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rev. c information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. a tmp35/tmp36/tmp37 one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 www.analog.com fax: 781/326-8703 ?analog devices, inc., 2002 low voltage temperature sensors functional block diagram +v s (2.7v to 5.5v) v out shutdown tmp35/ tmp36/ tmp37 package types available rt-5 (sot-23) 1 2 3 5 4 top view (not to scale) nc = no connect v out shutdown gnd nc +v s rn-8 (soic) 1 2 3 4 8 7 6 5 top view (not to scale) nc = no connect v out shutdown nc nc +v s nc nc gnd to-92 1 3 2 bottom view (not to scale) pin 1, +v s ; pin 2, v out ; pin 3, gnd features low voltage operation (2.7 v to 5.5 v) calibrated directly in c 10 mv/ c scale factor (20 mv/ c on tmp37) 2 c accuracy over temperature (typ) 0.5 c linearity (typ) stable with large capacitive loads specified ?0 c to +125 c, operation to +150 c less than 50 a quiescent current shutdown current 0.5 a max low self-heating applications environmental control systems thermal protection industrial process control fire alarms power system monitors cpu thermal management product description the tmp35, tmp36, and tmp37 are low voltage, precision centigrade temperature sensors. they provide a voltage output that is linearly proportional to the celsius (centigrade) tem- perature. the tmp35/tmp36/tmp37 do not require any external calibration to provide typical accuracies of 1 c at +25 c and 2 c over the ?0 c to +125 c temperature range. the low output impedance of the tmp35/tmp36/tmp37 and its linear output and precise calibration simplify interfacing to temperature control circuitry and a/d converters. all three devices are intended for single-supply operation from 2.7 v to 5.5 v maximum. supply current runs well below 50 a, provid ing very low self-heating?ess than 0.1 c in still air. in addi tion, a shutdown function is provided to cut supply current to less than 0.5 a. the tmp35 is functionally compatible with the lm35/lm45 and provides a 250 mv output at 25 c. the tmp35 reads tempera tures from 10 c to 125 c. the tmp36 is specified from ?0 c to +125 c, provides a 750 mv output at 25 c, and operates to +125 c from a single 2.7 v supply. the tmp36 is functionally compatible with the lm50. both the tmp35 and tmp36 have an output scale factor of 10 mv/ c. the tmp37 is intended for applications over the range 5 c to 100 c and provides an output scale factor of 20 mv/ c. the tmp37 provides a 500 mv output at 25 c. operation extends to 150 c with reduced accuracy for all devices when operating from a 5 v supply. the tmp35/tmp36/tmp37 are all available in low cost 3-lead to-92, soic-8, and 5-lead sot-23 surface-mount packages.
rev. c ? tmp35/tmp36/tmp37?pecifications 1 (v s = 2.7 v to 5.5 v, ?0 c t a +125 c, unless otherwise noted.) parameter symbol conditions min typ max unit accuracy tmp35/tmp36/tmp37f t a = 25 c 1 2 c tmp35/tmp36/tmp37g t a = 25 c 1 3 c tmp35/tmp36/tmp37f over rated temperature 2 3 c tmp35/tmp36/tmp37g over rated temperature 2 4 c scale factor, tmp35 10 c t a 125 c1 09 .8/10.2 mv/ c scale factor, tmp36 ?0 c t a + 125 c1 09 .8/10.2 mv/ c scale factor, tmp37 5 c t a 85 c2 0 19.6/20.4 mv/ c 5 c t a 100 c2 0 19.6/20.4 mv/ c 3.0 v +v s 5.5 v load regulation 0 a i l 50 a ?0 c t a + 105 c620m c/ a ?05 c t a +125 c2560m c/ a power supply rejection ratio psrr t a = 25 c30 100 m c/v 3.0 v +v s 5.5 v 50 m c/v linearity 0.5 c long-term stability t a = 150 c for 1 khrs 0.4 c shutdown logic high input voltage v ih v s = 2.7 v 1.8 v logic low input voltage v il v s = 5.5 v 400 mv output tmp35 output voltage t a = 25 c 250 mv tmp36 output voltage t a = 25 c 750 mv tmp37 output voltage t a = 25 c 500 mv output voltage range 100 2000 mv output load current i l 050 a short-circuit current i sc note 2 250 a capacitive load driving c l no oscillations 2 1000 10000 pf device turn-on time output within 1 c 0.5 1 ms 100 k ? 100 pf load 2 power supply supply range +v s 2.7 5.5 v supply current i sy (on) unloaded 50 a supply current (shutdown) i sy (off) unloaded 0.01 0.5 a notes 1 does not consider errors caused by self-heating. 2 guaranteed but not tested. specifications subject to change without notice. temperature ? c ?0 load reg ?m c/ a 050 100 150 50 30 20 10 0 40 figure 1. load reg vs. temperature (m c/ a)
rev. c tmp35/tmp36/tmp37 ? absolute maximum ratings 1, 2, 3 supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 v shutdown pin . . . . . . . . . . . . . . gnd shutdown +v s output pin . . . . . . . . . . . . . . . . . . . . . . gnd v out +v s operating temperature range . . . . . . . . . . ?5 c to +150 c dice junction temperature . . . . . . . . . . . . . . . . . . . . . . 175 c storage temperature range . . . . . . . . . . . . ?5 c to +160 c lead temperature (soldering, 60 sec) . . . . . . . . . . . . . 300 c notes 1 stresses above those listed under absolute maximum ratings may cause perma- nent damage to the device. this is a stress rating only; functional operation at or above this specification is not implied. exposure to maximum rating conditions for extended periods may affect device reliability. 2 digital inputs are protected; however, permanent damage may occur on unpro- tected units from high energy electrostatic fields. keep units in conductive foam or packaging at all times until ready to use. use proper antistatic handling procedures. 3 remove power before inserting or removing units from their sockets. package type ja jc unit to-92 (t9 suffix) 162 120 c/w soic-8 (s suffix) 158 43 c/w sot-23 (rt suffix) 300 180 c/w ja is specified for device in socket (worst-case conditions). ordering guide accuracy linear at 25 c operating package model ( c max) temperature range options 1 tmp35ft9 2.0 10 c to 125 c to-92 tmp35gt9 3.0 10 c to 125 c to-92 tmp35fs 2.0 10 c to 125 c rn-8 tmp35gs 3.0 10 c to 125 c rn-8 tmp35grt 2 3.0 10 c to 125 c rt-5 tmp36ft9 2.0 ?0 c to +125 c to-92 tmp36gt9 3.0 ?0 c to +125 c to-92 tmp36fs 2.0 ?0 c to +125 c rn-8 tmp36gs 3.0 ?0 c to +125 c rn-8 tmp36grt 2 3.0 ?0 c to +125 c rt-5 tmp37ft9 2.0 5 c to 100 c to-92 tmp37gt9 3.0 5 c to 100 c to-92 tmp37fs 2.0 5 c to 100 c rn-8 tmp37gs 3.0 5 c to 100 c rn-8 tmp37grt 2 3.0 5 c to 100 c rt-5 notes 1 soic = small outline integrated circuit; rt = plastic surface mount; to = plastic. 2 consult factory for availability. functional description an equivalent circuit for the tmp3x family of micropower, centigrade temperature sensors is shown in figure 2. at the heart of the temperature sensor is a band gap core, which is comprised of transistors q1 and q2, biased by q3 to approxi- mately 8 a. the band gap core operates both q1 and q2 at the same collector current level; however, since the emitter area of q1 is 10 times that of q2, q1? v be and q2? v be are not equal by the following relationship: ? v be = v t ln a e,q 1 a e,q 2 ? ? ? ? ? ? shdn +v out +v s 3x 25 a 2x q2 1x r1 r2 r3 7.5 a q3 2x gnd q4 q1 10x 6x figure 2. temperature sensor simplified equivalent circuit resistors r1 and r2 are used to scale this result to produce the output voltage transfer characteristic of each temperature sensor and, simultaneously, r2 and r3 are used to scale q1? v be as an offset term in v out . table i summarizes the differences between the three temperature sensors?output characteristics. table i. tmp3x output characteristics offset output voltage output voltage sensor voltage (v) scaling (mv/ c) @ 25 c (mv) tmp35 0 10 250 tmp36 0.5 10 750 tmp37 0 20 500 the output voltage of the temperature sensor is available at the emitter of q4, which buffers the band gap core and provides load current drive. q4? current gain, working with the available base current drive from the previous stage, sets the short-circuit current limit of these devices to 250 a. caution esd (electrostatic discharge) sensitive device. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although the tmp35/tmp36/tmp37 features proprietary esd protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality. warning! esd sensitive device
rev. c tmp35/tmp36/tmp37 ? temperature ? c 1.4 0 1.2 1.0 0.8 0.6 0.4 0.2 1.6 1.8 2.0 50 25 0 25 50 75 100 125 output voltage ?v a b c a. tmp35 b. tmp36 c. tmp37 v s = 3v tpc 1. output voltage vs. temperature a. maximum limit (g grade) b. typical accuracy error c. minimum limit (g grade) temperature ? c 2 5 1 0 1 2 3 4 3 4 5 02040608 0 100 120 140 a b c accuracy error ? c tpc 2. accuracy error vs. temperature temperature ? c 0.4 0.3 0 50 125 25 0 25 50 75 100 0.2 0.1 power supply rejection ? c/v v+ = 3v to 5.5v, no load tpc 3. power supply rejection vs. temperature frequency ?hz 100 0.01 20 100k 100 1k 10k 31.6 10 3.16 1 0.32 0.1 0.032 power supply rejection ? c/v tpc 4. power supply rejection vs. frequency temperature ? c 4 3 0 2 1 5 50 125 25 0 25 50 75 100 minimum supply voltage ?v b a minimum supply voltage required to meet data sheet specification no load a. tmp35/tmp36 b. tmp37 tpc 5. minimum supply voltage vs. temperature supply current ? a temperature ? c 50 40 10 30 20 60 50 125 25 0 25 50 75 100 no load b a a. v+ = 5v b. v+ = 3v tpc 6. supply current vs. temperature ?typical performance characteristics
rev. c tmp35/tmp36/tmp37 ? supply voltage ?v 40 30 0 20 10 50 07 123456 supply current ? a t a = 25?, no load 8 tpc 7. supply current vs. supply voltage temperature ? c 40 30 0 20 10 50 50 125 25 0 25 50 75 100 a. v+ = 5v b. v+ = 3v no load a b supply current ?na tpc 8. s upply current vs. temperature (shutdown = 0 v) temperature ? c 400 300 0 200 100 50 125 25 0 25 50 75 100 = v+ and shutdown pins low to high (0v to 3v) v out settles within ?? = v+ and shutdown pins high to low (3v to 0v) response time ? s tpc 9. v out response time for v+ power-up/power- down vs. temperature temperature ? c 400 300 0 200 100 50 125 25 0 25 50 75 100 = shutdown pin high to low (3v to 0v) = shutdown pin low to high (0v to 3v) v out settles within ?? response time ? s tpc 10. v out response time for shutdown pin vs. temperature time ?? 0 1.0 0.8 0.6 0.4 0.2 50 250 0 100 50 150 200 300 350 400 450 output voltage ?v 0 1.0 0.8 0.6 0.4 0.2 v+ = 3v shutdown = signal t a = 25 c v+ and shutdown = t a = 25 c signal tpc 11. v out response time to shutdown and v+ pins vs. time time ?sec 70 0 60 50 40 30 20 10 80 90 100 110 0 100 200 300 400 500 600 a b c v in = 3v, 5v percent of change ?% a. tmp35 soic soldered to 0.5" x 0.3" cu pcb b. tmp36 soic soldered to 0.6" x 0.4" cu pcb c. tmp35 to-92 in socket soldered to 1" x 0.4" cu pcb tpc 12. thermal response time in still air
rev. c tmp35/tmp36/tmp37 ? air velocity ?fpm 0 60 40 20 80 140 100 120 0 100 200 300 400 500 600 time constant ?sec a b c a. tmp35 soic soldered to 0.5" x 0.3" cu pcb b. tmp36 soic soldered to 0.6" x 0.4" cu pc c. tmp35 to-92 in socket soldered to 1" x 0.4" cu pcb v in = 3v, 5v 700 tpc 13. thermal response time constant in forced air time ?sec 70 0 60 50 40 30 20 10 80 90 100 110 0 10 20 30 40 50 60 a b c change ?% v in = 3v, 5v a. tmp35 soic soldered to 0.5" x 0.3" cu pcb b. tmp36 soic soldered to 0.6" x 0.4" cu pcb c. tmp35 to-92 in socket soldered to 1" x 0.4" cu pcb tpc 14. thermal response time in stirred oil bath 10 0% 100 90 1ms 10mv time/division volt/division tpc 15. temperature sensor wideband output noise voltage. gain = 100, bw = 157 khz a b frequency ?hz 2400 1000 0 10 10k 100 1k 2200 2000 1600 1800 1400 1200 800 600 400 200 a. tmp35/36 b. tmp37 voltage noise density ?nv/ hz tpc 16. voltage noise spectral density vs. frequency
rev. c tmp35/tmp36/tmp37 ? applications section shutdown operation all tmp3x devices include a shutdown capability that reduces the power supply drain to less than 0.5 a maximum. this feature, available only in the soic-8 and the sot-23 packages, is ttl/ cmos level compatible, provided that the temperature sensor supply voltage is equal in magnitude to the logic supply voltage. internal to the tmp3x at the shutdown pin, a pull-up current source to v in is connected. this permits the shutdown pin to be driven from an open-collector/drain driver. a logic low, or zero-volt condition on the shutdown pin, is required to turn the output stage off. during shutdown, the output of the temperature sensors becomes a high impedance state where the potential of the output pin would then be determined by external circuitry. if the shutdown feature is not used, it is recommended that the shutdown pin be connected to v in (pin 8 on the soic-8, pin 2 on the sot-23). the shutdown response time of these temperature sensors is illustrated in tpcs 9, 10, and 11. mounting considerations if the tmp3x temperature sensors are thermally attached and protected, they can be used in any temperature measurement application where the maximum temperature range of the medium is between ?0 c to +125 c. properly cemented or glued to the surface of the medium, these sensors will be within 0.01 c of the surface temperature. caution should be exercised, especially with to-92 packages, because the leads and any wiring to the device can act as heat pipes, introducing errors if the surrounding air-surface interface is not isothermal. avoiding this condition is easily achieved by dabbing the leads of the temperature sensor and the hookup wires with a bead of thermally conductive epoxy. this will ensure that the tmp3x die temperature is not affected by the surrounding air temperature. because plastic ic packaging technology is used, excessive mechanical stress should be avoided when fastening the device with a clamp or a screw-on heat tab. t hermally conductive epoxy or glue, which must be electrically nonconductive, is recommended under typical mounting conditions. these temperature sensors, as well as any associated circuitry, should be kept insulated and dry to avoid leakage and corrosion. in wet or corrosive environments, any electrically isolated metal or ceramic well can be used to shield the temperature sensors. condensation at very cold temperatures can cause errors and should be avoided by sealing the device, using electrically non- conductive epoxy paints or dip or any one of many printed circuit board coatings and varnishes. thermal environment effects the thermal environment in which the tmp3x sensors are used determines two important characteristics: self-heating effects and thermal response time. illustrated in figure 3 is a thermal model of the tmp3x temperature sensors that is useful in understanding these characteristics. t j jc t c ca c ch c c p d t a figure 3. thermal circuit model in the to-92 package, the thermal resistance junction-to-case, jc , is 120 c/w. the thermal resistance case-to-ambient, ca , is the difference between ja and jc , and is determined by the characteristics of the thermal connection. the temperature sensor? power dissipation, represented by p d , is the product of the total voltage across the device and its total supply current (including any current delivered to the load). the rise in die temperature above the medium? ambient temperature is given by: tp t dccaa jj = + () + ? thus, the die temperature rise of a tmp35 ?t?package mounted into a socket in still air at 25 c and driven from a 5 v supply is less than 0.04 c. the transient response of the tmp3x sensors to a step change in the temperature is determined by the thermal resistances and the thermal capacities of the die, c ch , and the case, c c . the thermal capacity of the case, c c , varies with the measurement medium since it includes anything in direct contact with the package. in all practical cases, the thermal capacity of the case is the limiting factor in the thermal response time of the sensor and can be represented by a single-pole rc time constant response. tpcs 12 and 14 illustrate the thermal response time of the tmp3x sensors under various conditions. the thermal time constant of a temperature sensor is defined as the time required for the sensor to reach 63.2% of the final value for a step change in the temperature. for example, the thermal time constant of a tmp35 ??package sensor mounted onto a 0.5" by 0.3" pcb is less than 50 sec in air, whereas in a stirred oil bath, the time constant is less than 3 seconds. basic temperature sensor connections figure 4 illustrates the basic circuit configuration for the tmp3x family of temperature sensors. the table shown in the figure illustrates the pin assignments of the temperature sensors for the three package types. for the sot-23, pin 3 is labeled as ?c?as are pins 2, 3, 6, and 7 on the soic-8 package. it is recommended that no electrical connections be made to these pins. if the shutdown feature is not needed on the sot-23 or the soic-8 package, the shutdown pin should be connected to v s . 2.7v < v s < 5.5v v out tmp3x 0.1 f v s gnd package v s gnd v out shdn soic-8 8 4 1 5 sot-23-5 2 5 1 4 to-92 1 3 2 na pin assignments shdn figure 4. basic temperature sensor circuit configuration
rev. c tmp35/tmp36/tmp37 ? note the 0.1 f bypass capacitor on the input. this capacitor should be a ceramic type, have very short leads (surface mount would be preferable), and be located as close a physical proxim- ity to the temperature sensor supply pin as practical. since these temperature sensors operate on very little supply current and could be exposed to very hostile electrical environments, it is important to minimize the effects of rfi (radio frequency interference) on these devices. the effect of rfi on these temperature sensors in specific and analog ics in general is manifested as abnormal dc shifts in the output voltage due to the rectification of the high frequency ambient noise by the ic. in those cases where the devices are operated in the presence of high frequency radiated or conducted noise, a large value tanta- lum capacitor ( 2.2 f) placed across the 0.1 f ceramic may offer additional noise immunity. fahrenheit thermometers although the tmp3x temperature sensors are centigrade tem- perature sensors, a few components can be used to convert the output voltage and transfer characteristics to directly read fahr- enheit temperatures. shown in figure 5a is an example of a simple fahrenheit thermometer using either the tmp35 or the tmp37. this circuit can be used to sense temperatures from 41 f to 257 f, with an output transfer characteristic of 1 mv/ f using the tmp35 and from 41 f to 212 f using the tmp37 with an output characteristic of 2 mv/ f. this particular approach does not lend itself well to the tmp36 because of its inherent 0.5 v output offset. the circuit is constructed with an a d589, a 1.23 v voltage reference, and four resistors whose values f or each sensor are shown in the figure table. the scaling of the output resistance levels was to ensure minimum output loading on the temperature sensors. a generalized expression for the circuit? transfer equation is given by: v out = r 1 r 1 + r 2 ? ? ? ? ? ? tmp 35 () + r 3 r 3 + r 4 ? ? ? ? ? ? ad 589 () where: tmp 35 = output voltage of the tmp35, or the tmp37, at the measurement temperature, t m , and ad 589 = output voltage of the reference = 1.23 v. note that the output voltage of this circuit is not referenced to the circuit? common. if this output voltage were to be applied directly to the input of an adc, the adc? common should be adjusted accordingly. sensor tcv out r1 (k ) tmp35 1mv/ f 45.3 10 10 374 tmp37 2mv/ f 45.3 10 10 182 r2 (k )r3 (k )r4 (k ) pin assignments tmp35/37 gnd r1 r2 r3 r4 ad589 1.23v 0.1 f v out v s v out v s figure 5a. tmp35/tmp37 fahrenheit thermometers the same circuit principles can be applied to the tmp36, but because of the tmp36? inherent offset, the circuit uses two less resistors as shown in figure 5b. in this circuit, the output voltage transfer characteristic is 1 mv/ f but is referenced to the circuit? common; however, there is a 58 mv (58 f) offset in the output voltage. for example, the output voltage of the circuit would read 18 mv were the tmp36 placed in ?0 f ambient environment and 315 mv at 257 f. tmp36 gnd 0.1 f v out @ 1mv/ f ?58 f v out @ ?0 f = 18mv v out @ +257 f = 315mv v out v s r1 45.3k r2 10k v s figure 5b. tmp36 fahrenheit thermometer version 1 at the expense of additional circuitry, the offset produced by the circuit in figure 5b can be avoided by using the circuit in figure 5c. in this circuit, the output of the tmp36 is conditioned by a single- supply, micropower op amp, the op193. although the entire circuit operates from a single 3 v supply, the output voltage of the circuit reads the temperature directly, with a transfer character- istic of 1 mv/ f, without offset. this is accomplished through the use of an adm660, a supply voltage inverter. the 3 v supply is inverted and applied to the p193? v?terminal. thus, for a temperature range between ?0 f and +257 f, the output of the circuit reads ?0 mv to +257 mv. a general expression for the circuit? transfer equation is given by: v out = r 6 r 5 + r 6 ? ? ? ? ? ? 1 + r 4 r 3 ? ? ? ? ? ? tmp 36 () ? r 4 r 3 ? ? ? ? ? ? v s 2 ? ? ? ? ? ? average and differential temperature measurement in many commercial and industrial environments, temperature sensors are often used to measure the average temperature in a building, or the difference in temperature between two locations on a factory floor or in an industrial process. the circuits in figures 6a and 6b demonstrate an inexpensive approach to average and differential temperature measurement. in figure 6a, an op193 is used to sum the outputs of three temperature sensors to pr oduce an output voltage scaled by 10 mv/ c that represents the average tem perature at three loca- tions. the circuit can be extended to as many temperature sensors as required as long as the circuit? transfer equation is maintained. in this application, it is recommended that one temperature sensor type be used throughout the circuit; other- wise, the output voltage of the circuit will not produce an accurate reading of the various am bient conditions.
rev. c tmp35/tmp36/tmp37 ? the circuit in figure 6b illustrates how a pair of tmp3x sensors can be used with an op193 configured as a difference amplifier to read the difference in temperature between two locations. in th ese applications, it is always possible that one temperature sensor would be reading a temperature below that of the other sensor. to accommodate this condition, the output of the op193 is offset to a voltage at one-half the supply via r5 and r6. thus, the output voltage of the circuit is measured relative to this point, op193 0.1 f 2 3 4 1 7 v temp( avg) @ 10mv/ c for tmp35/36 @ 20mv/ c for tmp35/36 2.7v < +v s < 5.5v for r1 = r2 = r3 = r; v temp( avg) = 1 (tmp3x 1 + tmp3x 2 + tmp3x 3 ) 3 r1 300k r2 300k r3 300k tmp3x tmp3x tmp3x r4 7.5k r1 3 r4 = r6 r6 7.5k r5 100k r5 = figure 6a. configuring multiple sensors for average temperature measurements element r2 r4 r5 r6 tmp36 v out r1 50k v s adm660 tmp36 op193 r2 50k r3 r4 +3v c1 10 f r5 0.1 f 10 f ?v 10 f/0.1 f gnd nc 10 f nc r6 1 2 3 4 5 6 7 2 3 4 6 8 8 v out @ 1mv/ f ?0 f t a +257 f 258.6k 10k 47.7k 10k figure 5c. tmp36 fahrenheit thermometer version 2 as shown in the figure. using the tmp36, the output voltage of the circuit is scaled by 10 mv/ c. to minimize error in the differ- ence between the two measured temperatures, a common, readily available thin-film resistor network is used for r1?4. tmp36 @ t1 0.1 f 0.1 f 2 3 4 6 7 op193 1 f v out r3 * r4 * r2 * r1 * 2.7v < v s < 5.5v tmp36 @ t2 r5 100k r6 100k v out = t2 ?t1 @ 10mv/ c v s 2 * r1?4, caddock t914?00k?00, or equivalent 0.1 f r7 100k r8 25k r9 25k 0 t a 125 c centered at centered at figure 6b. configuring multiple sensors for differential temperature measurements
rev. c tmp35/tmp36/tmp37 ?0 microprocessor interrupt generator these inexpensive temperature sensors can be used with a voltage reference and an analog comparator to configure an interrupt generator useful in microprocessor applications. with the popularity of fast 486 and pentium laptop computers, the need to indicate a microprocessor overtemperature condition has grown tremendously. the circuit illustrated in figure 7 demonstrates one way to generate an interrupt using a tmp35, a cmp402 analog comparator, and a ref191, a 2 v precision voltage reference. the circuit has been designed to produce a logic high interrupt signal if the microprocessor temperature exceeds 80 c. this 80 c trip point was arbitrarily chosen (final value set by the microprocessor thermal reference design) and is set using an r3?4 voltage divider of the ref191? output voltage. since the output of the tmp35 is scaled by 10 mv/ c, the voltage at the cmp402? inverting terminal is set to 0.8 v. since temperature is a slowly moving quantity, the possibility for comparator chatter exists. to avoid this condition, hysteresis is used around the comparator. in this application, a hysteresis of 5 c about the trip point was arbitrarily chosen; the ultimate value for hysteresis should be determined by the end application. the output logic voltage swing of the comparator with r1 and r2 determine the amount of comparator hysteresis. u sing a 3.3 v supply, the output logic voltage swing of the cmp402 is 2.6 v; thus, for a hysteresis of 5 c (50 mv @ 10 mv/ c ), r1 is set to 20 k ? and r2 is set to 1 m ? . an expression for this circuit? hysteresis is given by: v hys = r 1 r 2 ? ? ? ? ? ? v logic swing , cmp 402 () because of the likelihood that this circuit would be used in close proximity to high speed digital circuits, r1 is split into equal values and a 1000 pf is used to form a low-pass filter on the output of the tmp35. furthermore, to prevent high frequency no ise from contaminating the comparato r trip point, a 0.1 f capacitor is used across r4. thermocouple signal conditioning with cold-junction compensation the circuit in figure 8 conditions the output of a type k thermocouple, while providing cold-junction compensation for temperatures between 0 c and 250 c. the circuit operates from single 3.3 v to 5.5 v supplies and has been designed to produce an output voltage transfer characteristic of 10 mv/ c. a type k thermocouple exhibits a seebeck coefficient of approximately 41 v/ c; therefore, at the cold junction, the tmp35, with a temperature coefficient of 10 mv/ c, is used with r1 and r2 to introduce an opposing cold-junction temperature coefficient of ?1 v/ c. this prevents the isothermal, cold-junction connection between the circuit? pcb tracks and the thermocouple? wires from introducing an error in the measured temperature. this compensation works extremely well for circuit ambient temperatures in the range of 20 c to 50 c. over a 250 c measurement temperature range, the thermocouple produces an output voltage change of 10.151 mv. since the required circuit? output full-scale voltage is 2.5 v, the gain of the circuit is set to 246.3. choosing r4 equal to 4.99 k ? sets r5 equal to 1.22 m ? . since the closest 1% value for r5 is 1.21 m ? , a 50 k ? potentiometer is used with r5 for fine trim of the full-scale output voltage. although the op193 is a superior single-supply, micropower operational amplifier, its output stage is not rail-to-rail; as such, the 0 c output voltage level is 0.1 v. if this circuit were to be digitized by a single-supply adc, the adc? common should be adjusted to 0.1 v accordingly. using tmp3x sensors in remote locations in many industrial environments, sensors are required to oper- ate in the presence of high ambient noise. these noise sources take on many forms; for example, scr transients, relays, radio transmitters, arc welders, ac motors, and so on. they may also be used at considerable distances from the signal conditioning circuitry. t hese high noise environments are very typically in the form of electric fields, so the voltage output of the tempera- ture sensor can be susceptible to contamination from these noise sources. r2 1m 3 4 v out v s tmp35 0.1 f gnd 0.1 f c1 interrupt <80 c >80 c ref191 r1a 10k r1b 10k 3.3v 2 6 c l 1000pf r3 16k 1 f r4 10k v ref 0.1 f 0.1 f c1 = cmp402 4 1 2 4 3 14 13 5 6 r5 100k figure 7. pentium overtemperature interrupt generator pentium is a registered trademark of intel corporation.
rev. c tmp35/tmp36/tmp37 ?1 a temperature to 4?0 ma loop transmitter in many process control applications, 2-wire transmitters are used to convey analog signals through noisy ambient environ- ments. these current transmitters use a ?ero-scale?signal current of 4 ma that can be used to power the transmitter? signal conditioning circuitry. the ?ull-scale?output signal in these transmitters is 20 ma. a circuit that transmits temperature information in this fashion is illustrated in figure 10. using a tmp3x as the temperature sensor, the output current is linearly proportional to the tem- perature of the medium. the entire circuit operates from the 3 v output of the ref193. the ref193 requires no external trimming for two reasons: (1) the ref193? tight initial output voltage tolerance and (2) the low supply current of tmp3x, the op193 and the ref193. the entire circuit consumes less than 3 ma from a total budget of 4 ma. the op193 regulates the output current to satisfy the current summation at the noninverting node of the op193. a generalized expression for the kcl equation at the op193? pin 3 is given by: i out = 1 r 7 ? ? ? ? ? ? tmp 3 x r 3 r 1 + v ref r 3 r 2 ? ? ? ? ? ? for each of the three temperature sensors, the table below illus- tr ates the values for each of the components, p1, p2, and r1?4: table ii. circuit element values for loop transmitter sensor r1( ) p1( )r2( ) p2( )r3( )r4( ) tmp35 97.6 k 5 k 1.58 m 100 k 140 k 56.2 k tmp36 97.6 k 5 k 931 k 50 k 97.6 k 47 k tmp37 97.6 k 5 k 10.5 k 500 84.5 k 8.45 k illustrated in figure 9 is a way to convert the output voltage of a tmp3x sensor into a current to be transmitted down a long twisted-pair shielded cable to a ground referenced receiver. the temperature sensors do not possess the capability of high output current operation; thus, a garden variety pnp transistor is used to boost the output current drive of the circuit. as shown in the table, the values of r2 and r3 were chosen to produce an arbi- trary full-scale output current of 2 ma. lower values for the full-scale current are not recommended. the minimum-scale output current produced by the circuit could be contaminated by nearby ambient magnetic fields operating in the vicinity of the circuit/cable pair. because of the use of an external transis- tor, the minimum recommended operating voltage for this circuit is 5 v. note, to minimize the effects of emi (or rfi), both the circuit? and the temperature sensor? supply pins are bypassed with good quality, ceramic capacitors. twisted pair belden type 9502 or equivalent tmp3x r2 r1 4.7k v out 0.1 f 2n2907 0.01 f gnd v s 5v r3 v out sensor r2 r3 tmp35 634 634 tmp36 887 887 tmp37 1k 1k figure 9. a remote, 2-wire boosted output current tem- perature sensor v out v s tmp35 0.1 f gnd op193 0.1 f r1 * 24.9k r4 4.99k r5 * 1.21m type k thermo- couple cu cu r2 * 102 v out 0v ?2.5v r6 100k 5% r3 10m 5% 3.3v < v s < 5.5v cold junction chromel alumel isothermal block note: all resistors 1% unless otherwise noted 0 c t 250 c 7 6 4 3 2 p1 50k figure 8. a single-supply, type k thermocouple signal conditioning circuit with cold-junction compensation
rev. c tmp35/tmp36/tmp37 ?2 the 4 ma offset trim is provided by p2, and p1 provides the circuit? full-scale gain trim at 20 ma. these two trims do not interact because the noninverting input of the op193 is held at a virtual ground. the zero-scale and full-scale output currents of the circuit are adjusted according to the operating temperature range of each temperature sensor. the schottky diode, d1, is required in this circuit to prevent loop supply power-on tran- sients from pulling the noninverting input of the op193 more than 300 mv below its inverting input. without this diode, such transients could cause phase reversal of the operational amplifier and possible latchup of the transmitter. the loop supply voltage compliance of the circuit is limited by the maximum applied input voltage to the ref193 and is from 9 v to 18 v. a temperature to frequency converter another common method of transmitting analog information from a remote location is to convert a voltage to an equivalent in the frequency domain. this is readily done with any of the low cost, monolithic voltage-to-frequency converters (vfcs) available. these vfcs feature a robust, open-collector output transistor for easy interfacing to digital circuitry. the digital signal produced by the vfc is less susceptible to contamination from external noise sources and line voltage drops because the only important information is the frequency of the digital signal. as long as the conversions between temperature and frequency are done accurately, the temperature data from the sensors can be reliably transmitted. the circuit in figure 11 illustrates a method by which the outputs of these temperature sensors can be converted to a frequency using the ad654. the output signal of the ad654 is a square wave that is proportional to the dc input voltage across pins 4 and 3. the transfer equation of the circuit is given by: f out = v tmp ? v offset 10 r t c t () ? ? ? ? ? ? ? ? tmp3x v s gnd 6 4 2 3 7 8 5 1 ad654 v out 10 f/0.1 f 5v p2 100k r off1 470 f out offset r off2 10 r1 p1 r t * 0.1 f c t * 5v r pu 5k f out nb: att a (min), f out = 0hz * r t and c t ?see table sensor r t (r1 + p1) c t tmp35 tmp36 tmp37 11.8k + 500 16.2k + 500 18.2k + 1k 1.7nf 1.8nf 2.1nf figure 11. a temperature-to-frequency converter an offset trim network (f out offset ) is included with this circuit to set f out at 0 hz when the temperature sensor? mini- mum output voltage is reached. potentiometer p1 is required to calibrate the absolute accuracy of the ad654. the table in figure 11 illustrates the circuit element values for each of the three sensors. the nominal offset voltage required for 0 hz output from the tmp35 is 50 mv; for the tmp36 and tmp37, the offset voltage required is 100 mv. in all cases for the circuit val ues shown, the output frequency transfer characteristic of the circuit was set at 50 hz/ c. at the receiving end, a frequency- to-voltage converter (fvc) can be used to convert the frequency back to a dc voltage for further process - ing. one such fvc is the ad650. for complete information on the ad650 and ad654, please consult the individual data sheets for those devices. v out 4 7 1 f r5 100k v out r l 250 v loop 9v to 18v 2 3 d1: hp5082?810 ref193 tmp3x r7 100 a1: op193 * see text for values r3 * r1 * v s r2 * p2 * 4ma adjust d1 r4 * r6 100k p1 * 20ma adjust gnd q1 2n1711 0.1 f 2 4 6 3v i l figure 10. a temperature to 4-to-20 ma loop transmitter
rev. c tmp35/tmp36/tmp37 ?3 driving long cables or heavy capacitive loads although the tmp3x family of temperature sensors is capable of driving capacitive loads up to 10,000 pf without oscillation, output voltage transient response times can be improved with the use of a small resistor in series with the output of the temperature sensor, as shown in figure 12. as an added benefit, this resistor forms a low-pass filter with the cable? capacitance, which helps to reduce bandwidth noise. since the temperature sensor is likely to be used in environments where the ambient noise level can be very high, this resistor helps to prevent rectification by the devices of the high frequency noise. the combination of this resistor and the supply bypass capacitor offers the best protection. tmp3x 0.1 f gnd +v s 750 long cable or heavy capacitive loads v out figure 12. driving long cables or heavy capacitive loads commentary on long-term stability the concept of long-term stability has been used for many years to describe by what amount an ic? parameter would shift dur- ing its lifetime. this is a concept that has been typically applied to both voltage references and monolithic temperature sensors. unfortunately, integrated circuits cannot be evaluated at room temperature (25 c) for 10 years or so to determine this shift. as a result, manufacturers very typically perform accelerated life- time testing of integrated circuits by operating ics at elevated temperatures (between 125 c and 150 c) over a shorter period of time (typically, between 500 and 1000 hours). as a result of this operation, the lifetime of an integrated circuit is significantly accelerated due to the increase in rates of reac- tion within the semiconductor material.
rev. c tmp35/tmp36/tmp37 ?4 3-pin plastic header-style package [to-92] (to-92) dimensions shown in inches and (millimeters) 0.115 (2.92) 0.080 (2.03) 0.115 (2.92) 0.080 (2.03) 0.165 (4.19) 0.125 (3.18) sq 0.019 (0.482) 0.016 (0.407) 0.105 (2.66) 0.095 (2.42) 0.055 (1.40) 0.045 (1.15) seating plane 0.500 (12.70) min 0.205 (5.21) 0.175 (4.45) 0.210 (5.33) 0.170 (4.32) 123 bottom view 0.135 (3.43) min 0.050 (1.27) max controlling dimensions are in inches; millimeters dimensions (in parentheses) are rounded-off equivalents for reference only and are not appropriate for use in design compliant to jedec standards to-226aa 8-lead standard small outline package [soic] narrow body (rn-8) dimensions shown in millimeters and (inches) 0.25 (0.0098) 0.19 (0.0075) 1.27 (0.0500) 0.41 (0.0160) 0.50 (0.0196) 0.25 (0.0099) 45 8 0 1.75 (0.0688) 1.35 (0.0532) seating plane 0.25 (0.0098) 0.10 (0.0040) 85 4 1 5.00 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2440) 5.80 (0.2284) 0.51 (0.0201) 0.33 (0.0130) coplanarity 0.10 controlling dimensions are in millimeters; inch dimensions (in parentheses) are rounded-off millimeter equivalents for reference only and are not appropriate for use in design compliant to jedec standards ms-012aa 5-lead plastic surface-mount package [sot-23] (rt-5) dimensions shown in millimeters pin 1 1.60 bsc 2.80 bsc 1.90 bsc 0.95 bsc 1 3 4 5 2 0.22 0.08 0.60 0.45 0.30 10 0 0.50 0.30 0.15 max seating plane 1.45 max 1.30 1.15 0.90 compliant to jedec standards mo-178aa 2.90 bsc outline dimensions revision history location page 10/02?ata sheet changed from rev. b to rev. c. deleted text from commentary on long-term stability section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 update outline dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
?5
?6 c00337??0/02(c) printed in u.s.a.

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