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ltc2995 1 2995f typical application features description temperature sensor and dual voltage monitor with alert outputs the ltc ? 2995 is a high accuracy temperature sensor and dual supply monitor. it converts the temperature of an external diode sensor and/or its own die temperature to an analog output voltage while rejecting errors due to noise and series resistance. two supply voltages and the measured temperature are compared against upper and lower limits set with resistive dividers. if a threshold is exceeded, the device communicates an alert by pulling low the correspondent open drain logic output. the ltc2995 gives 1c accurate temperature results using commonly available npn or pnp transistors or temperature diodes built into modern digital devices. volt- ages are monitored with 1.5% accuracy. a 1.8v reference output simplifies threshold programming and can be used as an adc reference input. the ltc2995 provides an accurate, low power solution for temperature and voltage monitoring in a compact 3mm 3mm qfn package. dual ov/uv supply and single ot/ut remote temperature monitor applications n monitors temperature and two voltages n voltage output proportional to temperature n adjustable thresholds for temperature and voltage n 1c remote temperature accuracy n 2c internal temperature accuracy n 1.5% voltage threshold accuracy n 3.5ms update time n 2.25v to 5.5v supply voltage n input glitch rejection n adjustable reset timeout n 220a quiescent current n open drain alert outputs n available in 3mm 3mm qfn package n network servers n core, i/o voltage monitors n desktop and notebook computers n environmental monitoring l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. v ptat vs remote diode temperature remote diode temperature (c) C50 0.8 v ptat (v) 1.0 1.2 1.4 050 100 150 2995 ta01b 1.6 1.8 C25 25 75 125 v cc ps ds vh1 vl1 vh2 vl2 v ptat to2 to1 ov uv d + d C ltc2995 2.5v 1.2v 0.1f 64.4k 10.2k 45.3k 2995 ta01a vt1 vt2 gnd tmr v ref 20k 20k 140k 470pf temperature sensor asic system monitor ot t > 125c 4mv/k ut t < 75c +10% C10% 45.3k 10.2k 194k 5nf
ltc2995 2 2995f pin configuration absolute maximum ratings (notes 1, 2) 20 19 18 17 16 7 8 top view 21 ud package 20-lead (3mm 3mm) plastic qfn 9 10 vl1 vh2 vl2 vt2 vt1 uv ov to2 t01 v ref vh1 ps ds gnd tmr d + d C v ptat v cc gnd 12 11 13 14 15 4 5 3 2 1 6 t jmax = 150c, ja = 59c/w exposed pad pcb ground connected optional symbol parameter conditions min typ max units v cc supply voltage l 2.25 5.5 v uvlo supply undervoltage lockout threshold v cc falling l 1.7 1.9 2.1 v i cc average supply current l 220 300 a temperature measurement v ref reference voltage ltc2995 ltc2995c ltc2995i ltc2995h l l l 1.797 1.793 1.790 1.787 1.8 1.8 1.8 1.8 1.803 1.804 1.807 1.808 v v v v v ref load regulation i load = 200a l 1.5 mv remote diode sense current C8 C192 a order information v cc .............................................................. C0.3v to 6v tmr, d + , d C , ds, ps, v ptat , v ref ........ C0.3v to v cc + 0.3v uv , ov , to1 , t02 .......................................... C0.3v to 6v vh1, vl1, vh2, vl2, vt1, vt2 ..................... C0.3v to 6v operating ambient temperature range ltc2995c ................................................ 0c to 70c ltc2995i ............................................. C40c to 85c ltc 2995h ......................................... C40c to 125c storage temperature range .................. C65c to 150c lead free finish tape and reel part marking* package description temperature range ltc2995cud#pbf ltc2995cud#trpbf lfqv 20-lead (3mm 3mm) plastic qfn 0c to 70c ltc2995iud#pbf ltc2995iud#trpbf lfqv 20-lead (3mm 3mm) plastic qfn C40c to 85c ltc2995hud#pbf ltc2995hud#trpbf lfqv 20-lead (3mm 3mm) plastic qfn C40c to 125c consult ltc marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a la bel on the shipping container. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c, v cc = 3.3v, unless otherwise noted.
ltc2995 3 2995f electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c, v cc = 3.3v, unless otherwise noted. note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: all currents into pins are positive; all voltages are referenced to gnd unless otherwise noted. note 3: remote diode temperature, not ltc2995 temperature. note 4: guaranteed by design and test correlation. symbol parameter conditions min typ max units t conv temperature update interval l 3.5 5 ms k t v ptat slope ideality factor = 1.004 4mv/k v ptat load regulation i load = 200a 1.5 mv t int internal temperature accuracy t amb = C40c to 125c 0.5 2 1 c c t rmt remote temperature error, = 1.004 0c to 85c (notes 3, 4) C40c to 0c (notes 3, 4) 85c to 125c (notes 3, 4) 0.25 0.25 0.25 1 1.5 1.5 c c c temperature noise 0.15 0.01 c rms c rms / hz t vcc temperature error vs supply l 0.5 c/v t rs series resistance cancellation error r series = 100 l 0.25 1 c temperature and voltage monitoring v uot undervoltage/overvoltage threshold l 492 500 508 mv t off vt1, vt2 offset l C3 C1 1 c t hyst vt1, vt2 temperature hysteresis l 2 5 10 c t uod uv, ov input 5mv above/below threshold l 0.5 2 ms i in vh1, vl1, vh2, vl2, vt1, vt2, input current l 20 na t uoto uv / ov time-out-period c tmr = tmr open c tmr = 1nf l 5 0.5 10 20 ms ms i tmr tmr current l 2.5 a three state pins ds, ps v ds,ps(h,th) ps, ds input high threshold l v cc C 0.4 v cc C 0.1 v v ds,ps(h,tl) ps, ds input low threshold l 0.1 0.4 v i ds,ps(in,hl) ps, ds high, low input current ds, ps at 0v or v cc l 4 a i ds,ps(in,z) allowable leakage current l 1 a digital outputs v oh high level output voltage, to1 , to2 , uv , ov i = C0.5a l v cc C 1.2 v v ol low level output voltage, to1 , to2 , uv , ov i = 3ma l 0.4 v
ltc2995 4 2995f timing diagrams vln ov v uot 1v t uod t uoto 2995 td02 vhn uv v uot 1v t uod t uod 2995 td03 vln ov v uot 1v t uod t uod 2995 td04 vhn monitor timing vhn monitor timing (tmr pin strapped to v cc ) vln monitor timing vln monitor timing (tmr pin strapped to v cc ) vhn uv v uot 1v t uod t uoto 2995 td01
ltc2995 5 2995f typical performance characteristics remote temperature error vs series resistance remote temperature error vs c decouple (between d + and d C ) temperature error with ltc2995 at same temperature as remote diode remote temperature error vs ambient temperature internal temperature error vs ambient temperature uvlo vs temperature v cc rising, falling buffered reference voltage vs temperature temperature error vs supply voltage v ptat noise vs averaging time t a = 25c, v cc = 3.3v unless otherwise noted. t a (c) C50 C3 t int error (c) C2 0 C1 75 150 100 2995 g03 3 1 2 C25 0 25 50 125 t a (c) C50 C3 t rmt error (c) C2 0 C1 75 150 100 2995 g01 3 1 2 C25 0 25 50 125 t internal = t remote t a (c) C50 C3 t rmt error (c) C2 0 C1 75 150 100 2995 g02 3 1 2 C25 0 25 50 125 t remote = 25c series resistance () 0 C6 error (c) C4 0 C2 800 600 2995 g05 2 6 4 200 400 1200 1000 decouple capacitor (nf) 0 error (c) 0 C2 C4 C6 8 6 2995 g06 4 2 6 24 10 t a (c) C50 uvlo (v) 1.8 2.0 1.6 25 75 150 2995 g08 2.2 0 C25 50 100 125 v cc rising v cc falling t a (c) 1.790 v ref (v) 1.795 2995 g09 1.800 1.810 1.805 C50 25 75 150 0 C25 50 100 125 v cc (v) error (c) C0.2 0 C0.4 C0.6 35 2995 g04 0.2 0.6 0.4 24 6 averaging time (ms) 0.01 0 v ptat noise (c rms) 0.05 0.15 0.20 0.10 1 1000 100 2995 g07 0.1 10
ltc2995 6 2995f typical performance characteristics supply current vs temperature load regulation of v ptat C voltage vs current single wire remote temperature error vs ground noise load regulation of v ref C voltage vs current t a = 25c, v cc = 3.3v unless otherwise noted. delay vs comparator overdrive uv , ov , to1 , to2 vs output sink current reset timeout period vs capacitance overdrive (mv) 0 delay (s) 200 110 2995 g13 800 600 400 1200 1000 100 frequency (khz) 0.1 0.01 absolute temperature error (c) 0.1 110 1000 2995 g12 1 10 100 vac = 50mv p-p tmr pin capacitance (nf) reset timeout t uoto (ms) 0.1 1 10 100 2995 g15 100 10 1 10000 1000 1000 i (ma) v uv / ov / to1 / to2 (v) 0 5 10 15 20 25 30 2995 g14 0.6 0.4 0.2 0 1 0.8 35 load current (ma) 1.78 v ref (v) 1.80 1.79 0 2995 g10 1.82 1.81 C4 C2 2 4 v cc = 2.25v v cc = 3.5v v cc = 4.5v v cc = 5.5v load current (ma) C4 1.14 v ptat (v) 1.18 1.16 C2 0 4 2995 g11 1.20 1.22 2 v cc = 2.25v v cc = 3.5v v cc = 4.5v v cc = 5.5v supply current (a) 240 230 220 2995 g16 250 t a (c) C50 200 210 50 100 C25 0 25 75 125 150
ltc2995 7 2995f pin functions d + : diode sense current source. d + sources the remote diode sensing current. connect d + to the anode of the re- mote sensor device. it is recommended to connect a 470pf bypass capacitor between d + and d C . larger capacitors may cause settling time errors (see typical performance characteristics). if d + i s t i e d t o v cc , the ltc2995 measures the internal sensor temperature. tie d + to v cc if unused. d C : diode sense current sink. connect d C to the cathode of the remote sensor device. tie d C to gnd for single wire remote temperature measurement (see applications information) or internal temperature sensing. ds: diode select input. three state pin that selects tem- perature sensor location. tie ds to v cc to monitor the temperature of the internal diode or to gnd to monitor the temperature of the ex ternal diode. when ds is lef t uncon- nected, the ltc2995 monitors both sensors alternately. if d + is tied to v cc , the ltc2995 measures the internal sensor temperature regardless of the state of ds. exposed pad: exposed pad may be left open or soldered to gnd for better thermal coupling. gnd: device ground ov : overvoltage logic output. open drain logic output that pulls to gnd when either the voltage at vl1 or vl2 is above 0.5v. held low for a programmable delay time set by the capacitor connected to pin tmr. ov has a weak 400k pull-up to v cc and may be pulled above v cc using an external pull-up. leave ov open if unused. ps: polarity select input. selects the polarity of tempera- ture thresholds vt1 and vt2. connect ps to v cc to config- ure vt1 as undertemperature and vt2 as overtemperature threshold. leave ps unconnected to configure both vt1 and vt2 as overtemperature thresholds. connect ps to gnd to configure both vt1 and vt2 as undertemperature thresholds. tie to v cc if temperature thresholds are unused. tmr: reset delay timer. attach an external capacitor (ctmr) to gnd to set the delay time until alerts on to1 , to2 , uv and ov are reset. leaving the pin open generates a minimum delay of 500s. capacitance on this pin adds an additional 8ms/nf reset delay time. tie tmr to v cc to bypass the timer. to1 : temperature logic output 1. open drain logic output that pulls to gnd when v ptat crosses the threshold voltage on pin vt1 with a polarity set by the ps pin (see table 3 in applications information). when v ptat crosses the threshold voltage on pin vt1 with opposite polarity, an additional hysteresis of 20mv is required to release to1 high after a delay adjustable by the capacitor on tmr. to1 has a weak 400k pull-up to v cc and may be pulled above v cc using an external pull-up. leave to1 open if unused. to2 : temperature logic output 2. open drain logic output that pulls to gnd when v ptat crosses the threshold voltage on pin vt2 with a polarity set by the ps pin (see table 3 in applications information). when v ptat crosses the threshold voltage on pin vt2 with opposite polarity, an additional hysteresis of 20mv is required to release to2 high after a delay adjustable by the capacitor on tmr. to2 has a weak 400k pull-up to v cc and may be pulled above v cc using an external pull-up. leave to2 open if unused. uv : undervoltage logic output. open drain logic output that pulls to gnd when either the voltage at vh1 or vh2 is below 0.5v. held low for an adjustable delay time set by the capacitor connected to pin tmr. uv has a weak 400k pull-up to v cc and may be pulled above v cc using an external pull-up. leave pin open if unused. v cc : supply voltage. bypass this pin to gnd with a 0.1f (or greater) capacitor. v cc operating range is 2.25v to 5.5v. vh1, vh2: voltage high inputs 1 and 2. when the voltage on either pin is below 0.5v, an undervoltage condition is triggered. tie pin to v cc if unused. vl1, vl2: voltage low inputs 1 and 2. when the voltage on either pin is above 0.5v, an overvoltage condition is triggered. tie pin to gnd if unused. v ptat : proportional to absolute temperature voltage output. the voltage on this pin is proportional to the selected sensors absolute temperature. an internal or external sensor is chosen with the ds pin. v ptat can drive up to 200a of load current and up to 1000pf of capacitive load. for larger load capacitances insert a 1k
ltc2995 8 2995f resistor between v ptat and the load to ensure stability. v ptat is pulled low when the supply voltage goes below the under voltage lockout threshold. v ref : voltage reference output. v ref provides a 1.8v reference voltage. v ref can drive up to 200a of load current and up to 1000pf of capacitive load. for larger load capacitances insert 1k between v ref and the load to ensure stability. leave v ref open if unused. vt1: temperature threshold 1. when v ptat crosses the voltage on vt1 with a polarity set by the ps pin, to1 is pulled low. tie vt1 to gnd if unused. vt2: temperature threshold 2. when v ptat crosses the voltage on vt2 with a polarity set by the ps pin, to2 is pulled low. tie vt2 to v cc if unused. pin functions block diagram 2995 bd vh1 ch1 ch2 cl2 ct2 ct1 cl1 uvlo 2v v cc vl1 vh2 vl2 vt2 v ref vt1 v ptat 20 1 2 3 C + C + C + C + C + C + C + C + 1.3m 500k 0.5v 200k 200k 1.2v 1.8v 400k uvlo 11 4 5 8 18 7 d C d + ds ps gnd 6 19 t to v converter to1/to2 pulse generator uv pulse generator oscillator uv v cc 400k tmr ov v cc 400k to2 v cc 400k to1 v cc 400k ov pulse generator 3 state decode 17 3 state decode 12 13 14 15 16 v cc 9 1
ltc2995 9 2995f operation overview the ltc2995 combines the functionality of a temperature measurement and monitor device with a dual voltage supervisor. it provides a buffered voltage proportional to the absolute temperature of either an internal or a remote diode (v ptat ) and compares this voltage to thresholds that can be set by external resistor dividers from the on-board reference (v ref ). the ltc2995 also provides four voltage threshold inputs that are continuously compared to an internal 0.5v reference allowing two systems voltages to be monitored for undervoltage and overvoltage conditions. diode temperature sensor temperature measurements are conducted by measuring the voltage of either an internal or an external diode with multiple test currents. the relationship between diode voltage v d and diode current i d can be solved for absolute temperature in degrees kelvin t: ? ? ? ? ? ? t = q t k t v d ln i d i s where i s is a process dependent factor on the order of 10 C13 a, is the diode ideality factor, k is the boltzmann constant and q is the electron charge. this equation shows a relationship between temperature and voltage dependent on the process depended variable i s . measuring the same diode (with the same value i s ) at two different currents (i d1 and i d2 ) yields an expression independent of i s : ln i d2 i d1 ? ? ? ? ? ? t = q t k t v d2 Cv d1 series resistance cancellation resistance in series with the remote diode causes a positive temperature error by increasing the measured voltage at each test current. the composite voltage equals: ? ? ? ? ? ? v d + v error = kt q t ln i d i s + r s t i d the ltc2995 removes this error term from the sensor signal by subtracting a cancellation voltage v cancel . a resistance extraction circuit uses one additional current measurement to determine the series resistance in the measurement path. once the correct value of the resistor is determined, v cancel equals v error . now the temperature to voltage converter input signal is free from errors due to series resistance. ltc2995 can cancel series resistances up several hundred ohms (see typical performance characteristics curves). higher series resistances cause the cancelation voltage to saturate.
ltc2995 10 2995f temperature measurements the ltc2995 continuously measures the sensor diode at different test currents and generates a voltage proportional to the absolute temperature of the sensor at the v ptat pin. the voltage at v ptat is updated every 3.5ms. the gain of v ptat is calibrated to 4mv/k for the measure- ment of the internal diode as well as for remote diodes with an ideality factor of 1.004. t kelvin = v ptat 4mv /k ( = 1.004) if an external sensor with an ideality factor different from 1.004 is used, the gain of v ptat will be scaled by the ratio of the actual ideality factor ( act ) to 1.004. in these cases, the temperature of the external sensor can be calculated from v pat by: t kelvin = v ptat 4mv / k ? 1.004 act temperature in degrees celsius can be deduced from degrees kelvin by: t celsius = t kelvin C 273.15 the three-state diode select pin (ds) determines whether the temperature of the external or the internal diode is measured and displayed at v ptat as described in table 1. table 1. diode selection diode location ds pin internal v cc external gnd both open if the ds pin is left open, the ltc2995 measures both diodes alternately and v ptat changes every 30ms from the voltage corresponding to the temperature of the internal sensor to the voltage corresponding to the temperature of the external sensor. if d + is tied to v cc , the ltc2995 measures the internal diode regardless of the state of the ds pin. applications information choosing an external sensor the ltc2995 is factory calibrated for an ideality factor of 1.004, which is typical of the popular mmbt3904 npn transistor. semiconductor purity and wafer level process- ing intrinsically limit device-to-device variation, making these devices interchangeable between manufacturers with a temperature error of typically less than 0.5c. some recommended sources are listed in table 2: table 2 recommended transistors for use as temperature sensors manufacturer part number package fairchild semiconductor mmbt3904 sot-23 central semiconductor cmbt3904 sot-23 diodes inc. mmbt3904 sot-23 on semiconductor mm bt3904lt1 sot-23 nxp mmbt3904 sot-23 infineon mmbt3904 sot-23 rohm umt3904 sc-70 discrete two terminal diodes are not recommended as remote sensing devices as their ideality factor is typically much higher than 1.004. also mos transistors are not suitable as they dont exhibit the required current to tem- perature relationship. furthermore gold doped transistors (low beta), high frequency and high voltage transistors should be avoided as remote sensing devices. connecting an external sensor the change in sensor voltage per c is hundreds of microvolts, so electrical noise must be kept to a mini- mum. bypass d + and d C with a 470pf capacitor close to the ltc2995 to suppress external noise. recommended shielding and pcb trace considerations for best noise immunity are illustrated in figure 1. figure 1. recommended pcb layout d + d C ltc2995 2995 f01 gnd 470pf gnd shield trace npn sensor
ltc2995 11 2995f d + d C 470pf ltc2995 2n3904 2995 f02 gnd applications information leakage currents at d + affect the precision of the remote temperature measurements. 100na leakage current leads to an additional error of 2c (see typical performance characteristics). note that bypass capacitors greater than 1nf will cause settling time errors in the different measurement cur- rents and therefore introduce an error in the temperature measurement (see typical performance characteristics). the ltc2995 compensates series resistance in the measurement path and thereby allows accurate remote temperature measurements even with several meters of distance between the sensor and the device. the cable length between the sensor and the ltc2995 is only limited by the mutual capacitance introduced between d + and d C which degrades measurement accuracy (see typical performance characteristics). for example an at6 cable with 50pf/m should be kept shorter than ~20m to keep the capacitance less than 1nf. to save wiring, the cathode of the remote sensor can also be connected to remote gnd and d C to local gnd as shown below. components. noise around odd multiples of 6khz (20%)is amplified by the measurement algorithm and converted at a dc offset in the temperature measurement (see typical performance characteristics). the ltc2995 can withstand up to 4kv of electrostatic discharge (esd, human body). esd beyond this voltage can damage or degrade the device including lowering the remote sensor measurement accuracy due to increased leakage currents on d + or d C . to protect the sensing inputs against larger esd strikes, external protection can be added using tvs diodes to ground (figure 3). care must be taken to choose diodes with low capacitance and low leakage currents in order not to degrade the external sensor measurement accuracy (see typical performance characteristics curves). the temperature measurement of the ltc2995 relies only on differences between the diode voltage at multiple test circuits. therefore dc offsets smaller than 300mv between remote and local gnd do not impact the precision of the temperature measurement. the cathode of the sensor can accommodate modest ground shifts across a system which is beneficial in applications where a good thermal connectivity of the sensor to a device whose temperature is to be monitored (shunt resistor, coil, etc.) is required. care must be taken if the potential difference between the cathode and d C does not only content dc but also ac figure 2. single wire remote temperature sensing figure 3. increasing esd robustness with tvs diodes to make the connection of the cable to the ic polarity insensitive during installation, two sensor transistors with opposite polarity at the end of a two wire cable can be used as shown on figure 4. again, care must be taken that the leakage current of the second transistor does not degrade the measurement accuracy. figure 4. polarity insensitive remote diode sensor d + d C 220pf 10 ltc2995 mmbt3904 pesd5z6.0 2995 f03 gnd 10 d + d C ltc2995 mmbt3904 470pf 2995 f04 gnd
ltc2995 12 2995f applications information output noise filtering the v ptat output typically exhibits 0.6mv rms (0.25c rms) noise. for applications which require lower noise digital or analog averaging can be applied to the output. choose the averaging time according to: 2 ? ? ? ? ? ? t avg = 0.01 [] chz t noise where t avg is the averaging time and t noise the desired temperature noise in c rms. for example, if the desired noise performance is 0.015c rms, set the averaging time to one second. see typical performance characteristics. temperature monitoring the ltc2995 continuously compares the voltage at v ptat to the voltages at the pins vt1 and vt2 to detect either an overtemperature (ot) or undertemperature (ut) condition. the vt1 comparator output drives the open-drain logic output pin to1 and the vt2 comparator output drives the open-drain logic output pin to2 . the polarity of these comparisons is configured via the three-state polarity select pin (ps) (table 3). table 3. temperature polarity selection ps pin function condition output v cc vt1 undertemperature threshold v ptat < vt1 to1 pulled low vt2 overtemperature threshold v ptat > vt2 to2 pulled low open vt1 overtemperature threshold v ptat > vt1 to1 pulled low vt2 overtemperature threshold v ptat > vt2 to2 pulled low gnd vt1 undertemperature threshold v ptat < vt1 to1 pulled low vt2 undertemperature threshold v ptat < vt2 to2 pulled low if pin ps is connected to v cc , the voltage on vt1 becomes an undertemperature threshold and the voltage on vt2 an overtemperature threshold. in this configuration to1 is pulled low if the voltage v ptat falls during five consecutive conversions below the undertemperature threshold vt1. once pulled low, to1 is released high again if v ptat rises above vt1 plus an additional hysteresis of about 20mv. accordingly, t02 is pulled low if the voltage v ptat rises above the overtemperature threshold vt2 and Conce pulled lowC to2 is released high if v ptat falls below vt2 minus an additional hysteresis of about 20mv. leaving ps uncon- nected configures both vt1 and vt2 as overtemperature thresholds and connecting ps to gnd configures them both as undertemperature thresholds. if the internal and external sensors are monitored alternately by leaving ds unconnected, vt1 becomes a dedicated threshold for the internal sensor and vt2 becomes a dedicated threshold for the external sensor. temperature monitor design example the ltc2995 can be configured to give an early warning if the temperature of the internal sensor rises above 60c and an alarm if the temperature passes 90c. tie the ds pin to v cc to select the internal sensor and leave the pin ps unconnected to configure both input voltages vt1 and vt2 as overtemperature thresholds. the voltages at vt1 and vt2 are set to: vt1 = (60k + 273.15k) ? 4 mv k = 1.332v vt2 = (90k + 273.15k) ? 4 mv k = 1.452v when v ptat reaches the threshold voltage on pin vt1, to1 is pulled low indicating an overtemperature early warning. if the temperature reaches 90c to2 is also pulled low, indicating an overtemperature alarm. once the temperature drops below each threshold, the corresponding to pins will return high after a time-out- period (t uoto ) set by the capacitor connected to tmr.
ltc2995 13 2995f d + ds d C 1.2v 200k 400k 1.8v v cc v ref r tc vt2 vt1 v cc v ptat ps to2 to1 3.3v ltc2995 2995 f06 ot alarm ot warning r tb r ta gnd C + C + C + to1/to2 pulse generator uvlo v cc 400k v cc 400k t/v figure 5. temperature thresholds figure 6. monitoring internal temperature with two overtemperature thresholds applications information temperature thresholds the threshold voltages at vt1 and vt2 can be set with the 1.8v reference voltage (v ref ) and a resistive divider as shown in figure 5. the following design procedure can be used to size the resistive divider. 1. calculate threshold voltages: vt1 = t1 ? 4 mv k ? act 1.004 vt2 = t2 ? 4 mv k ? act 1.004 where act denotes the ac tual ide ali t y f ac tor if an ex ternal sensor is used and t1 and t2 are the desired threshold temperatures in degrees kelvin. 2. choose r ta to obtain the desired vt1 threshold for a desired current through the resistive divider (i ref ): r ta = vt1 i ref 3. choose r tb to obtain the desired vt2 threshold: r tb = vt2 C vt1 i ref 2995 f05 v ptat r tc r tb r ta v ref = 1.8v 1.8v slope = t act o t 200k t 1 t 2 l vt2 vt1 o.8v k mv
ltc2995 14 2995f applications information 4. finally r tc is determined by: r tc = 1.8v C vt2 i ref in the temperature monitor example discussed earlier with thresholds at vt1 = 60c and vt2 = 90c and a desired reference current of 10a, the required values for r ta , r tb and r tc can be calculated as: r ta = 1.332v 10a = 133.2k r tb = 1.452v C 1.332v 10a = 12k r tc = 1.8v C 1.452v 10a = 34.8k voltage monitoring in addition to temperature measurement, the ltc2995 features a low power dual voltage monitoring circuit. each voltage monitor has two inputs (vh1/vl1 and vh2/vl2) for detecting undervoltage and overvoltage conditions. if either vh1 or vh2 falls below 0.5v (typical), the ltc2995 communicates an undervoltage condition by pulling uv low. similar, an overvoltage condition is flagged by pulling ov low if either vl1 or vl2 rises above 0.5v. when configured to monitor a positive voltage vn using the 3-resistor circuit configuration shown in figure 5, v hn will be connected to the high side tap of the resistive divider and v ln will be connected to the low side tap of the resistive divider. voltage monitor design procedure the following 3-step design procedure selects appropriate resistances to obtain the desired uv and ov trip points for the voltage monitor circuit in figure 7. for supply monitoring, v n is the desired nominal operat- ing voltage, i n is the desired nominal current through the resistive divider, v ov is the desired overvoltage trip point, and v uv is the desired undervoltage trip point. 1. r a is chosen to set the desired trip point for the overvoltage monitor: r a = 0.5v i n ? v n v ov (1) 2. once r a is known, r b is chosen to set the desired trip point for the undervoltage monitor: r b = 0.5v i n ? v n v uv Cr a (2) 3. once, r a and r b are known, r c is determined by: r c = v n i n Cr a Cr b (3) voltage monitor example a typical voltage monitor application is shown in figure 2. the monitored voltage is a 5v 10% supply. nominal current in the resistive divider is 10a. 1. find r a to set the ov trip point of the monitor: r a = 0.5v 10a ? 5v 5.5v 45.3k figure 7. 3-resistor positive uv/ov monitoring C + C + + C 0.5v ltc2995 uv n v hn r c r b r a 2995 f07 v n v ln ov n
ltc2995 15 2995f applications information 2. find r b to set the uv trip point of the monitor: r b = 0.5v 10a ? 5v 4.5v C 453 ? 10k 3. determine r c to complete the design: r c = 5v 10a C453 C 100 ? 442k power-up and undervoltage lockout as soon as v cc reaches approximately 1v during power-up, the ov as well as to1 and to2 w e a k l y p u l l t o v cc while the uv output asserts low indicating an undervolt- age lockout condition. above v cc = 2v (typical), the vh and vl inputs take control. once both vh inputs and v cc are valid, an internal timer is started. after an adjustable delay time, uv weakly pulls high. when v cc falls below 1.9v, the ltc2995 indicates again an undervoltage lockout (uvl o) condition by pulling low uv while ov is cleared. threshold accuracy reset threshold accuracy is important in a supply sensitive system. ideally, such a system would only reset if supply voltages fell outside the exact threshold for a specified margin. all ltc2995 vhn/vln inputs have a relative threshold accuracy of 1.5% over the full operating temperature range. for example, when the ltc2995 is configured to monitor a 5v input with a 10% tolerance, the desired uv trip point is 4.5v. because of the 1.5% relative accuracy of the ltc2995, the uv trip point can be anywhere between 4.433v and 4.567v which is 4.5v 1.5%. likewise, the accuracy of the resistances chosen for r a , r b , and r c can affect the uv and ov trip points as well. using the previous example, if the resistances used to set the uv trip point have 1% accuracy, the uv trip range can grow to between 4.354v and 4.650v. this is illustrated in the following calculations. the uv trip point is given as: v uv = 0.5v t 1 + r c r a + r b ? ? ? ? ? ? the two extreme conditions, with a relative accuracy of 1.5% and resistance accuracy of 1%, result in: v uv(min) = 0.5v t 0.985 t 1 + r c t 0.99 (r a + r b ) t 1.01 ? ? ? ? ? ? and v uv(max) = 0.5v t 1.015 t 1 + r c t 1.01 (r a + r b ) t 0.99 ? ? ? ? ? ? for a desired trip point of 4.5v, r c r a + r b = 8 therefore, v uv(min) = 0.5v t 0.985 t 1 + 8 0.99 1.01 = 4.3545v ? ? ? ? ? ? and v uv(max) = 0.5v t 1.015 t 1 + 8 1.01 0.99 = 4.650v ? ? ? ? ? ? glitch immunity in any supervisory application, noise on the monitored dc voltage can cause spurious resets. to solve this problem without adding hysteresis to the vh/vl comparators, which would add error to the trip voltage, the ltc2995 lowpass filters the output of the comparator. this filter causes the output of the comparator to be integrated before assert- ing the uv or ov logic. any transient at the input of the comparator must be of suf ficient magnitude and duration before the comparator will trigger the output logic. the typical performance characteristics section shows a graph of the typical transient duration vs comparator overdrive. in temperature monitoring, the voltage at v ptat must exceed a threshold for five consecutive temperature up- date intervals before the respective to pin is pulled low. once the v ptat voltage crosses back the threshold with an additional 20mv of hysteresis, the respective to pin is released after a single update interval and an additional delay adjustable by the capacitor on tmr.
ltc2995 16 2995f timing of alert outputs the ltc2995 has an adjustable timeout period (t uoto ) that holds uv , ov , to1 or to2 asserted after any faults have cleared. this delay will minimize the effect of input noise with a frequency above 1/t uoto . a voltage monitoring example: when any vh drops below its threshold, the uv pin asserts low. when all vh inputs recover above their thresholds, the output timer starts. if all inputs remain above their thresholds when the timer finishes, the uv pin weakly pulls high. however, if any input falls below its threshold during this timeout period, the timer resets and restarts when all inputs are again above the thresholds. a temperature monitoring example: tying ps to v cc configures to2 as overtemperature output. in case of an overtemperature condition pin to2 asserts low. the output timer starts when the temperature crosses back below the threshold minus the temperature hysteresis if the temperature remains below the threshold, the timer finishes and pin to2 releases high. selecting the timing capacitor the timeout period (t uoto ) for the ltc2995 is adjustable in order to accommodate a variety of applications. connect- ing a capacitor, c tmr , between the tmr pin and ground sets the timeout period. the value of capacitor needed for a particular timeout period is: c tmr = t uoto C0.5ms 8[ms / nf] the reset timeout period vs capacitance graph found in the typical performance characteristics section shows the desired delay time as a function of the value of the timer capacitor that should be used. leaving the tmr pin open with no external capacitor generates a timeout period of approximately 500s. for long timeout periods, the only limitation is the availability of a large value capacitor with low leakage. capacitor leakage current must not exceed the minimum tmr charging current of 1.5a. tying the tmr pin to v cc will bypass the timeout period and no delay will occur. digital output characteristics the dc characteristics of the uv , ov , to1 and to2 pull-up and pull-down strength are shown in the typical perfor- mance characteristics section. each pin has a weak 400k internal pull-up to v cc and a strong pull-down to ground and can be pulled above v cc . this arrangement allows these pins to have open-drain behavior while possessing several other beneficial char- acteristics. the weak pull-up eliminates the need for an external pull-up resistor when the rise time on the pin is not critical. on the other hand, the open drain configuration allows for wired-or connections and can be useful when more than one signal needs to pull-down on the output. at v cc = 1v, the weak pull-up current is barely turned on. therefore, an external pull-up resistor of no more than 100k is recommended on the pin if the state and pull-up strength of the pin is crucial at very low v cc . note however, by adding an external pull-up resistor, the pull-up strength on the pin is increased. therefore, if it is connected in a wired-or connection, the pull-down strength of any single device needs to accommodate this additional pull-up strength. output rise and fall time estimation the uv , ov , to1 and to2 outputs have strong pull-down capability. the following formula estimates the output fall time (90% to 10%) for a particular external load capaci- tance (c load ): t fall 2.2 ? r pd ? c load where r pd is the on-resistance of the internal pull-down transistor estimated to be typically 40 at v dd > 1v and at room temperature (25c), and c load is the external load capacitance on the pin. assuming a 150pf load capacitance, the fall time is about 13ns. the rise time on the uv , ov , to1 and to2 pins is limited by a 400k pull-up resistance to v dd . a similar formula estimates the output rise time (10% to 90%): t rise 2.2 ? r pu ? c load where r pu is the pull-up resistance. applications information
ltc2995 17 2995f 10% voltage monitor (1.8v and 2.5v) and internal/remote overtemperature monitor typical applications 20% voltage monitor (12v and 5v) and 0c to 70c internal ut/ot monitoring with common temperature and powergood led power supplies temperature and power good led vh1 vl1 vh2 vl2 d + d C ltc2995 442k 113k 12v 5v 41.2k 2995 ta03 vt1 vt2 43k 28k 110k ot t > 70c ut t < 0c +20% C20% gnd tmr v ref 4.12k 2.15k 21.5k v ptat to2 to1 ov uv v cc ps ds 0.1f 2.15k vh1 vl1 vh2 vl2 d + d C ltc2995 194k 124k 2.5v 1.8v 45.3k 2995 ta02 vt1 vt2 20k 20k 140k ot t > 125c for external sensor mmbt390 ot t > 75c for internal sensor +10% C10% gnd tmr v ref 45.3k 10.2k 10.2k v ptat to2 to1 ov uv v cc ps ds 5nf 470pf 0.1f power supplies
ltc2995 18 2995f typical applications celsius thermometer and 10% voltage monitor (1.8v and 2.5v) 10% voltage monitor (12v and 5v) and C20c to 70c internal ut/ot monitor with manual undervoltage reset button power supplies vh1 vl1 vh2 vl2 d + d C ltc2995 44.2k 115k 12v 5v 4.53k vt1 vt2 43k 36k 102k ot t > 70c ut t < C20c +10% C10% gnd tmr v ref 4.53k 1k manual reset button (normally open) 1k v ptat to2 to1 ov uv v cc ps ds 0.1f system reset 2995 ta05 power supplies vh1 vl1 vh2 vl2 d + d C ltc2995 194k 124k 2.5v 1.8v 45.3k 2995 ta04 vt1 vt2 +10% C10% 1.8v 100k 1k 4mv/k gnd tmr to2 to1 45.3k 10.2k 10.2k v ptat ov uv v cc ps ds 0.1f 5nf 470pf mmbt3904 v ref C + 62k 143k 1f 0.1f ltc1150 5v C5v 10mv/c 0v at 0c 150k 1.8k
ltc2995 19 2995f information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- t i o n t h a t t h e i n t e r c o n n e c t i o n o f i t s c i r c u i t s a s d e s c r i b e d h e r e i n w i l l n o t i n f r i n g e o n e x i s t i n g p a t e n t r i g h t s . package description 3.00 0.10 (4 sides) recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 1.65 0.05 note: 1. drawing is not a jedec package outline 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.40 0.10 bottom view?xposed pad 1.65 0.10 (4-sides) 0.75 0.05 r = 0.115 typ r = 0.05 typ 0.20 0.05 1 pin 1 notch r = 0.20 typ or 0.25 45 chamfer 19 20 2 0.40 bsc 0.200 ref 2.10 0.05 3.50 0.05 (4 sides) 0.70 0.05 0.00 ?0.05 (ud20) qfn 0306 rev a 0.20 0.05 0.40 bsc package outline ud package 20-lead plastic qfn (3mm 3mm) (reference ltc dwg # 05-08-1720 rev a) please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
ltc2995 20 2995f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2012 lt 0412 ? printed in usa related parts typical application part number description comments ltc2990 remote/internal temperature, voltage, current monitor i 2 c interface ltc2991 remote/internal temperature sensor i 2 c interface, eight single-ended inputs ltc2997 remote/internal temperature sensor analog v ptat output voltage ltc2900 programmable quad supply monitor adjustable reset , 10-lead msop and 3mm 3mm 10-lead dfn ltc2901 programmable quad supply monitor adjustable reset and watchdog timer, 16-lead ssop package ltc2902 programmable quad supply monitor adjustable reset and tolerance, 16-lead ssop package, margining functions ltc2903 precision quad supply monitor 6-lead sot-23 package, ultralow voltage reset ltc2904 3-state programmable precision dual supply monitor adjustable tolerance, 8-lead sot-23 package ltc2905 3-state programmable precision dual supply monitor adjustable reset and tolerance, 8-lead sot-23 package ltc2906 precision dual supply monitor 1-selectable and one adjustable separate v cc pin, rst/ rst outputs ltc2907 precision dual supply monitor 1-selectable and one adjustable separate v cc , adjustable reset timer ltc2908 precision six supply monitor (four fixed and two adjustable) 8-lead sot-23 and ddb packages ltc2909 prevision dual input uv, ov and negative voltage monitor 2 adj inputs, monitors negative voltages ltc2912 single uv/ov positive voltage monitor separate v cc pin, 8-lead tsot and 3mm 2mm dfn packages ltc2913 dual uv/ov positive voltage monitor separate v cc pin, 10-lead msop and 3mm 3mm dfn packages LTC2914 quad uv/ov positive/negative voltage monitor separate v cc pin, 16-lead ssop and 5mm 2mm dfn packages dual ov/uv 10% supply and 75c/125c ot/ot remote temperature monitor asic/ cpu/ fpga vh1 vl1 vh2 vl2 d + d C ltc2995 194k 64.4k 2.5v 1.2v 45.3k 2995 ta06 vt1 vt2 v ref +10% C10% gnd tmr 45.3k 10.2k 10.2k v ptat to2 to1 ov uv v cc ps ds 0.1f 5nf 140k 20k 20k 470pf ot t > 125c ot t > 75c a/d

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