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general description the MAX6640 monitors its own temperature and one external diode-connected transistor or the temperatures of two external diode-connected transistors, typically available in cpus, fpgas, or gpus. the 2-wire serial interface accepts standard system management bus (smbus) tm write byte, read byte, send byte, and receive byte commands to read the temperature data and program the alarm thresholds. temperature data can be read at any time over the smbus, and three pro- grammable alarm outputs can be used to generate interrupts, throttle signals, or overtemperature shut- down signals. the temperature data is also used by the internal dual pwm fan-speed controller to adjust the speed of up to two cooling fans, thereby minimizing noise when the system is running cool, but providing maximum cooling when power dissipation increases. speed control is accomplished by tachometer feedback from the fan, so that the speed of the fan is controlled, not just the pwm duty cycle. accuracy of speed measurement is 4%. the MAX6640 is available in 16-pin qsop and 16-pin tqfn 5mm x 5mm packages. it operates from 3.0v to 5.5v and consumes just 500? of supply current. applications desktop computers notebook computers workstations servers networking equipment features ? two thermal-diode inputs ? local temperature sensor ? 1? remote temperature accuracy (+60? to +100?) ? two pwm outputs for fan drive (open drain; can be pulled up to +13.5v) ? programmable fan-control characteristics ? automatic fan spin-up ensures fan start ? controlled rate-of-change ensures unobtrusive fan-speed adjustments ? ?% fan-speed measurement accuracy ? temperature monitoring begins at por for fail- safe system protection ? ot and therm outputs for throttling or shutdown ? measures temperatures up to +150? ? tiny 5mm x 5mm 16-pin tqfn and qsop packages MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller ________________________________________________________________ maxim integrated products 1 ordering information 19-3344; rev 0; 8/04 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. part operating range measurement range pin- package MAX6640aee -40 c to +125 c 0? to +150? 16 qsop MAX6640ate -40 c to +125 c 0? to +150? 16 tqfn (5mm x 5mm) 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 pwm1 scl sda v cc dxp2 dxn gnd dxp1 top view MAX6640 qsop tach1 pwm2 tach2 v cc fanfail therm ot alert pwm2 1 tach2 2 3 4 fanfail therm 12 v cc 11 10 9 dxp2 dxn 5 v cc 6 7 8 gnd dxp1 ot 16 pwm1 15 14 13 sda scl tach1 alert MAX6640 *connect exposed paddle to gnd 5mm x 5mm thin qfn pin configurations smbus is a trademark of intel corp. typical application circuit appears at end of data sheet.
MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = +3.0v to +5.5v, t a = 0 c to +125 c, unless otherwise noted. typical values are at v cc = +3.3v, t a = +85?.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v cc to gnd ..............................................................-0.3v to +6v pwm1, pwm2, tach1, and tach2 to gnd ......-0.3v to +13.5v dxp1 and dxp2 to gnd ..........................-0.3v to +(v cc + 0.3v) dxn to gnd ..........................................................-0.3v to +0.8v scl, sda, therm , ot , fanfail , and alert to gnd ..............................................-0.3v to +6v sda, ot , therm , alert , fanfail , pwm1, and pwm2 current .............................-1ma to +50ma dxn current .......................................................................?ma esd protection (all pins, human body model) ..................2000v continuous power dissipation (t a = +70?) 16-pin qsop (derated 8.3mw/? above +70?) ....... 667mw 16-pin tqfn 5mm x 5mm (derated at 33.3mw/? above +70?)................2666.7mw operating temperature range .........................-40? to +125? junction temperature ......................................................+150? storage temperature range ............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units operating supply voltage range v cc +3.0 +5.5 v standby current smb static, sleep mode 3 10 a operating current interface inactive, adc active 0.5 1 ma v cc = +3.3v, +60 c t a +100 c and +60 c t r +100 c ? v cc = +3.3v, +40 c t a +100 c and 0 c t r +145 c ?.5 external temperature error v cc = +3.3v, 0 c t r +145 c ?.8 c v cc = +3.3v, +25 c t a +100 c ? internal temperature error v cc = +3.3v, 0 c t a +125 c ? c supply sensitivity of temperature measurement ?.2 ?/v +0.125 c temperature resolution 11 bits conversion time 125 ms conversion-rate timing error -10 +10 % pwm frequency error -10 +10 % tachometer accuracy v cc = 3.135v to 3.345v, +60? t a +85? ? % high level 70 100 130 remote-diode sourcing current low level 7.0 10 13.0 ? dxn source voltage 0.7 v
MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = +3.0v to +5.5v, t a = 0 c to +125 c, unless otherwise noted. typical values are at v cc = +3.3v, t a = +85?.) (note 1) parameter symbol conditions min typ max units digital inputs and outputs alert , fanfail , therm , ot sda i sink = 6ma 0.4 output low voltage (sink current) ( ot , alert , fanfail , therm , sda, pwm1, and pwm2) v ol pwm1, pwm2, i sink = 4ma 0.4 v output high leakage current ( ot , alert , fanfail , therm , sda, pwm1, and pwm2) i oh 1a logic-low input voltage (sda, scl, therm , tach1, tach2) v il 0.8 v v cc = 3.3v 2.1 logic-high input voltage (sda, scl, therm , tach1, tach2) v ih v cc = 5.5v 2.6 v input leakage current (sda, scl, therm , tach1, tach2) v in = v cc or gnd 1 a input capacitance c in 5pf smbus timing (note 2) serial clock frequency f scl (note 3) 10 100 khz clock low period t low 10% to 10% 4 s clock high period t high 90% to 90% 4.7 ? bus free time between stop and start condition t buf 4.7 ? smbus start condition setup time t su:sta 90% of smbclk to 90% of smbdata 4.7 ? start condition hold time t hd:sto 10% of sda to 10% of scl 4 s stop condition setup time t su:sto 90% of scl to 10% of sda 4 s data setup time t su:dat 10% of sda to 10% of scl 250 ns data hold time t hd:dat 10% of scl to 10% of sda (note 4) 300 ns smbus fall time t f 300 ns smbus rise time t r 1000 ns smbus timeout t timeout 58 74 90 ms note 1: all parameters tested at a single temperature. specifications are guaranteed by design. note 2: timing specifications guaranteed by design. note 3: the serial interface resets when scl is low for more than t timeout . note 4: a transition must internally provide at least a hold time to bridge the undefined region (300ns max) of scl's falling edge.
MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller 4 _______________________________________________________________________________________ t ypical operating characteristics (v cc = 3.3v, t a = +25?) standby supply current vs. supply voltage MAX6640 toc01 supply voltage (v) supply current ( a) 5.0 4.5 4.0 3.5 1 2 3 4 5 6 7 8 9 10 0 3.0 5.5 operating supply current vs. supply voltage MAX6640 toc02 supply voltage (v) supply current ( a) 5.0 4.5 4.0 3.5 300 400 500 600 700 800 200 3.0 5.5 remote temperature error vs. remote-diode temperature MAX6640 toc03 temperature ( c) temperature error ( c) 100 75 50 25 -1 0 1 2 -2 0 125 fairchild 2n3906 local temperature error vs. die temperature MAX6640 toc04 temperature ( c) temperature error ( c) 100 75 50 25 -0.5 -1.0 -1.5 0 0.5 1.0 -2.0 0 125 local temperature error vs. power-supply noise frequency MAX6640 toc06 frequency (hz) temperature error ( c) 10k 1k 100 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 -2.0 11 0 100k v in = 250mv p-p square wave applied to v cc with no bypass capacitor remote temperature error vs. common-mode noise frequency MAX6640 toc07 frequency (hz) temperature error ( c) 10k 1k 100 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 -2.0 0.1 1 10 100k v in = ac-coupled to dxp and dxn v in = 100mv p-p square wave remote temperature error vs. differential noise frequency MAX6640 toc08 frequency (hz) temperature error ( c) 10k 1k 100 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 -2.0 10 100k v in = ac-coupled to dxp v in = 100mv p-p square wave temperature error vs. dxp-dxn capacitance MAX6640 toc09 dxp-gnd capacitance (nf) temperature error ( c) 10 1 -5.0 -4.0 -3.0 -2.0 -1.0 0 1.0 2.0 -6.0 0.1 100 remote temperature error vs. power-supply noise frequency MAX6640 toc05 frequency (hz) temperature error ( c) 10k 1k 100 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 -2.0 10 100k v in = 250mv p-p square wave applied to v cc with no bypass capacitor
MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller _______________________________________________________________________________________ 5 pin tqfn qsop name function 1, 15 3, 1 pwm2, pwm1 open-drain output to power transistor driving fan. connect to the gate of a mosfet or base of a bipolar transistor. pwm_ requires a pullup resistor. the pullup resistor can be connected to a supply voltage as high as 13.5v, regardless of the MAX6640? supply voltage. 2, 16 4, 2 tach2, tach1 tachometer inputs. connect to the tachometer output of the fan. tach_ requires a pullup resistor. the pullup resistor can be connected to a supply voltage as high as 13.5v, regardless of the MAX6640? supply voltage. 35 fanfail active-low, open-drain, fan-failure output. open circuit when v cc = 0. 46 therm active-low, open-drain thermal alarm output. typically used for clock throttling. open circuit when v cc = 0. 57 ot active-low, open-drain overtemperature output. typically used for system shutdown or clock throttling. can be pulled up to 5.5v regardless of v cc . open circuit when v cc = 0. 68v cc power-supply input. 3.3v nominal. bypass v cc to gnd with a 0.1? capacitor. 71 0 gnd ground. connect to a clean ground reference. 8, 10 9, 12 dxp1, dxp2 c om b i ned c ur r ent s our ce and a/d p osi ti ve inp ut for rem ote d i od e. c onnect to anod e of r em ote- d i od e- connected tem p er atur e- s ensi ng tr ansi stor . d o not l eave fl oati ng ; c onnect to d x n i f no r em ote d i od e i s used . p l ace a 2200p f cap aci tor b etw een d x p _ and d x n for noi se fi l ter i ng . 91 1 dxn connect cathode of the remote-diode-connected transistor to dxn 11 13 v cc connect to v cc 12 14 alert active-low, open-drain smbus alert output 13 16 scl smbus serial-clock input. can be pulled up to 5.5v regardless of v cc . open circuit when v cc = 0. 14 15 sda smbus serial-data input/output, open drain. can be pulled up to 5.5v regardless of v cc . open circuit when v cc = 0. pin description t ypical operating characteristics (continued) (v cc = 3.3v, t a = +25?) pwmout frequency vs. die temperature MAX6640 toc10 temperature ( c) pwmout frequency (hz) 85 60 35 10 -15 31 32 33 34 35 30 -40 110 pwmout frequency vs. supply voltage MAX6640 toc11 supply voltage (v) pwmout frequency (hz) 5.0 4.5 4.0 3.5 31 32 33 34 35 30 3.0 5.5
MAX6640 detailed description the MAX6640 monitors its own temperature and a remote diode-connected transistor or the temperatures of two external diode-connected transistors, which typi- cally reside on the die of a cpu or other integrated cir- cuit. the 2-wire serial interface accepts standard smbus write byte, read byte, send byte, and receive byte commands to read the temperature data and pro- gram the alarm thresholds. temperature data can be read at any time over the smbus, and a programmable alarm output can be used to generate interrupts, throt- tle signals, or overtemperature shutdown signals. the temperature data is also used by the internal dual pwm fan-speed controller to adjust the speed of up to two cooling fans, thereby minimizing noise when the system is running cool, but providing maximum cooling when power dissipation increases. rpm feedback allows the MAX6640 to control the fan? actual speed. 2-channel temperature monitor with dual automatic pwm fan-speed controller 6 _______________________________________________________________________________________ gnd smbus interface and registers logic pwm generator block v cc temperature processing block sda scl dxp1 dxn pwm1 pwm2 t ach1 t ach2 dxp2 ot therm f anfail alert MAX6640 block diagram write byte format read byte format send byte format receive byte format slave address: equiva- lent to chip-select line of a 3-wire interface command byte: selects which register you are writing to data byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate) slave address: equiva- lent to chip-select line command byte: selects which register you are reading from slave address: repeated due to change in data- flow direction data byte: reads from the register set by the command byte command byte: sends com- mand with no data, usually used for one-shot command data byte: reads data from the register commanded by the last read byte or write byte transmission; also used for smbus alert response return address s = start condition shaded = slave transmission p = stop condition /// = not acknowledged figure 1. smbus protocols s address rd ack data /// p 7 bits 8 bits wr s ack command ack p 8 bits address 7 bits p 1 ack data 8 bits ack command 8 bits ack wr address 7 bits s s address wr ack command ack s address 7 bits 8 bits 7 bits rd ack data 8 bits /// p
smbus digital interface from a software perspective, the MAX6640 appears as a set of byte-wide registers. this device uses a stan- dard smbus 2-wire/i 2 c-compatible serial interface to access the internal registers. the MAX6640 employs four standard smbus protocols: write byte, read byte, send byte, and receive byte (figures 1, 2, and 3). the shorter receive byte protocol allows quicker transfers, provided that the correct data register was previously selected by a read byte instruc- tion. use caution with the shorter protocols in multimas- ter systems, since a second master could overwrite the command byte without informing the first master. table 3 details the register addresses and functions, whether they can be read or written to, and the power- on reset (por) state. see tables 4? for all other regis- ter functions and the register descriptions section. temperature reading temperature data can be read from registers 00h and 01h. the temperature data format for these registers is 8 bits, with the lsb representing 1? (table 1) and the msb representing +128?. the msb is transmitted first. three additional temperature bits provide resolution down to 0.125 c and are in the channel 1 extended temperature (05h) and channel 2 extended tempera- ture (06h) registers. all values below 0? clip to 00h. the MAX6640 employs a register lock mechanism to avoid getting temperature results from the temperature register and the extended temperature register sam- pled at two different time points. reading the extended register stops the MAX6640 from updating the temper- ature register for at least 0.25s, unless there is a tem- MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller _______________________________________________________________________________________ 7 scl a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave ab cd e fg hij sda t su:sta t hd:sta t low t high t su:dat t su:sto t buf lm k e = slave pulls smbdata line low f = acknowledge bit clocked into master g = msb of data clocked into slave h = lsb of data clocked into slave i = master pulls data line low j = acknowledge clocked into slave k = acknowledge clock pulse l = stop condition m = new start condition figure 2. smbus write timing diagram scl ab cd e fg h i j k sda t su:sta t hd:sta t low t high t su:dat t hd:dat t su:sto t buf a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave e = slave pulls smbdata line low l m f = acknowledge bit clocked into master g = msb of data clocked into master h = lsb of data clocked into master i = master pulls data line low j = acknowledge clocked into slave k = acknowledge clock pulse l = stop condition m = new start condition figure 3. smbus read timing diagram i 2 c is a trademark of philips corp. purchase of i 2 c components of maxim integrated products, inc., or one of its sublicensed associated companies, conveys a license under the philips i 2 c patent rights to use these compo- nents in an i 2 c system, provided that the system conforms to the i 2 c standard specification as defined by philips.
MAX6640 perature register read before the scheduled update. this allows enough time to read the main register before it is updated, thereby preventing reading the temperature register data from one conversion and the extended temperature register data from a different conversion. the MAX6640 measures the temperature at a fixed rate of 4hz immediately after it is powered on. setting bit 7 of the configuration register (04h) shuts down the tem- perature measurement cycle. ot output when a measured temperature exceeds the corre- sponding ot temperature threshold and ot is not masked, the associated ot status register bit sets and the ot output asserts. if ot for the respective channel is masked, the ot status register sets, but the ot out- put does not assert. to deassert the ot output and the associated status register bit, either the measured tem- perature must fall at least 5 c below the trip threshold or the trip threshold must be increased to at least 5 c above the current measured temperature. therm when a measured temperature exceeds the corre- sponding therm temperature threshold and therm is not masked, the associated therm status register bit is set and the therm output asserts. if therm for the respective channel is masked, the therm status regis- ter is set, but the therm output does not assert. to deassert the therm output and the associated status register bit, either the measured temperature must fall at least 5 c below the trip threshold or the trip thresh- old must be increased to at least 5 c above the current measured temperature. asserting therm internally or externally forces both pwm outputs to 100% duty cycle when bit 6 in address 13h (fan 1) or bit 6 in address 17h (fan 2) is set. alert the alert output asserts to indicate that a measured temperature exceeds the alert trip threshold for that temperature channel. the status bit and the alert out- put clear by reading the alert status register. if the alert status bit is cleared, but the temperature still exceeds the alert temperature threshold, alert reasserts on the next conversion, and the status bit sets again. a successful alert response protocol clears alert , but does not affect the alert status bit. tach1 and tach2 inputs to measure the fan speed, the MAX6640 has two tachometers. each tachometer has an accurate internal clock to count the time elapsed in one revolution. therefore, it is counting the time between two tachome- ter pulses for a fan with four poles. when the pwm sig- nal is used to directly modulate the fan? power supply, the pwm frequency is normally in the 20hz to 100hz range. in this case, the time required for one revolution may be longer than the pwm on-time. for this reason, the pwm pulses are periodically stretched to allow tachometer measurement over a full revolution. turn off pulse stretching by setting bit 5 of register 13h or regis- ter 17h when using a 4-wire fan. the tachometer count is inversely proportional to the fan? rpm. the tachometer count data is stored in regis- ter 20h (for tach1) and register 21h (for tach2). reading a value of 255 from the tach count register means the fan? rpm is zero or too slow for the range. reading a value of zero in the tach count register means the fan? rpm is higher than the range selected. table 2 shows the fan? available rpm ranges. use reg- isters 10h or 14h to select the appropriate rpm range for the fan being used. fanfail the fanfail output asserts to indicate that one of the fans has failed or is spinning slower than the required speed. the MAX6640 detects fan fault depending on the fan control mode. in pwm mode, the MAX6640 pro- duces a square wave with a duty cycle set by the value written to the duty-cycle registers (26h and 27h). in this mode, the MAX6640 signals a fan fault when the tachometer count is greater than the maximum tachometer count value stored in the appropriate regis- ter (22h and 23h). after the MAX6640 asserts fan 2-channel temperature monitor with dual automatic pwm fan-speed controller 8 _______________________________________________________________________________________ temp ( c) temp ( c) digital output 241 +241 1111 0001 240 +240 1111 0000 126 +126 0111 1110 25 +25 0001 1001 1.50 1 0000 0001 0.00 0 0000 0000 table 1. temperature data byte format fan rpm range internal clock frequency (khz) 2000 1 4000 2 8000 4 16,000 8 table 2. tachometer setting
fail , the fan with a tachometer fault goes to full speed for 2s in an attempt to restart the fan and then returns to the original duty-cycle settings. reading the status register clears the fanfail status bits and the output. the MAX6640 measures the fan speed again after 2s. the MAX6640 asserts fanfail if it detects the fan fault again. in rpm mode (either automatic or manual), the MAX6640 checks for fan failure only when the duty cycle reaches 100%. it asserts fanfail when the tachometer count is greater than twice the target tachometer count. in manual rpm mode, registers 22h and 23h store the target tachometer count value. in automatic rpm mode, these registers store the maxi- mum tachometer count. fan-speed control the MAX6640 adjusts fan speed by controlling the duty cycle of a pwm signal. this pwm signal then either modulates the dc brushless fan? power supply or dri- ves a speed-control input on a fan that is equipped with one. there are three speed-control modes: pwm , in which the pwm duty cycle is directly programmed over the smbus; manual rpm , in which the desired tachometer count is programmed into a register and the MAX6640 adjusts its duty cycle to achieve the desired tachometer count; and automatic rpm , in which the tachometer count is adjusted based on a programmed temperature profile. the MAX6640 divides each pwm cycle into 120 time slots. registers 26h and 27h contain the current values of the duty cycles for pwm1 and pwm2, expressed as the effective time slot length. for example, the pwm1 output duty cycle is 25% when register 26h reads 1eh (30/120). pwm control mode enter pwm mode by setting bit 7 of the fan 1 or 2 con- figuration 1 register (10h and 14h) to 1. in pwm control mode, the MAX6640 generates pwm signals whose duty cycles are specified by writing the desired values to fan duty-cycle registers 26h and 27h. when a new duty-cycle value is written into one of the fan duty-cycle registers, the duty cycle changes to the new value at a rate determined by the rate-of-change bits [6:4] in the fan 1 or 2 configuration 1 register. the rate-of-change of the duty cycle ranges from 000 (immediately changes to the new programmed value) to 111 (changes by 1/120 every 4s). see table 4 and the fan 1 and 2 configuration 1 (10h and 14h) section. manual rpm control mode enter manual rpm control mode by setting bits 2, 3, and 7 of the fan 1 or 2 configuration 1 register (10h and 14h) to zero. in the manual rpm control mode, the MAX6640 adjusts the duty cycle and measures the fan speed. enter the target tachometer count in register 22h for fan 1 and register 23h for fan 2. the MAX6640 compares the target tachometer count with the mea- sured tachometer count and adjusts the duty cycle so that the fan speed gradually approaches the target tachometer count. the first time manual rpm control mode is entered, the initial pwm duty cycle is determined by the target tachometer count: where targettach is the value of the target tachometer count in the target tach count register (22h or 23h). if the initial duty cycle value is over 120, the duty cycle is 100%. if spin-up is enabled (bit 7 in registers 13h and 17h) and the fan is not already spinning, the duty cycle first goes to 100% and then goes to the initial duty-cycle value. every 2s, the MAX6640 counts the fan? period by counting the number of pulses stored in registers 24h and 25h. if the count is different from the target count, the duty cycle is adjusted. if a nonzero rate-of-change is selected, the duty cycle changes at the specified rate until the tachometer count is within 5 of the target. then the MAX6640 gets into a locked state and updates the duty cycle every 2s. automatic rpm control mode in the automatic rpm control mode, the MAX6640 mea- sures temperature, sets a target tachometer count based on the measured temperature, and then adjusts the duty cycle so the fan spins at the desired speed. enter this mode by setting bit 7 of the fan 1 or 2 config- uration 1 register (10h and 14h) to zero and selecting the temperature channel that controls the fan speed using bits 2 and 3 of the configuration register. in both the rpm modes (automatic and manual), the MAX6640 implements a low limit for the tachometer counts. this limits the maximum speed of the fan by ensuring that the fan? tachometer count does not go lower than the tachometer count specified by bits 5 through 0 of register 24h for fan 1 and register 25h for fan 2. typical values for the minimum tachometer count are 30h to 60h. set the value to correspond to the full- rated rpm of the fan. see figure 4. figure 5 shows how the MAX6640 calculates the target tachometer value based on the measured temperature. at t min , the fan spins at a minimum speed value corre- sponding to the maximum tachometer count value initial duty cycle t ettach arg = ? 255 2 MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller _______________________________________________________________________________________ 9
MAX6640 stored in register 22h or 23h. bit 0 of register 11h (fan 1) and register 15h (fan 2) selects the behavior below t min . if bit 0 is equal to zero, the fan will be completely off below t min . when the temperature is falling, it must drop 5 c below t min before the fan turns off. if bit 0 is set to 1, the fan does not turn off below t min , but instead stays at the maximum tachometer count in reg- ister 22h or 23h. when the measured temperature is higher than t min , the MAX6640 calculates the target tachometer count value based on two linear equations. the target tachometer count decreases by the tach step size value stored in bits 7 through 4 of registers 11h and 15h each time the measured temperature increases by the temperature step size value stored in bits 2 and 3 of registers 11h and 15h. as the measured temperature continues to increase, a second tachometer step size goes into effect. bits 3 through 0 of register 12h and 16h select the number temperature/pwm steps after which the new step size takes effect. the new step size is selected by bits 7 to 4 of registers 12h and 16h. register descriptions channel 1 and channel 2 temperature registers (00h and 01h) these registers contain the results of temperature mea- surements. the msb has a weight of +128 c and the lsb +1 c. temperature data for remote diode 1 is in the channel 1 temperature register. temperature data for remote diode 2 or the local sensor (selectable by bit 4 in the global configuration register) is in the channel 2 temperature register. three additional temperature bits provide resolution down to 0.125 c and are in the channel 1 extended temperature (05h) and channel 2 extended temperature (06h) registers. the channel 1 and channel 2 temperature registers do not update until at least 250ms after the access of the associated extended temperature registers. all values below 0c return 00h. status register (02h) a 1 indicates that an alert , therm , ot , or fan fault has occurred. reading this register clears bits 7, 6, 1, and 0. reading the register also clears the alert and fanfail outputs, but not the therm and ot outputs. if the fault is still present on the next temperature measure- ment cycle, any cleared bits and outputs are set again. a successful alert response clears the values on the out- puts but does not clear the status register bits. the alert bits assert when the measured temperature is higher than the respective thresholds. the therm and ot outputs behave like comparators with 5 c hysteresis. mask register (03h) this register masks the alert , ot , therm , and fanfail outputs. a 1 prevents the corresponding fail- ures from being asserted on these outputs. the mask bits do not affect the status register. global configuration register (04h) the global configuration register controls the shutdown mode, power-on reset, smbus timeout, and tempera- ture channel 2 source select: d7: run/standby. normal operation is run (0). setting this bit to 1 suspends conversions and puts the MAX6640 into low-power sleep mode. d6: software por. writing a 1 resets all registers to their default values. 2-channel temperature monitor with dual automatic pwm fan-speed controller 10 ______________________________________________________________________________________ t ach max t ach 0xffh t ach min temperature t b t min-5 t min t ach b+1 t ach a+1 figure 4. tachometer target calculation rpm 0 rpm max rpm min temperature t min -5 t min t b t ach a+1 t ach b+1 figure 5. rpm target calculation
MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller ______________________________________________________________________________________ 11 read/ write register no. address por state function d7 d6 d5 d4 d3 d2 d1 d 0 r 00h 0000 0000 temperature channel 1 msb (+128?) ls b ( 1 c ) r 01h 0000 0000 temperature channel 2 msb (+128?) ls b ( 1 c ) r 02h 0000 0000 status byte channel 1 alert channel 2 alert channel 1 ot nn ot nn therm channel 2 therm fan 1 fault fan 2 faul t r/w 03h 0000 0011 output mask channel 1 alert channel 2 alert channel 1 ot nn ot nn therm channel 2 therm fan 1 fault fan 2 faul t r/w 04h 0011 0000 global configuration run un or mu u n t nn u r r r r r nn n u m l r r r r u r nn n u m l r r r r u r nn alert limit msb ls b ( 1 c ) r/w 09h 0101 0101 channel 2 alert limit msb ls b ( 1 c ) r/w 0ah 0110 1110 channel 1 ot limit msb ls b ( 1 c ) r/w 0bh 0110 1110 channel 2 ot limit msb ls b ( 1 c ) r/w 0ch 0101 0101 channel 1 therm limit msb ls b ( 1 c ) r/w 0dh 0101 0101 channel 2 therm limit msb ls b ( 1 c ) r/w 10h 1000 0010 fan 1 configuration 1 pwm mode step-size delay (msb) step-size delay step-size delay (lsb) fan 1 channel 1 control fan 1 channel 2 control rpm range select rp m r ang e sel ect r/w 11h 0000 0000 fan 1 configuration 2a rpm step- size a (msb) rpm step- size a rpm step- size a rpm step- size a (lsb) temp step-size a (msb) temp step-size a (lsb) pwm 100% duty cycle m i ni m um fan sp eed 0 = 0%, 1= val ue table 3. register map
MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller 12 ______________________________________________________________________________________ read/ write register no. address por state function d7 d6 d5 d4 d3 d2 d1 d 0 r/w 12h 0000 0000 fan 1 configuration 2b rpm step- size b (msb) rpm step- size b rpm step- size b rpm step-size b (lsb) start step-size b (msb) start step-size b start step- size b s tar t step - si ze b ( ls b) r/w 13h 0100 0001 fan 1 configuration 3 spin-up disable therm to full-speed enable pulse stretching disable reserved reserved reserved fan pwm frequency (msb) fan p wm fr eq uency ( lsb) r/w 14h 1000 0010 fan 2 configuration 1 pwm mode step-size delay (msb) step-size delay step-size delay (lsb) fan 2 channel 1 control fan 2 channel 2 control rpm range select rp m r ang e sel ect r/w 15h 0000 0000 fan 2 configuration 2a rpm step- size a (msb) rpm step- size a rpm step- size a rpm step-size a (lsb) temp step-size a (msb) temp step-size a (lsb) pwm 100% duty cycle m i ni m um fan sp eed 0 = 0%, 1= val ue in 22h r/w 16h 0000 0000 fan 2 configuration 2b rpm step- size b (msb) rpm step- size b rpm step- size b rpm step-size b (lsb) start step-size b (msb) start step-size b start step- size b s tar t step - si ze b ( ls b) r/w 17h 0100 0001 fan 2 configuration 3 spin-up disable therm to full-speed enable pulse stretching disable reserved reserved reserved fan pwm frequency (msb) fan p wm fr eq uency ( lsb) r 20h 1111 1111 fan 1 tachometer count msb ls b r 21h 1111 1111 fan 2 tachometer count msb ls b r/w 22h 1111 1111 fan 1 max tach count/ target tach count msb ls b r/w 23h 1111 1111 fan 2 max tach count/ target tach count msb ls b r/w 24h 0100 0000 pulses per revolution/ fan 1 minimum tach count pulse per revolution (msb) pulse per revolution (lsb) fan 1 min tach count (msb) fan 1 min tach count fan 1 min tach count fan 1 min tach count fan 1 min tach count fan 1 mi n tach count ( lsb) r/w 25h 0100 0000 pulses per revolution/ fan 2 minimum tach count pulse per revolution (msb) pulse per revolution (lsb) fan 2 min tach count (msb) fan 2 min tach count fan 2 min tach count fan 2 min tach count fan 2 min tach count fan 2 mi n tach count ( lsb) r 26h 0000 0000 fan 1 cur r ent d uty cycl e msb ls b table 3. register map (continued)
d5: smbus timeout disable. writing a zero enables smbus timeout for prevention of bus lockup. when the timeout function is enabled, the smbus interface is reset if sda or scl remains low for more than 74ms (typ). d4: temperature channel 2 source. selects either local or remote 2 as the source for temperature channel 2 register data. writing a zero to this bit selects remote 2 for temperature channel 2. extended temperature registers (05h and 06h) these registers contain the extended temperature data from channels 1 and 2. bits d[7:5] contain the 3 lsbs of the temperature data. the bit values are 0.5 c, 0.25 c, and 0.125 c. when bit 0 is set to 1, a diode fault has been detected. channel 1 and channel 2 alert , ot , and therm limits (08h through 0dh) these registers contain the temperatures above which the alert , therm , and ot status bits set and outputs assert (for the temperature channels that are not masked). the data format is the same as that of the channel 1 and channel 2 temperature registers: the lsb weight is +1 c and the msb is +128 c. fan 1 and 2 configuration 1 (10h and 14h) the following registers control the modes of operation of the MAX6640: d7: pwm mode. d7 = 1 sets the fan into manual pwm duty-cycle control mode. write the target duty cycle in the fan duty-cycle register. d7 = 0 puts the fan into rpm control mode. to set rpm manually, set both fan-control temperature channels (bits d2 and d3) to zero and write the desired tachometer count into the tach count register. d[6:4]: fan duty-cycle rate-of-change. d[6:4] sets the time between increments of the duty cycle. each increment is 1/120 of the duty cycle. by adjust- ing the rate of change, audibility of fan-speed changes can be traded for response time. table 4 shows the effect of d[6:4] and, for reference, the time required for the fan speed to change from 33% to 100% duty cycle as a function of the rate-of- change bits. MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller ______________________________________________________________________________________ 13 read/ write register no. address por state function d7 d6 d5 d4 d3 d2 d1 d 0 w 26h 0011 1100 fan 1 target duty cycle msb ls b r 27h 0000 0000 fan 2 current duty cycle msb ls b w 27h 0011 1100 fan 2 target duty cycle msb ls b r/w 28h 0100 000 channel 1 minimum fan-start temperature msb ls b r/w 29h 0100 0000 channel 2 minimum fan-start temperature msb ls b r 3dh 0101 1000 read device id 01011000 r 3eh 0100 1101 read manufacturer id 01001101 r 3fh 0000 0000 read device revision 00000000 table 3. register map (continued)
MAX6640 d[3:2]: temperature channel(s) for fan control. selects the temperature channel(s) that control the pwm output when the MAX6640 is in automatic rpm control mode (pwm mode bit is zero). if two chan- nels are selected, the fan goes to the higher of the two possible speeds. if neither channel is selected, then the fan is in manual rpm mode and the speed is forced to the value written to the target tach count register 22h or 23h. d[1:0]: rpm range. scales the tachometer counter by setting the maximum (full-scale) value of the rpm range to 2000, 4000, 8000, or 16,000. (table 2 shows the internal clock frequency as a function of the range.) fan 1 and 2 configuration 2a (11h and 15h) the following registers apply to the automatic rpm control mode: d[7:4]: fan rpm (tachometer) step-size a. selects the number of tachometer counts the target value decreases for each temperature step increase above the fan-start temperature. value = n + 1 (1 through 16) where n is the value of d[7:4]. d[3:2]: temperature step size. selects the temper- ature increment for fan control. for each temperature step increase, the target tachometer count decreas- es by the value selected by d[7:4] (table 7). d1: pwm output polarity. pwm output is low at 100% duty cycle when this bit is set to zero. pwm output is high at 100% duty cycle when this bit is set to 1. d0: minimum speed. selects the value of the mini- mum fan speed (when temperature is below the fan- start temperature in the automatic rpm control mode). set to zero for 0% fan drive. set to 1 to deter- mine the minimum fan speed by the tachometer count value in registers 22h and 23h (fan maximum tach). 2-channel temperature monitor with dual automatic pwm fan-speed controller 14 ______________________________________________________________________________________ a c t u a l r a t e o f ch a n g e at spec if i c pw m frequencies register 10h or 14h d[6:4] nominal rate of change (s) 100hz (s) 50hz (s) 33.3hz (s) 20hz (s) nominal time from 33% to 100% (s) 000 0 0000 0 001 0.0625 0.06 0.06 0.06 0.05 5 010 0.125 0.13 0.12 0.12 0.15 10 011 0.25 0.25 0.26 0.24 0.25 20 100 0.5 0.5 0.5 0.51 0.5 40 101 1 1 1 0.99 1 80 110 2 2 2 1.98 2 160 111 4 4 4 3.96 4 320 table 4. fan duty-cycle rate-of-change d[1:0] fan maximum rpm value 00 2000 01 4000 10 8000 11 16,000 table 5. fan rpm speed maximum rpm value actual rpm selected number of pulses per revolution actual fan pulses per revolution tachometer count value* 2000 1000 2 2 3ch 4000 1000 2 2 78h 4000 3000 2 2 28h 4000 3000 2 4 14h 16,000 8000 4 4 3ch 16,000 8000 4 2 78h table 6. rpm to tachometer count relationship examples * tachometer count value = ((internal clock frequency) x 60) / actual rpm) (selected number of pulses per revolution / actual fan pulses)
fan 1 and 2 configuration 2b (12h and 16h) the following registers select the tachometer step sizes and number of steps for step-size a to step-size b slope changes (see figure 1): d[7:4]: rpm (tachometer) step size b. selects number of tachometer counts the target value decreases for each temperature step increase after the number of steps selected by d[3:0]. value = n + 1 (1 through 16) where n is the value of d[7:4]. d[3:0]: selects the number of temperature/tachome- ter steps above the fan-start temperature at which step-size b begins. fan 1 and fan 2 configuration 3 (13h and 17h) the following registers control fan spin-up, pwm output frequency, pulse stretching, and therm to fan full- speed enable: d7: fan spin-up disable. set to zero to enable fan spin-up. whenever the fan starts up from zero drive, it is driven with 100% duty cycle for 2s to ensure that it starts. set to 1 to disable the spin-up function. d6: therm to full-speed enable. when this bit is 1, therm going low (either by being pulled low externally or by the measured temperature exceed- ing the therm limit) forces the fan to full speed. in all modes, this happens at the rate determined by the rate-of-change selection. when therm is deasserted (even if fan has not reached full speed), the speed falls at the selected rate-of-change to the target speed. d5: disable pulse stretching. pulse stretching is enabled when this bit is set to zero. when modulat- ing the fan? power supply with the pwm signal, the pwm pulses are periodically stretched to keep the tachometer signal available for one full revolution. setting this bit to 1 disables pulse stretching. the MAX6640 still measures the fan speed but does not stretch the pulses for measurements, so the fan? power supply must not be pulse modulated. d[1:0]: pwm output frequency. these bits control the pwm output frequency as shown in table 8. fan tach count 1 and 2 (20h and 21h) these registers have the latest tachometer measure- ment of the corresponding channel. this is inversely proportional to the fan? speed. the fan rpm range should be set so this count falls in the 30 to 160 range for normal fan operation. fan start tach count/target tach count (22h and 23h) d[7:0]: this sets the starting tachometer count for the fan in automatic rpm mode. depending on the setting of the minimum duty-cycle bit, the tachometer count has this value either at all temperatures below the fan- start temperature or the count is zero below the fan- start temperature and has this value when the fan-start temperature is reached. these registers are the target tach count when in manual rpm mode. fan 1 and 2 pulses and min rpm (24h and 25h) d[7:6]: this sets the number of tachometer pulses per revolution for the fan. when set properly, a 2000rpm fan with two pulses per revolution has the same tachometer count as a 2000rpm fan with four pulses per revolution. table 9 lists tachometer pulses per revolution. d[5:0]: this sets the minimum allowable fan tachometer count (maximum speed). this limits the maximum speed of the fan to reduce noise at high temperatures. for reasonable speed resolution, the fan rpm range should be set so this value is between about 30 and 60. if a maximum rpm limit is unnecessary, this value can be set to the full-speed tachometer count. fan 1 and 2 duty cycle (26h and 27h) these registers contain the present value of the pwm duty cycle. in pwm fan-control mode, the desired (tar- get) value of the pwm duty cycle can be written directly into this register. channel 1 and channel 2 fan-start temperature (28h and 29h) these registers contain the temperatures at which fan control begins (in automatic rpm mode). MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller ______________________________________________________________________________________ 15 d[3:2] fan control temperature step size ( c) 00 1 01 2 10 4 11 8 table 7. temperature step size d[1:0] low frequency (hz) 00 20 01 33.33 10 50 11 100 table 8. fan pwm frequency
MAX6640 applications information fan-drive circuits a variety of fan-drive circuit configurations can be used with the MAX6640 to control the fan? speed. four of the most common are shown in figures 6 through 10. pwm power-supply drive (high side or low side) the simplest way to control the speed of a 3-wire (sup- ply, ground, and tachometer output) fan is to modulate its power supply with a pwm signal. the pwm frequen- cy is typically in the 20hz to 40hz range, with 33hz being a common value. if the frequency is too high, the fan? internal control circuitry does not have sufficient time to turn on during a power-supply pulse. if the fre- quency is too low, the power-supply modulation becomes more easily audible. the pwm can take place on the high side (figure 6) or the low side (figure 7) of the fan? power supply. in either case, if the tachometer is used, it is usually nec- essary to periodically stretch a pwm pulse so there is enough time to count the tachometer pulse edges for speed measurement. the MAX6640 allows this pulse stretching to be enabled or disabled to match the needs of the application. pulse stretching can sometimes be audible if the fan responds quickly to changes in the drive voltage. if the acoustic effects of pulse stretching are too noticeable, the circuit in figure 8 can be used to eliminate pulse stretching while still allowing accurate tachometer feed- back. the diode connects the fan to a low-voltage power supply, which keeps the fan? internal circuitry powered even when the pwm drive is zero. therefore, the tachometer signal is always available and pulse stretching can be turned off. note that this approach prevents the fan from turning completely off, so even when the duty cycle is 0%, the fan may still spin. linear fan supply drive while many fans are compatible with pwm power-supply drive, some are excessively noisy with this approach. when this is the case, a good alternative is to control the fan? power-supply voltage with a variable dc power- supply circuit. the circuit in figure 9 accepts the pwm signal as an input, filters the pwm, and converts it to a dc voltage that then drives the fan. to minimize the size of the filter capacitor, use the highest available pwm fre- quency. pulse stretching is not necessary when using a linear fan supply. note that this approach is not as effi- cient as pwm drive, as the fan? power-supply current flows through the mosfet, which can have an apprecia- ble voltage across it. the total power is still less than that of a fan running at full speed. table 10 is a summa- ry of fan-drive options. 2-channel temperature monitor with dual automatic pwm fan-speed controller 16 ______________________________________________________________________________________ d[7:6] tachometer pulses per revolution 00 1 01 2 10 3 11 4 table 9. tachometer pulses per revolution v cc pwm1 4.7k ? 4.7k ? t ach1 3v to 5.5v t ach output v fan (5v or 12v) figure 6. high-side pwm drive circuit v cc t ach1 4.7k ? 4.7k ? pwm1 3v to 5.5v 3v to 5.5v t ach output v fan (5v or 12v) figure 7. low-side drive circuit
4-wire fans some fans have an additional, fourth terminal that accepts a logic-level pwm speed-control signal as shown in figure 10. these fans require no external power circuitry and combine the low noise of linear drive with the high efficiency of pwm power-supply drive. higher pwm frequencies are recommended when using 4-wire fans. quick-start guide for 8000rpm 4-pole (2 pulses per revolution) fan in automatic rpm mode using the circuit of figure 7 1) write 02h to register 11h to set the pwm output to drive the n-channel mosfet. 2) write 4bh to register 22h to set the minimum rpm to 3200. 3) write 5eh to register 24h to set the pulses per revo- lution to 2 and to set the maximum rpm speed to 8000rpm. 4) write 19h to register 28h to set the fan-start temper- ature to +25?. 5) write d2h to register 10h to start automatic rpm mode. remote-diode considerations temperature accuracy depends upon having a good- quality, diode-connected, small-signal transistor. accuracy has been experimentally verified for all the devices listed in table 11. the MAX6640 can also directly measure the die temperature of cpus and other ics with on-board temperature-sensing diodes. the transistor must be a small-signal type with a rela- tively high forward voltage. this ensures that the input voltage is within the a/d input voltage range. the for- ward voltage must be greater than 0.25v at 10? at the highest expected temperature. the forward voltage must be less than 0.95v at 100? at the lowest expect- ed temperature. the base resistance has to be less than 100 ? . tight specification of forward-current gain (+50 to +150, for example) indicates that the manufac- turer has good process control and that the devices have consistent characteristics. MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller ______________________________________________________________________________________ 17 v cc pwm1 4.7k ? 4.7k ? t ach1 3v to 5.5v 3v to 5.5v t ach output v f an (5v or 12v) figure 10. 4-wire fan with pwm speed-control input v cc pwm1 4.7k ? 4.7k ? t ach1 3v to 5.5v t ach output v f an (12v or 5v) 5v figure 8. high-side pwm drive with ?eep-alive?supply v cc pwm1 t ach1 4.7k ? 3v to 5v 4.7k ? 100k ? 91k ? 33k ? 100k ? 3.3v 2n3904 2.2 f 10 f t ach output v fan (5v or 12v) t ach output figure 9. high-side linear drive circuit
MAX6640 effect of ideality factor the accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote diode (actually a transistor). the MAX6640 is optimized for n = 1.008, which is the typical value for the intel pentium?iii and the amd athlon mp model 6. if a sense transistor with a different ideality factor is used, the output data is different. fortunately, the difference is predictable. assume a remote-diode sensor designed for a nominal ideality factor n nominal is used to measure the tem- perature of a diode with a different ideality factor, n 1 . the measured temperature t m can be corrected using: where temperature is measured in kelvin. as mentioned above, the nominal ideality factor of the MAX6640 is 1.008. as an example, assume the MAX6640 is configured with a cpu that has an ideality factor of 1.002. if the diode has no series resistance, the measured data is related to the real temperature as follows: for a real temperature of +85? (358.15k), the mea- sured temperature is +82.91? (356.02k), which is an error of -2.13?. effect of series resistance series resistance in a sense diode contributes addition- al errors. for nominal diode currents of 10? and 100?, change in the measured voltage is: ? v m = r s (100? - 10?) = 90? x r s since 1? corresponds to 198.6?, series resistance contributes a temperature offset of: assume that the diode being measured has a series resistance of 3 ? . the series resistance contributes an offset of: the effects of the ideality factor and series resistance are additive. if the diode has an ideality factor of 1.002 and series resistance of 3 ? , the total offset can be cal- culated by adding error due to series resistance with error due to ideality factor: 1.36? - 2.13? = -0.77? for a diode temperature of +85?. in this example, the effect of the series resistance and the ideality factor partially cancel each other. for best accuracy, the discrete transistor should be a small-signal device with its collector connected to gnd and base connected to dxn. table 11 lists examples of discrete transistors that are appropriate for use with the MAX6640. 30 453 1 36 ? ? = . . c c 90 198 6 0 453 ? = ? v v c c . . tt n n tt actual m nominal mm = ? ? ? ? ? ? = ? ? ? ? ? ? = 1 1 008 1 002 1 00599 . . (. ) tt n n m actual nominal = ? ? ? ? ? ? 1 2-channel temperature monitor with dual automatic pwm fan-speed controller 18 ______________________________________________________________________________________ figure description pulse stretching pwm frequency pwm polarity 6 high-side pwm drive yes low negative 7 low-side pwm drive yes low positive 8 high-side pwm drive with keep-alive supply no low negative 9 high-side linear supply no high positive 10 4-wire fan with pwm speed-control input no high positive table 10. summary of fan-drive options manufacturer model no. central semiconductor (usa) cmpt3906 rohm semiconductor (usa) sst3906 samsung (korea) kst3906-tf siemens (germany) smbt3906 table 11. remote-sensor transistor manufacturers intel and pentium are registered trademarks of intel corp.
the transistor must be a small-signal type with a rela- tively high forward voltage; otherwise, the adc input voltage range can be violated. the forward voltage at the highest expected temperature must be greater than 0.25v at 10?, and at the lowest expected tempera- ture, the forward voltage must be less than 0.95v at 100?. large-power transistors must not be used. also, ensure that the base resistance is less than 100 ? . tight specifications for forward current gain (50 < ?< 150, for example) indicate that the manufacturer has good process controls and that the devices have consistent v be characteristics. adc noise filtering the integrating adc has inherently good noise rejec- tion, especially of low-frequency signals such as 60hz/120hz power-supply hum. micropower operation places constraints on high-frequency noise rejection. lay out the pc board carefully with proper external noise filtering for high-accuracy remote measurements in electrically noisy environments. filter high-frequency electromagnetic interference (emi) at dxp and dxn with an external 2200pf capaci- tor connected between the two inputs. this capacitor can be increased to about 3300pf (max), including cable capacitance. a capacitance higher than 3300pf introduces errors due to the rise time of the switched- current source. twisted pairs and shielded cables for remote-sensor distances longer than 8in, or in par- ticularly noisy environments, a twisted pair is recom- mended. its practical length is 6ft to 12ft (typ) before noise becomes a problem, as tested in a noisy elec- tronics laboratory. for longer distances, the best solu- tion is a shielded twisted pair like that used for audio microphones. for example, belden #8451 works well for distances up to 100ft in a noisy environment. connect the twisted pair to dxp and dxn and the shield to ground, and leave the shield? remote end unterminated. excess capacitance at dxn or dxp limits practical remote-sensor distances (see the typical operating characteristics ). for very long cable runs, the cable? parasitic capaci- tance often provides noise filtering, so the recommend- ed 2200pf capacitor can often be removed or reduced in value. cable resistance also affects remote-sensor accuracy. a 1 ? series resistance introduces about +1/2? error. pc board layout checklist 1) place the MAX6640 as close as practical to the remote diode. in a noisy environment, such as a computer motherboard, this distance can be 4in to 8in, or more, as long as the worst noise sources (such as crts, clock generators, memory buses, and isa/pci buses) are avoided. 2) do not route the dxp/dxn lines next to the deflection coils of a crt. also, do not route the traces across a fast memory bus, which can easily introduce +30? error, even with good filtering. otherwise, most noise sources are fairly benign. 3) route the dxp and dxn traces parallel and close to each other, away from any high-voltage traces such as +12vdc. avoid leakage currents from pc board contamination. a 20m ? leakage path from dxp ground causes approximately +1? error. 4) connect guard traces to gnd on either side of the dxp/dxn traces. with guard traces, placing routing near high-voltage traces is no longer an issue. 5) route as few vias and crossunders as possible to minimize copper/solder thermocouple effects. 6) when introducing a thermocouple, make sure that both the dxp and the dxn paths have matching thermocouples. in general, pc board-induced ther- mocouples are not a serious problem. a copper solder thermocouple exhibits 3v/?, and it takes approximately 200? of voltage error at dxp/dxn to cause a +1? measurement error, so most para- sitic thermocouple errors are swamped out. 7) use wide traces. narrow traces are more inductive and tend to pick up radiated noise. the 10-mil widths and spacings recommended are not absolutely nec- essary (as they offer only a minor improvement in leakage and noise), but use them where practical. 8) placing an electrically clean copper ground plane between the dxp/dxn traces and traces carrying high-frequency noise signals helps reduce emi. MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller ______________________________________________________________________________________ 19
MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller 20 ______________________________________________________________________________________ MAX6640 v fan sda scl pwm2 dxp1 dxn to clock throttle to system shutdown to smbus master 3.3v to 5.5v 3.3v to 5.5v 3.3v to 5.5v 3.3v to 5.5v 3.3v to 5.5v 3.3v to 5.5v pwm1 5v 5v dxp2 gpu v cc cpu gnd 5v t ach1 t ach2 alert therm f anfail v fan (5v to 12v) ot t ypical operating circuit chip information transistor count: 39,135 process: bicmos
MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller ______________________________________________________________________________________ 21 qfn thin.eps d2 (nd-1) x e e d c pin # 1 i.d. (ne-1) x e e/2 e 0.08 c 0.10 c a a1 a3 detail a e2/2 e2 0.10 m c a b pin # 1 i.d. b 0.35x45 d/2 d2/2 l c l c e e l c c l k l l detail b l l1 e xxxxx marking h 1 2 21-0140 package outline, 16, 20, 28, 32, 40l thin qfn, 5x5x0.8mm -drawing not to scale- l e/2 common dimensions 3.35 3.15 t2855-1 3.25 3.35 3.15 3.25 max. 3.20 exposed pad variations 3.00 t2055-2 3.10 d2 nom. min. 3.20 3.00 3.10 min. e2 nom. max. ne nd pkg. codes 1. dimensioning & tolerancing conform to asme y14.5m-1994. 2. all dimensions are in millimeters. angles are in degrees. 3. n is the total number of terminals. 4. the terminal #1 identifier and terminal numbering convention shall conform to jesd 95-1 spp-012. details of terminal #1 identifier are optional, but must be located within the zone indicated. the terminal #1 identifier may be either a mold or marked feature. 5. dimension b applies to metallized terminal and is measured between 0.25 mm and 0.30 mm from terminal tip. 6. nd and ne refer to the number of terminals on each d and e side respectively. 7. depopulation is possible in a symmetrical fashion. 8. coplanarity applies to the exposed heat sink slug as well as the terminals. 9. drawing conforms to jedec mo220, except exposed pad dimension for t2855-1, t2855-3, and t2855-6. notes: symbol pkg. n l1 e e d b a3 a a1 k 10. warpage shall not exceed 0.10 mm. jedec t1655-1 3.20 3.00 3.10 3.00 3.10 3.20 0.70 0.80 0.75 4.90 4.90 0.25 0.25 0 -- 4 whhb 4 16 0.35 0.30 5.10 5.10 5.00 0.80 bsc. 5.00 0.05 0.20 ref. 0.02 min. max. nom. 16l 5x5 3.10 t3255-2 3.00 3.20 3.00 3.10 3.20 2.70 t2855-2 2.60 2.60 2.80 2.70 2.80 l 0.30 0.50 0.40 -- - -- - whhc 20 5 5 5.00 5.00 0.30 0.55 0.65 bsc. 0.45 0.25 4.90 4.90 0.25 0.65 - - 5.10 5.10 0.35 20l 5x5 0.20 ref. 0.75 0.02 nom. 0 0.70 min. 0.05 0.80 max. -- - whhd-1 28 7 7 5.00 5.00 0.25 0.55 0.50 bsc. 0.45 0.25 4.90 4.90 0.20 0.65 - - 5.10 5.10 0.30 28l 5x5 0.20 ref. 0.75 0.02 nom. 0 0.70 min. 0.05 0.80 max. -- - whhd-2 32 8 8 5.00 5.00 0.40 0.50 bsc. 0.30 0.25 4.90 4.90 0.50 - - 5.10 5.10 32l 5x5 0.20 ref. 0.75 0.02 nom. 0 0.70 min. 0.05 0.80 max. 0.20 0.25 0.30 down bonds allowed no yes 3.10 3.00 3.20 3.10 3.00 3.20 t2055-3 3.10 3.00 3.20 3.10 3.00 3.20 t2055-4 t2855-3 3.15 3.25 3.35 3.15 3.25 3.35 t2855-6 3.15 3.25 3.35 3.15 3.25 3.35 t2855-4 2.60 2.70 2.80 2.60 2.70 2.80 t2855-5 2.60 2.70 2.80 2.60 2.70 2.80 t2855-7 2.60 2.70 2.80 2.60 2.70 2.80 3.20 3.00 3.10 t3255-3 3.20 3.00 3.10 3.20 3.00 3.10 t3255-4 3.20 3.00 3.10 no no no no no no no no yes yes yes yes 3.20 3.00 t1655-2 3.10 3.00 3.10 3.20 yes no 3.20 3.10 3.00 3.10 t1655n-1 3.00 3.20 3.35 3.15 t2055-5 3.25 3.15 3.25 3.35 yes 3.35 3.15 t2855n-1 3.25 3.15 3.25 3.35 no 3.35 3.15 t2855-8 3.25 3.15 3.25 3.35 yes 3.20 3.10 t3255n-1 3.00 no 3.20 3.10 3.00 l 0.40 0.40 ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** see common dimensions table 0.15 11. marking is for package orientation reference only. h 2 2 21-0140 package outline, 16, 20, 28, 32, 40l thin qfn, 5x5x0.8mm -drawing not to scale- 12. number of leads shown are for reference only. 3.30 t4055-1 3.20 3.40 3.20 3.30 3.40 ** yes 0.05 00.02 0.60 0.40 0.50 10 ----- 0.30 40 10 0.40 0.50 5.10 4.90 5.00 0.25 0.35 0.45 0.40 bsc. 0.15 4.90 0.25 0.20 5.00 5.10 0.20 ref. 0.70 min. 0.75 0.80 nom. 40l 5x5 max. 13. lead centerlines to be at true position as defined by basic dimension "e", 0.05. package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .)
MAX6640 2-channel temperature monitor with dual automatic pwm fan-speed controller maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 22 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2004 maxim integrated products printed usa is a registered trademark of maxim integrated products. package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .) qsop.eps e 1 1 21-0055 package outline, qsop .150", .025" lead pitch

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