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1 astec semiconductor AS273 over-temperature detector features programmable to three different over-temperature thresholds 2.5 v temperature compensated bandgap reference trimmed to 1% open collector output goes low on over-temp condition 3?c temperature accuracy reference shunt current serves to program over-temp threshold available with 5?c or 10?c of temperature hysteresis available in a wide range of over- temp thresholds to fit most temperature monitoring applications now available in the sot-223 for improved substrate temperature sensing description the AS273 is a series of programmable over-temperature detectors. each is internally composed of a precision 2.5 v shunt reference, a proportional-to-absolute temperature thermal sensor, a comparator with controlled hysteresis, and an open collector output that indicates an over-temp condi- tion. the threshold for the over-temp signal can be set to any of three values on a given part by controlling the magnitude of the reference shunt current. the AS273 has an excellent absolute temperature accuracy of 3?c for each of the three over-temp thresholds. the low power dissipation minimizes any temperature sensing errors due to self-heating. there is either 5?c or 10?c of tempera- ture hysteresis to prevent bouncing when an over-temp con- dition is removed. the packaging options available with the AS273 make it appealing to a wide variety of temperature-sensing applica- tions. the to-92 package can be mechanically clamped to a heat sink to monitor the temperature of power devices. the 8l-soic and sot-223 surface mount packages allow for temperature sensing in high component density applications. semiconductor pin configuration ? top view out to-92 (lp) sot-223 (g) ground v ref out ground v ref soic (d) vref do not use do not use ground out n/c n/c n/c 1 2 3 4 8 7 6 5
2 astec semiconductor AS273 over -t emperature detector ordering information functional block diagram pin function description pin number function description 1 v ref 2.5 v shunt reference; current into v ref pin also programs over-temperature trip point to one of three t ot values 2 gnd circuit ground and silicon substrate 3 out open collector output. output low when die temperature exceeds programmed trip point cir cuit t ype: over -t emperature detector t emperature option: (refer to t able a) packaging option: a b t 13 package style: d g lp hysteresis option: 1 5 = ammo pack = bulk = t ube = t ape and reel (13" reel dia) = soic = sot -223 = to-92 = 10 c = 5 c AS273 d 1 d a e + current programming 1 3 2 v ref 2.5 v + e gnd out 4 mv/k t able a ?t emperatur e options code t ot1 t ot2 t ot3 d 40 45 50 f 75 80 85 g 90 95 100 h 105 110 115
3 astec semiconductor AS273 over -t emperature detector absolute maximum ratings parameter symbol rating unit reference current v ref 10 ma output current i out 10 ma output v oltage v out 18 v continuous power dissipation at 25 ? c t o-92 p d 775 mw 8-soic p d 750 mw sot -223 p d 1000 mw junction t emperature t j 150 ? c storage t emperature t stg e65 to 150 ? c lead t emp, soldering 10 seconds t l 300 ? c stresses greater than those listed under absolute maximum ra tings may cause permanent damage to the device. this is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operati onal sec - tions of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may af fect reliability . t ypical thermal resistances package q ja q jc t ypical derating sot -223 1 15 ? c/w 8 ? c/w 8.7 mw/ ? c t o-92 160 ? c/w 80 ? c/w 6.3 mw/ ? c 8l soic 175 ? c/w 45 ? c/w 5.7 mw/ ? c
4 astec semiconductor AS273 over -t emperature detector electrical characteristics electrical characteristics are guaranteed over the full junction temperature range (0 to 125 ? c). ambient temperature must be derated based upon power dissipation and package thermal characteristics. parameter symbol t est condition min. t yp. max. unit reference reference v oltage v ref i ref = 2 ma, t j = 25 ? c 2.500 2.525 2.550 v load regulation v id 0.65 ma i ref 5.5 ma 5 10 mv a verage t emperature coef ficient d v reg / d t 0.65 ma i ref 5.5 ma 75 ppm/ ? c output saturation v oltage v ol i out = 4 ma; t j > t ot 200 400 mv breakdown v oltage bv i out = 100 m a; t j < t ot 18 30 v leakage current i oh v out = 18 v ; t j < t ot 1 1000 na over-t emp sensing t emperature accuracy t ot(1) 0.7 ma i ref 1.3 ma e3 +3 ? c t ot(2) 1.55 ma i ref 2.6 ma e3 +3 ? c t ot(3) 3.0 ma i ref 5.0 ma e3 +3 ? c hysteresis h ot percentage error in nominal hysteresis e30 +30 % +5v i ref out v ref gnd AS273 r load 2 k w t est circuit figure 1. t est circuit for output hysteresis curve
5 astec semiconductor AS273 over -t emperature detector t ypical performance curves figure 2 figure 4 figure 3 figure 5 0 25 50 75 100 125 150 300 275 250 225 200 175 150 125 100 minimum reference current for regulation junction t emperature, t j ( c) t urn-on current, i ref ( m a) 0 200 400 600 800 1000 3 2 1 0 t urn-on characteristic of reference reference current, i ref ( m a) reference v oltage, v ref (v) 0 25 50 75 junction t emperature, t j ( c) 100 125 150 2.55 2.54 2.53 2.52 2.51 2.50 t emperature regulation of reference reference v oltage, v ref (v) 0 25 50 75 junction t emperature, t j ( c) 100 125 150 10 9 8 7 6 5 4 3 2 1 0 load regulation of reference over -temperature load regulation (mv)
6 astec semiconductor AS273 over -t emperature detector t ypical performance curves figure 6 figure 8 figure 7 0.001 0.01 0.1 1 10 900 800 700 600 500 400 300 200 100 output saturation characteristic output v oltage, v out (mv) 125 c 100 c 75 c 50 c 25 c 0 c saturation current, i out (ma) 88 90 92 94 over -temperature threshold ( c) 96 98 100 102 0 10 20 30 40 50 i ref = 1 ma i ref = 2 ma i ref = 4 ma t ypical over -temperature threshold distribution ?option g distribution of population (%) 0 2 4 6 8 10 12 120 100 80 60 40 20 0 8l soic to-92 sot -223 t ime (s) per cent of thermal equilibrium (%) thermal response by package in a stirred oil bath
7 astec semiconductor theory of operation the AS273 is an over-temperature detector that gives an over-temp signal when the device junction temperature exceeds a programmed over-temp threshold. over-temp threshold pro - gramming is accomplished by controlling the magnitude of the reference shunt current. over-temperature condition internal to the AS273 is a temperature sensor which creates a voltage proportional to the absolute temperature (pt a t) of the die. this pt a t voltage is compared with a fraction of the reference voltage corresponding to the over- temperature threshold. when the pt a t voltage exceeds the reference voltage, the comparator is tripped and an over-temp signal is given to the output. the output consists of an open collector transistor that pulls low on an over-temp condi - tion. built into the comparator is temperature hys - teresis, which keeps the over-temp signal until the junction temperature has fallen 5 ? c (or 10 ? c) below the over-temp threshold. figure 9 shows the output of the AS273 (with 10 ? c of hysteresis) over a range of junction temperature. AS273 over -t emperature detector figure 9. t emperature characteristic of output with 10 ? c of hysteresis 5 0 i ref = 4 ma 5 0 i ref = 2 ma 5 0 i ref = 1 ma ot1 ot2 ot3 ot1-5 ot1-10 output voltage, v junction temperature, t j ( c)
8 astec semiconductor current programming there are three dif ferent over-temp thresholds for each AS273. the detector senses the amount of current being shunted through the 2.5 v refer - ence of pin 1 and programs an over-temp thresh - old based on the magnitude of that current. fig - ure 10 illustrates the ranges of reference shunt current, i ref , associated with each of the three over-temp thresholds, ot1, ot2 and ot3. AS273 over -t emperature detector figure 10. reference shunt current programming ranges of over-temperature thresholds ot3 ot2 ot1 0 1 2 3 4 5 over-temperature thresholds ( c) reference shunt current, i ref (ma) output disabled transition regions
9 astec semiconductor t ypical detector applications over-t emperature detector the AS273 senses the ambient temperature and turns on its open collector output to indicate an over-temp condition. each AS273 can be pro - grammed to any one of its three over-temp thresholds by forcing a dif ferent range of current into the reference pin. dual speed fan control the diagram of figure 12 shows an easy way to implement smart fan control. when the tempera - ture is below the over-temp trip point set by r1, the detector ? s open collector output is of f. there - fore, the fan speed is controlled by the ratio between r2 and r3. when the temperature exceeds the over-temp set point, the open col - lector is turned on, and fan motor runs at its full speed. AS273 over -t emperature detector figure 1 1. figure 12. v cc r2 r1 v out ref out gnd AS273 +12 v r1 9.1 k w ref out gnd AS273 r2 10 k w r3 10 k w q1 m
10 astec semiconductor AS273 over -t emperature detector over-t emperature protection with latch (low current) the diagram of figure 13 illustrates how a power supply can be shut down with a simple two- transistor latch. when the programmed over- temp is reached, the open collector output of the AS273 enables the latch and pulls v cc below the under-voltage threshold of the as3842, shutting of f the as3842. the latch can be disabled only with a power reset. over-t emperature protection with hysteresis in this over-temperature circuit, the hysteresis of the AS273 is used to automatically restart the power supply after the temperature drops below the hysteresis temperature window . r1 supplies the current to power the AS273 after the as3842 and the power supply are shut down. r2 and the external zener set the over-temperature trip point. figure 13. figure 14. v cc i cc = 400 ma max. ref out gnd AS273 comp v reg v fb v cc sense out rt/ct gnd as3842 r1 1 k r3 350 w + r2 350 w v bulk r1 ref out gnd AS273 r2 comp v reg v fb v cc sense out rt/ct gnd as3842
11 astec semiconductor AS273 over -t emperature detector adjustable hysteresis t emperature detector the hysteresis of the AS273 can be increased by reprogramming the device to a lower tempera - ture set point upon over-temp. a higher tempera - ture is set by r1. when the temperature exceeds the high-temp set point, the open collector output is turned on and allows r2 to rob current from the reference pin and resets the AS273 to the low- temp set point. as a result, the hysteresis esca - lates by the dif ference between the high-temp and the low-temp set points. three-state t emperature sensor in the three-state t emperature sensor shown in figure 16, a low-temp trip point is selected by r1 and a high-temp trip point is selected by the two- transistor latch. when the temperature is below the low-temp set point, v out is in the high state (v out = 5.0 v). when the temperature exceeds the low-temp set point, the two-transistor latch is set and v out is pulled low (v out = 2.5 v). the latch also supplies extra current to the reference pin to reset the ic to sense a higher temperature. once the high-temp is reached, the output will turn on (v out = 0.2 v). this circuit is highly use - ful in applications where a stand-by , a warning and a shut-down state are required. figure 15. figure 16. v cc r2 r1 v out ref out gnd AS273 v cc +5 v r1 2.4 k w ref out gnd AS273 r2 1 k w r3 1.5 k w r5 2 k w r4 470 w r6 500 w + v o c1 1 m f stand-by state: warning state: shut-down state: t < t1, t2 t1 < t < t2 t1, t2 < t v o = 5.0 v v o = 2.5 v v o = 0.2 v
12 astec semiconductor AS273 over -t emperature detector notes

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