter have no effect. table 61. pwm min duty cycle registers register address r/w description power-on default 0x64 read/write pwm1 min duty cycle 0x80 (50% duty cycle) 0x65 read/write pwm2 min duty cycle 0x80 (50% duty cycle) 0x66 read/write pwm3 min duty cycle 0x80 (50% duty cycle) these registers become read-o nly when the adt7460 is in automatic fan control mode. read/wr ion table 62. pwm min duty cycle register bits bit name ite descript <7:0> pwm duty cy /wri e pwm min duty cycle for pwmx. cle read te these bits define th 0x00 cyc = 0% duty le (fan off) 0x40 % duty cy = 25 cle 0x80 = 50% duty cy cle ff 00% duty c 0x = 1 ycle (fan full speed)
adt7460 rev. c | page 45 of 52 r/w description power-on default table 63. t min registers register address 0x67 read emperature t min 0x5a (90c) /write remote 1 t 0x68 read /write local temperature t min 0x5a (90c) 0x69 read /write remote 2 temperature t min 0x5a (90c) these are the t registers for each temperature channel. when the temperature measured exceeds t , the appropriate fan runs at egisters become read-only when the configuration register 1 lock bit is set. further attempts to write to these register s have no ffect. min min minimum speed and increase with temperature according to t range . these r e table 64. therm limit registers regis ter address r/w tion power-on default descrip 0x6a read/write remote 1 therm limit 0x64 (100c) 0x6b r ead /write local therm limit 0x64 (100c) 0x6c read/write remote 2 therm limit 0x64 (100c) if any te mperature measured exceeds its therm limit, all pwm outputs drive their fans at 100% duty cycle. this is a fail-safe mechanism rporated to cool the system in the event of a critical overtemperature. it also ensures some level of cooling in the event that software r hardware locks up. if set to 0x80, this feature is disabled. the pwm output remains at 100% until the temperature drops belo w herm inco o t limit C hysteresis. if the therm pin is programmed as an output, exceeding these limits by 0.25c can cause the therm pin et to 1. further attempts to write to these reg isters have table 65. temperature hysteresis registers to assert low as an output. these registers become rea -only when the configuration register 1 lock bit is s d no effect. register address r/w description power-on default 0x6d read/write remote 1 loca l temperature hysteresis 0x44 0 x6e read/write remote 2 temperature hysteresis 0x40 each 4-bit value controls the amount of temperature hysteresis applied to a particular temperature channel. once the temperatur e for that channel falls below its t min value, the fan remains running at pwm min duty cycle until the temperature = t min C hysteresis. up to 15c of hysteresis may be assigned to any temperature channel. the hysteresis value chosen also applies to that temperature channel if its therm limit is exceeded. the pwm output being controlled goes to 100% if the therm limit is exceeded and remains at 100% until the temperature drops below therm C hysteresis. for acoustic reasons, it is recommended that the hysteresis value not be programmed less than 4c. setting the hysteresis value lower than 4c causes the fan to switch on and off regularly when the temperature is clo se to t min. these registers become read-only when the configuration register 1 lock bit is set to 1. further attempts to write to these reg isters have no effect. table 66. xnor tree test enable register (power-on default = 0x00) register address r/w description 0x6f read/write xnor tree test enable bit mnmeonic description <0> xen if the xen bit is set to 1, the devi ce enters the xnor tree test mode. clearing the bit removes the devi ce from the xnor test mode. <7:1> res unused. do not write to these bits. this register becomes read-only when the configuration register 1 lock bit is set to 1. further attempts to write to this regis ter have no effect.
adt7460 rev. c | page 46 of 52 is re r/w iption table 67. remote 1 temperature offset register (power-on default = 0x00) reg ter add ss descr 0x7 0 rit read/w e remote 1 temperature offset <7:0> read/writ e stem offsets such as pcb e allows a twos complement offset value to be automatically adde d to or subtracted from th remote 1 temperature reading. this is to compensate for any inhere nt sy trace resistance. lsb value = 0.25c. this register becomes read-only ve no ct table 68. local temperature o gis dre when the configuration register 1 lock bit is set to 1. further attempts to write to this regis ter ha effe . ffset register (power-on default = 0x00) re ter ad ss r/w description 0x71 read/wri te local temperature offset <7 :0> wri al read/ te allows a twos complement offset value to be automatically added to or subtracted from the loc temperature reading. lsb value = 0.25c. this register becomes read-only effect. able remo 2 temperature offset register (power-on d x00) r/w description when the configuration register 1 lock bit is set to 1. further attempts to write to this regis ter have no t 69. te efault = 0 register addre ss 0x72 read/writ remote 2 temperature e offset <7:0> read /write allows a twos complem be automatically adde d to or subtracted from the ent offset value to remote 2 temperature reading. this is to compensate for any inhere nt system offsets such as pcb trace resistance. lsb value = 0.25c. this register becomes read-only w n register 1 lock bit is set to 1. further attempts to write to this regis ter have no hen the configuratio effect.
adt7460 rev. c | page 47 of 52 na r/ d table 70. register 0x73configuration register 2 (power-on default = 0x00) bit me w escription 0 ain re ai ns measured using th e tach output from the fan. ain1 = 1, pin 6 is re al sensing resistor and coupling ca configuration register 4 (reg. 0x7d). 1 ad/write n1 = 0, speed of 3-wire fa configured to measure the speed of 2-wire fans using an extern pacitor. ain voltage threshold is set vi a 1 ain2 read/write ain2 = 0, speed e tach output from the fan. ain2 = 1, pin 7 is re ire fans using an external sensing resistor and coupling ca configuration register 4 (reg. 0x7d). of 3-wire fans measured using th configured to measure the speed of 2-w pacitor. ain voltage threshold is set vi a 2 ain read/write ai re -wire fans using an external sensing resistor and coupling ca x7d). 3 n3 = 0, speed of 3-wire fans measured using th e tach output from the fan. ain3 = 1, pin 4 is configured to measure the speed of 2 pacitor. ain voltage threshold is set vi a configuration register 4 (reg. 0 3 ain read/write ai fan. ain4 = 1, pin 9 is reconfigured to measure the sp sistor and coupling capacitor. ain voltage threshold is set vi a configuration register 4 (reg. 0x7d). 4 n4 = 0, speed of 3-wire fans measured using th e tach output from the eed of 2-wire fans using an external sensing re 4 avg read/write avg = 1, averaging on the temperature and volt age measurements is turned off. this allows measurements on each channe l to be made much faster. 5 attn read/write attn = 1, the adt7460 remo functions such as connecting up external se ves the attenuators from the 2.5 v input. the input can be used for other nsors. 6 conv read/write conv = 1, the a sion mode. in this mode, the adt7460 can be remote 1 temperature. it is also possible to start adc conversions using an external clock on pin 6 by setting bit 2 of test register 2 (reg. 0x7f). this m terize/pro file cpu temperature quickly. the ap selected by writing to bits <7:5> of tach1 min high byte register (reg. 0x55). dt7460 is put into a single-channel adc conver made to read continuously from one input only, for example, ode could be useful if, for exampl e, users wanted to charac propriate adc channel is bits <7:5> reg. 0x55 channel selected 000 2.5 v 010 v cc (3.3 v) 101 remote 1 temp 110 local temp 111 remote 2 temp 7 sh read/write sh 460 goes into shutdown mode. all pwm outputs assert low (or high depending, on state of inv bit) he pwm current duty cycle registers read 0x00 to indicate that the fans ar dn dn = 1, adt7 to switch off all fans. t e not being driven. this re gi m ly w ter have no able 71. register 0x74interrupt mask register 1 (power-on default <7:0> = 0x00) ster beco es read-on hen the configuration register 1 lock bit is set to 1. further attempts to write to this regis effect. t bit name r/w description 0 2.5v read/write a 1 masks smbalert for out-of-limit conditions on the 2.5 v channel. 1 res read/write reserved for future use. 2 v cc rea a d/write 1 masks smbalert for out-of-limit conditions on the v cc channel. 3 r rea r es d/write eserved for future use. 4 r a 1t read/write 1 masks smbalert for out-of-limit conditions on th e remote 1 temperature channel. 5 lt read/write a 1 masks smbalert for out-of-limit conditions on the local temperature channe l. 6 r read/write a 2t 1 masks smbalert for out-of-limit conditions on th e remote 2 temperature channel. 7 o read/write a ol 1 masks smbalert for any out-of-limit conditio n in status register 2.
adt7460 rev. c | page 48 of 52 ) r/w description table 72. register 0x75interrupt mask register 2 (power-on default = 0x00 bit name 0 res read/write reserved for future use. 1 ovt read-only a 1 masks smbalert for overtemperature therm conditions. 2 fan1 read/write a 1 masks smbalert for a fan 1 fault. 3 fan2 read/write a 1 masks smbalert for a fan 2 fault. 4 fan3 read/write a 1 masks smbalert for a fan 3 fault. 5 f4p read/write a 1 masks smbalert for a fan 4 fault. if the ta ch4 pin is being used as the therm input, this bit masks smbalert for a therm timer event. 6 d1 read/write a 1 masks smbalert for a diode open or short on remote 1 channel. 7 d2 read/write a 1 masks smbalert for a diode open or short on remote 2 channel. table 73. register 0x76extended resolution register 1 bit name r/w description < 1:0> 2.5v read-only 2.5 v lsbs. holds the 2 lsbs of the 10-bit 2.5 v measurement. < 3:2> res read/write reserved for future use. < 5:4> v cc read-only v cc lsbs. holds the 2 lsbs of the 10-bit v cc measurement. <7:6> res read/write reserved for future use. if th is re read, t gister and holding the msb of each reading are frozen unti ead. 0x77extended resolution 2 r/w description gister is his re the registers l r table 74. register register bit name <1:0> read/write reserved for future use. res <3:2> tdm1 rea re d-only mote 1 tempera ture lsbs. holds the 2 lsbs of the 10-bi t remote 1 temperature measurement. <5:4> ltmp read-only lo 10-bit local temperature measurement. cal temperature lsbs. holds the 2 lsbs of the <7:6> t dm2 rea -only remote 2 tempera ture lsbs. holds the 2 lsbs of the 10-bi t remote 2 temperature measurement. d i f this re ister is read, t is register and isters holding the msb of each reading are frozen until read. table 75. register 0x78configura r/w de g h the reg tion register 3 (power-on default = 0x00) bit name scription <0> alert read/write alert = 1, pin 5 (pwm2/ smbalert ) is configured as an smbalert interrupt output to indicate out-of- lim s. it error condition <1> therm nable read/write th e erm en able = 1 enables therm monitoring functionality on pi n 9 when it is configured as therm . w rm hen the is asserted, fans can be ru n at full speed (if the boost bit is set), or a timer can be tri ggered to time how long therm has been asserted for. <2> boost read/write bo ost = 1, assertion of therm causes all fans to run at 100% duty cycle for fail-safe cooling. <3> ast read/write fa t tach measurements on all channels. this increases the tach measurement rate from once per second, to once every 250 ms (4). f st = 1 enables fas <4> d c1 read/write dc1 = 1 enables tach measur ements to be continuo usly made on tach1. <5> d c2 read/write dc2 = 2 enables tach measur ements to be continuo usly made on tach2. <6> d c3 read/write dc3 = 1 enables tach measur ements to be continuo usly made on tach3. < 7> dc4 read/write dc4 = 1 enables tach measur ements to be continuo usly made on tach4. this r e egister becomes read-only when the configuration register 1 lock bit is set to 1. further attempts to write to this regis ter have no ffect.
adt7460 rev. c | page 49 of 52 table 76. register 0x79 therm status register (power-on default = 0x00) bit /w tion name r descrip <7:1> ly times how long therm tmr read-on input is asserted. these s even bits read 0 until the therm assertion time exceeds 45.52 ms. <0> asrt/tmr0 read-only is set high on the assertion of the therm input. cleared on read. if the therm assertion time exceeds set and becomes the ls b of the 8-bit tmr reading. this allows therm 45.52 ms, this bit is assertion 6 ms. times from 45.52 ms to 5.82 s to be repor ted back with a reso lution of 22.7 t able 7 giste 0x7a the 7. re r rm limit regi ster (pow description er-on default = 0x00) bit name r/w <7:0> limt read/write sets maximum therm assertion length allowed before an interru pt is generated. this is an 8-bit limi t with a resolution of 22.76 ms allowing therm assertion limits of 45.52 ms to 5.82 s to be programmed. if the therm assertion time exceeds this limit, bit 5 (f4p) of interrupt status register 2 (reg. 0x42) is set. if the limit value is 0x00, an interrupt is generated immediately upon the assertion of the therm input. an r/w description table 78. register 0x7bf pulses per revo lution register (power-on default = 0x55) bit name < 1:0> fan1 read/write sets number of pulses to be coun ted when measuring fan1 speed. can be used to determine fans pulses per revolution for unknown fan type. pulses counted 00 = 1 01 = 2 (d efault) 10 = 3 11 = 4 < 3:2> fan2 read/write sets number of pulses to be co unted when measuring fan2 speed. can be used to determine fans pulses per revolution for unknown fan type. pulses counted 00 = 1 01 = 2 (default) 10 = 3 11 = 4 <5:4> fan3 read/write sets number of pulses to be co unted when measuring fan3 speed. can be used to determine fans pulses per revolution for unknown fan type. pulses counted 00 = 1 01 = 2 (default) 10 = 3 11 = 4 <7:6> fan4 read/write sets number of pulses to be co unted when measuring fan4 speed. can be used to determine fans pulses per revolution for unknown fan type. pulses counted 00 = 1 01 = 2 (default) 10 = 3 11 = 4
adt7460 rev. c | page 50 of 52 ation register 4 (power-on default = 0x00) cription table 79. register 0x7dconfigur bit name r/w des < 0> al2.5v read/write al2.5v = 1, pin 14 (2.5v/ smbalert ) is configured as an smbalert interrupt output to indicate out-of-limit error conditions. al2.5v = 0, pin 14 (2.5v/ smbalert ) is configured as a 2. 5 v measurement input. <1> res read-only reserved for future use. <3:2> ainl read/write these two bits define the input threshold for 2-wire fan speed measurements: 00 = 20 mv 01 = 40 mv 10 = 80 mv 11 = 130 mv <7:4> res reserved for future use. this register becomes read-only when the configuration register 1 lock bit is set to 1. further attempts to write to this regis ter have no effect. table 80. register 0x7emanufacturers test register 1 (power on-default = 0x00) bit name read/write description <7:0> res read-only manufacturers test register. these bits are reserved for manufacturers test purposes and should not be written to under normal operation. table 81. register 0x7fmanufact (power-on d read/write des urers te st register 2 efault = 0x00) bit name cription <7:0> res re ad-only manufacturers test register. these bits a anufacturers test pu nd should not be writ al operation. re reserved for m rposes a ten to under norm
adt7460 rev. c | page 51 of 52 outline dimensions 16 9 8 1 pin 1 sea t i n g pl a n e 0 . 010 0 . 004 0. 01 2 0. 00 8 0. 02 5 bs c 0. 0 1 0 0. 0 0 6 0 . 050 0 . 016 8 0 coplanarity 0.004 0. 0 6 5 0. 0 4 9 0. 06 9 0. 05 3 0. 15 4 bs c 0. 2 3 6 bs c compliant to jedec standards mo-137ab 0. 19 3 bs c f i gure 55. 1 6 -l ead shrink sm al l o u t lin e p a ckage [qs o p ] (r q - 16) di me nsio ns sho w n i n mi ll im e t e r s ordering guide model temperature r a nge package descri ption package option adt7460arq ?40c to +120c 16-lead qsop rq-16 adt7460arq-r eel ?40c to +120 c 16-lead qsop rq-16 adt7460arq-r eel7 ?40c to +120 c 16-lead qsop rq-16 adt7460arqz 1 ?40c to +120c 16-lead qsop rq-16 adt7460arqz- reel 1 ?40c to +120c 16-lead qsop rq-16 adt7460arqz- reel7 1 ?40c to +120c 16-lead qsop rq-16 eval-ad t7460e b evaluation boar d 1 z = pb-free part.
adt7460 rev. c | page 52 of 52 notes ? 2005 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. c03228?0?3/05(c)

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