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_______________general description the icl7665 warns microprocessors ( ps) of overvolt- age and undervoltage conditions. it draws a typical operating current of only 3a. the trip points and hys- teresis of the two voltage detectors are individually pro- grammed via external resistors to any voltage great er than 1.3v. the icl7665 wil l operate fr om any supply voltage in the 1.6v to 16v range, while monitoring volt- ages fr om 1.3v to several hundred vol ts . the maxim icl7665a is an improved version wi th a 2%-accurate v set 1 th reshold and guaranteed performance over temperature. the 3a quiescent cu rrent of th e icl7665 makes it ideal for voltage monito ri ng in battery-powered sys- tems. in both battery- and line -p ow er ed systems, the unique combination of a reference, two comparators, and hyste re sis ou tp uts reduces the si ze and compo- nent count of many circuits. ________________________applications p voltage monitoringlow-battery detection power-fail and brownout detection battery backup switching power-supply fault monitoring over/undervoltage protection high/low temperature, pressure, voltage alarms ____________________________features p over/undervoltage warningimproved second source dual comparator with precision internal r ef erence 3a operating current2% threshold accuracy (icl7665a) 1.6v to 16v supply voltage range on-board hysteresis outputs externally programmable trip points monolithic, low-power cmos design ______________ordering information ordering information continued on last page. icl7665 microprocessor voltage monitor with dual over/undervoltage detection ________________________________________________________________ maxim integrated products 1 1 + 23 4 87 6 5 out2set2 hyst2 gnd set1 hyst1 out1 icl7665 dip/so top view v+ _________________pin configurations icl7665 out1 out2 set2 set1 v+ v in2 v in1 v+ 84 1 7 6 3 gnd overvoltage detection undervoltage detection simple threshold detector nmi __________typical operating circuit 19-0001; rev 3; 11/15 part temp. range pin-package icl7665cpa 0c to +70c 8 plastic dip icl7665acpa 0c to +70c 8 plastic dip icl7665bcpa 0c to +70c 8 plastic dip icl7665csa 0c to +70c 8 so icl7665acsa 0c to +70c 8 so icl7665bcsa 0c to +70c 8 so icl7665cja 0c to +70c 8 cerdip icl7665acja 0c to +70c 8 cerdip icl7665bcja 0c to +70c 8 cerdip + + + + ++ + ++ +denotes a lead(pb)-free/rohs-compliant package. downloaded from: http:///
i cl7 6 6 5 m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v+ = 5v, t a = +25c, unless otherwise noted.) stresses beyond those listed under absolute maximu m ratings may cause permanent damage to the device . these are stress ratings only, and functional operation of the device at these or any other condi tions beyond those indicated in the operational sec tions of the specifications is not implied. exposur e to absolute maximum rating conditions for extended per iods may affect device reliability. note 1: due to the scr structure inherent in the cmos proce ss used to fabricate these devices, connecting any terminal to volt- ages greater than (v+ + 0.3v) or less than (gnd - 0 .3v) may cause destructive latchup. for this reason , we recommend that inputs from external sources that are not oper ating from the same power supply not be applied to the device before its supply is established, and that in multiple supply systems, the supply to the icl7665 be turned on fir st. if this is not possi- ble, currents into inputs and/or outputs must be li mited to 0.5ma and voltages must not exceed those defined above. supply voltage (note 1) ............................ .............-0.3v to +18v output voltages out1 and out2 (with respect to gnd) (note 1) ..................... .....-0.3v to +18v output voltages hyst1 and hyst2 (with respect to v+) (note 1) ...................... .......+0.3v to -18v input voltages set1 and set2 (note 1)........................................(gn d - 0.3v) to (v+ + 0.3v) maximum sink output current out1 and out2...................................... .......................25ma maximum source output current hyst1 and hyst2 .................................... ....................-25ma continuous power dissipation (t a = +70 c) plastic dip (derate 9.09mw/c above +70 c) ............727mw so (derate 5.88mw/c above +70 c) ........................471mw cerdip (derate 8.00mw/c above +70 c) ................640mw to-99 (derate 6.67mw/c above +70 c) ...................533mw operating temperature ranges icl7665c_ _........................................ ...............0c to +70c icl7665i_ _ ........................................ .............-20c to +85c icl7665e_ _........................................ ............-40c to +85c storage temperature range .......................... ...-65c to +160c lead temperature (soldering, 10sec) ................ .............+300c parameter symbol conditions min typ max units operating supply voltage v+ icl7665 t a = +25c 1.6 16 v t a = t min to t min 1.8 16 icl7665a t a = t min to t min 2.0 16 icl7665b t a = +25c 1.6 10 input trip voltage v set icl7665, icl7665b, t a = +25c v set1 1.150 1.300 1.450 v v set2 1.200 1.300 1.400 icl7665a, t a = +25c v set1 1.275 1.300 1.325 v set2 1.225 1.300 1.375 icl7665a, t a = t min to t max v set1 1.250 1.300 1.350 v set2 1.215 1.300 1.385 v set tempco 100 ppm/c r out1 , r out2 , r hyst1 , r hyst2 = 1m 0.004 %/v supply current i+ gnd v set1, v set2 v+, all outputs open circuit v+ = 2v 2.5 10 m a v+ = 9v 2.6 10 v+ = 15v 2.9 15 icl7665b, t a = +25c v+ = 2v 2.5 10 v+ = 9v 2.6 10 t a = t min to t min 1.8 10 icl7665, t a = +25c; icl7665a, t a = t min to t max supply voltage sensitivity of v set1 , v set2 downloaded from: http:///
i cl7 6 6 5 m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion _______________________________________________________________________________________ 3 electrical characteristics (continued) (v+ = 5v, t a = +25c, unless otherwise noted.) parameter conditions min typ max units output leakage current i olk , i hlk all grades, v set = 0v or v set 3 2v, t a = +25c out1, out2 10 200 na hyst1, hsyt2 -10 -100 out1, out2 2000 hyst1, hsyt2 -500 icl7665b, v+ = 9v, t a = t min to t max out1, out2 2000 hyst1, hsyt2 -500 v out1 saturation voltage v set1 = 2v, i out1 = 2ma icl7665, icl7665b: v+ = 2v 0.20 0.50 icl7665a: v+ = 2v 0.20 all grades: v+ = 5v 0.10 0.30 icl7665, icl7665a: v+ = 15v 0.06 0.20 icl7665b: v+ = 9v 0.06 0.25 all grades: v+ = 2v -0.15 -0.30 all grades: v+ = 5v -0.05 -0.15 icl7665, icl665a: v+ = 15v -0.02 -0.10 icl7665b: v+ = 9v -0.02 -0.15 v out2 saturation voltage v set2 = 0v, i out2 = 2ma all grades: v+ = 2v 0.20 0.50 v all grades: v+ = 5v 0.15 0.30 icl7665, icl665a: v+ = 15v 0.11 0.25 icl7665b: v+ = 9v 0.11 0.30 v hyst2 saturation voltage all grades: v+ = 2v -0.25 -0.80 v all grades: v+ = 5v -0.43 -1.00 icl7665: v+ = 15v -0.35 -0.80 icl7665a: v+ = 15v -0.35 -1.00 icl7665b: v+ = 9v -0.35 -1.00 i set gnd v set v+ 0.01 10 na d v set 0.1 mv v set1 C v set2 5 50 mv 0.1 mv symbol v v hyst1 saturation voltage v v set1 = 2v, i hyst1 = -0.5ma icl7665, icl7665a, v+ = 15v, t a = t min to t max v set2 = 2v, i hyst2 = - 0.2ma v set2 = 2v, i hyst2 = - 0.5ma v set input leakage current r out , r hyst = 1m w r out , r hyst = 1m w r out = 4.7k w , r hyst = 20k w , v out lo = 1% v+, v out hi = 99% v+ v set input change for complete output change difference in trip voltage output/hysteresis difference downloaded from: http:///
i cl7 6 6 5 m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion 4 _______________________________________________________________________________________ ac operating characteristics (v+ = 5v, t a = +25c, unless otherwise noted.) v set switched between 1.0v and 1.6v, r out = 4.7k , c l = 12pf, r hyst = 20k s 1.8 t h2f output fall times 4.0 t h1f 0.7 t o2f 0.6 t o1f v set switched between 1.0v and 1.6v, r out = 4.7k , c l = 12pf, r hyst = 20k s 0.7 t h2r output rise times 7.5 t h1r 0.8 t o2r 0.6 t o1r v set switched from 1.6v to 1.0v, r out = 4.7k , c l = 12pf, r hyst = 20k s 60 t s h2d output delay time, input going low 60 t s o2d 80 t s h1d 75 t s o1d v set switched from 1.0v to 1.6v, r out = 4.7k , c l = 12pf, r hyst = 20k conditions s 55 t sh2d output delay time, input going high 55 t so2d 90 t sh1d 85 t so1d units min typ max symbol parameter input out1 hyst1 out2 hyst2 t o1f t so 1d t h1r t so2d t sh2d t o2r t o2f t sh2d t o1r 1.6v 1.0v v+ (5v) gnd v+ (5v) gnd v+ (5v) gnd v+ (5v) gnd v set1, v set2 t sh1d t h2r t h2f t so2d t sh1d t h1f t so1d ___________________________________________________ ____sw it c hing wa ve for m s downloaded from: http:///
i cl7 6 6 5 m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion _______________________________________________________________________________________ 5 2.0 0 0 15 out1 saturation voltage as a function of output current 0.5 1.5 icl7665-01 i out out1 (ma) voltage saturation (v) 1.0 10 5 20 v+ = 2v v+ = 9v v+ = 15v v+ = 5v supply current as a function of supply voltage supply current ( m a) 0 0 supply voltage (v) icl7665-02 2 4 6 8 10 12 14 16 0.5 1.0 t a = +25c t a = +70c 0v v set1 , v set2 v+ 1.5 2.0 2.5 3.0 3.5 5.0 4.5 4.0 t a = -20c supply current as a function of am bient tem perature -20 0 20 40 60 ambient temperature (c) icl7665-03 supply current ( m a) 0 0.5 1.5 2.0 2.5 3.0 3.5 4.0 5.0 1.0 4.5 v+ = 15v v+ = 9v v+ = 2v 0v v set1 , v set2 v+ -2.0 -1.6 -1.2 -0.8 -0.4 0 -20 -16 -12 -8 -4 0 hyst1 output saturation voltage vs. hyst1 output current hyst1 output saturation voltage (v) hyst1 output current (ma) icl7665-04 v+ = 2v v+ = 5v v+ = 9v v+ = 15v -5 -4 -3 -2 -1 0 -5 -4 -3 -2 -1 0 hyst2 output saturation voltage vs. hyst2 output current hyst2 output saturation voltage (v) hyst2 output current (ma) icl7665-05 v+ = 2v v+ = 15v v+ = 9v v+ = 5v 2.0 1.5 1.0 0.5 0 20 15 10 5 0 out2 saturation voltage as a function of output current voltage saturation (v) i out out2 (ma) icl7665-06 v+ = 2v v+ = 5v v+ = 9v v+ = 15v __________________________________________typic a l o pe ra t ing cha ra c t e rist ic s (t a = +25c, unless otherwise noted.) downloaded from: http:///
i cl7 6 6 5 _______________de t a ile d de sc ript ion as shown in the block diagram of figure 2, the maxi m icl7665 combines a 1.3v reference with two com- parators, two open-drain n-channel outputs, and two open-drain p-channel hysteresis outputs. the refer- ence and comparator are very low-power linear cmos circuits, with a total operating current of 10 m a maxi- mum, 3 m a typical. the n-channel outputs can sink greater than 10ma, but are unable to source any cur - rent. these outputs are suitable for wire-or connec tions and are capable of driving ttl inputs when an exter nal pull-up resistor is added. the icl7665 truth table is shown in table 1. out1 i s an inverting output; all other outputs are noninver ting. hyst1 and hyst2 are p-channel current sources whose sources are connected to v+. out1 and out2 are n-channel current sinks with their sources conn ect- ed to ground. both out1 and out2 can drive at least one ttl load with a v ol of 0.4v. in spite of the very low operating current, the icl 7665 has a typical propagation delay of only 75 m s. since the comparator input bias current and the output leakag es are very low, high-impedance external resistors can be used. this design feature minimizes both the total sup- ply current used and loading on the voltage source that is being monitored. m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion 6 _______________________________________________________________________________________ figure 1. test circuit hyst2 = off = low out2 = on = low v set2 < 1.3v hyst2 = on = hi out2 = off = hi v set2 > 1.3v hyst1 = off = low out1 = off = hi v set1 < 1.3v hyst1 = on = hi out1 = on = low v set1 > 1.3v hysteresis output input* table 1. icl7665 truth table v+ hyst1 hyst2 out1 out2 to v+ set2 set1 1.3v bandgap reference figure 2. block diagram 1 2 3 4 8 7 6 5 icl7665 out1 hyst1 set1 gnd v+ out2 set2 hsyt2 12pf 12pf 12pf 12pf out1 hyst1 out2 hsyt2 4.7k 4.7k v+ 1.6v 1.0v input 20k 20k * see electrical characteristics out1 is an inverting output; all others are noninve rting. out1 and out2 are open-drain, n-channel current sinks. h yst1 and hyst2 are open-drain, p-channel current sinks. downloaded from: http:///
ba sic ove r/u nde rvolt a ge de t e c t ion circ uit s figures 3, 4, and 5 show the three basic voltage de tec- tion circuits. the simplest circuit, depicted in figure 3, does no t have any hysteresis. the comparator trip-point form ulas can easily be derived by observing that the compara tor changes state when the v set input is 1.3v. the exter- nal resistors form a voltage divider that attenuate s the input signal. this ensures that the v set terminal is at 1.3v when the input voltage is at the desired compa ra- tor trip point. since the bias current of the compa rator is only a fraction of a nanoamp, the current in the volt- age divider can be less than one microamp without l os- ing accuracy due to bias currents. the icl7665a has a 2% threshold accuracy at +25c, and a typical tempe r- ature coefficient of 100ppm/c including comparator offset drift, eliminating the need for external pot en- tiometers in most applications. figure 4 adds another resistor to each voltage dete ctor. this third resistor supplies current from the hyst out- put whenever the v set input is above the 1.3v thresh- old. as the formulas show, this hysteresis resistor affects only the lower trip point. hysteresis (defi ned as the difference between the upper and lower trip poi nts) keeps noise or small variations in the input signal from repeatedly switching the output when the input sign al remains near the trip point for a long period of ti me. the third basic circuit, figure 5, is suitable only when the voltage to be detected is also the power-supply vol tage for the icl7665. this circuit has the advantage that al l of the current flowing through the input divider resistors flows through the hysteresis resistor. this allows the us e of higher-value resistors, without hysteresis output l eakage having an appreciable effect on the trip point. resistor-value calculations figure 3 1) choose a value for r11. this value determines the amount of current flowing though the input divider, equal to v set / r11. r11 can typically be in the range of 10k w to 10m w . 2) calculate r21 based on r11 and the desired trip point: v trip C v set v trip C 1.3v r21 = r11 ( ) = r11 ( ) v set 1.3v i cl7 6 6 5 m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion _______________________________________________________________________________________ 7 figure 3. simple threshold detector figure 4. thre shold detector with hysteresis icl7665 out1 out2 set2 set1 r21 r11 r22 r12 v in1 v+ v in2 out1 v in1 v trip1 v trip2 out2 v in2 icl7665 out1 out2 set2 set1 r21 r11 r22 r12 v in1 v+ v in2 hyst1 hyst2 r31 r32 v+ out1 v l1 v u1 0v v+ v u2 out2 v in1 0v v l2 v in2 downloaded from: http:///
i cl7 6 6 5 m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion 8 _______________________________________________________________________________________ figure 4 1) choose a resistor value for r11. typical values are in the 10k w to 10m w range. 2) calculate r21 for the desired upper trip point, v u, using the formula: v u - v set v u C 1.3v r21 = r11 ( ) = r11 ( ) v set 1.3v 3) calculate r31 for the desired amount of hysteresis: (r21) (v+ C v set ) (r21) (v+ C 1.3v) r31 = = v u C v l v u C v l or, if v+ = v in : (r21) (v l C v set ) (r21) (v l C 1.3v) r31 = = v u C v l v u C v l 4) the trip voltages are not affected by the absolute value of the resistors, as long as the impedances are high enough that the resistance of r31 is much greater than the hyst outputs resistance, and the current through r31 is much higher than the hyst outputs leakage current. normally, r31 will be in the 100k w to 22m w range. multiplying or dividing all three resistors by the same factor wil l not affect the trip voltages. figure 5 1) select a value for r11, usually between 10k w and 10m w . 2) calculate r21: v l C v set v l C 1.3v r21 = r11 ( ) = r11 ( ) v set 1.3 3) calculate r31: v u C v l r31 = r11 ( ) v set 4) as in the other circuits, all three resistor values may be scaled up or down in value without changing v u and v l . v u and v l depend only on the ratio of the three resistors, if the absolute values are such th at the hysteresis output resistance and the leakage currents of the v set input and hysteresis output can be ignored. __________applic a t ions i nform a t ion fa ult m onit or for a single supply figure 6 shows a typical over/undervoltage fault mo nitor for a single supply. in this case, the upper trip p oints (con- trolling out1) are centered on 5.5v, with 100mv of hys- teresis (v u = 5.55v, v l = 5.45v); and the lower trip points (controlling out2) are centered on 4.5v, also with 100mv of hysteresis. out1 and out2 are connected together in a wire-or configuration to generate a power-ok sign al. m ult iple -supply fa ult m onit or the icl7665 can simultaneously monitor several powe r supplies, as shown in figure 7. the easiest way to calculate the resistor values is to note that when the v set input is at the trip point (1.3v), the current through r11 is 1 .3v / r11. the sum of the currents through r21a, r21b and r31 must equal this current when the two input voltages are at the desired low-voltage detection point. ordinarily, r2 1a and r21b are chosen so that the current through the two resis- tors is equal. note that, since the voltage at the icl7665 v set input depends on the voltage of both supplies being monitored, there will be some interaction between t he low- voltage trip points for the two supplies. in this e xample, out1 will go low when either supply is 10% below no minal (assuming the other supply is at the nominal voltag e), or when both supplies are 5% or more below their nomin al voltage. r31 sets the hysteresis, in this case, to about 43mv at the 5v supply or 170mv at the 15v supply. the se cond section of icl7665 can be used to detect overvoltag e or, as shown in figure 7, can be used to detect the absenc e of negative supplies. note that the trip points for ou t2 depend on both the voltages of the negative power supplies and the actual voltage of the +5v supply. figure 5. threshold detector, v in = v+ v l2 v u2 icl7665 out1 out2 set2 set1 r21 r11 v in hyst1 hyst2 out1 out2 v in v+ gnd overvoltage undervoltage r31 r32 r22 r12 v l1 v u1 downloaded from: http:///
i cl7 6 6 5 m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion _______________________________________________________________________________________ 9 com bina t ion low -ba t t e ry wa rning a nd low -ba t t e ry disc onne c t nickel cadmium (nicd) batteries are excellent recha rge- able power sources for portable equipment, but care must be taken to ensure that nicd batteries are not damaged by overdischarge. specifically, a nicd batt ery should not be discharged to the point where the pol arity of the lowest-capacity cell is reversed, and that c ell is reverse charged by the higher-capacity cells. this reverse charging will dramatically reduce the life of a nic d battery. the figure 8 circuit both prevents reverse charging and gives a low-battery warning. a typical low-battery warning voltage is 1v per cell. since a nicd 9v battery i s ordi- narily made up of six cells with a nominal voltage of 7.2v, a low-battery warning of 6v is appropriate, with a small hysteresis of 100mv. to prevent overdischarge of a bat- tery, the load should be disconnected when the batt ery voltage is 1v x (n C 1), where n = number of cells. in this case, the low-battery load disconnect should occur at 5v. since the battery voltage will rise when the lo ad is disconnected, 800mv of hysteresis is used to preven t repeated on/off cycling. pow e r-fa il wa rning a nd pow e r-u p/pow e r-dow n re se t figure 9 illustrates a power-fail warning circuit t hat monitors raw dc input voltage to the 7805 three-ter mi- nal 5v regulator. the power-fail warning signal goe s high when the unregulated dc input falls below 8.0v . when the raw dc power source is disconnected or the ac power fails, the voltage on the input of the 780 5 decays at a rate of i out / c (in this case, 200mv/ms). since the 7805 will continue to provide a 5v output at 1a until v in is less than 7.3v, this circuit will give at least 3.5ms of warning before the 5v output begins to drop. if additional warning time is needed, either the trip voltage or filter capacitance should be increa sed, or the output current should be decreased. the icl7665 out2 is set to trip when the 5v output has decayed to 3.9v. this output can be used to prevent the microprocessor from writing spurious data to a cmos battery-backup memory, or can be used to acti- vate a battery-backup system. ac pow e r-fa il a nd brow nout de t e c t or by monitoring the secondary of the transformer, the cir- cuit in figure 10 performs the same power-failure w arn- ing function as figure 9. with a normal 110v ac inp ut to the transformer, out1 will discharge c1 every 16.7ms when the peak transformer secondary voltage exceeds 10.2v. when the 110v ac power-line voltage is either interrupted or reduced so that the peak v oltage is less than 10.2v, c1 will be charged through r1. out2, the power-fail warning output, goes high when the voltage on c1 reaches 1.3v. the time constant r 1 x c1 determines the delay time before the power-fail warning signal is activated, in this case 42ms or 2 1 M 2 line cycles. optional components r2, r3 and q1 add hysteresis by increasing the peak secondary voltage required to d is- charge c1 once the power-fail warning is active. ba t t e ry sw it c hove r circ uit the circuit in figure 11 performs two functions: sw itch- ing the power supply of a cmos memory to a backup battery when the line-powered supply is turned off, and lighting a low-battery-warning led when the backup battery is nearly discharged. the pnp transistor, q 1, connects the line-powered +5v to the cmos memory whenever the line-powered +5v supply voltage is greater than 3.5v. the voltage drop across q1 will only be a couple of hundred millivolts, since it will be satu- rated. whenever the input voltage falls below 3.5v, out1 goes high, turns off q1, and connects the 3v lithium cell to the cmos memory. the second voltage detector of the icl7665 monitors the voltage of the lithium cell. if the battery voltage falls below 2.6v, out2 goes low and the low-battery-warning led turns on (assuming that the +5v is present, of cour se). another possible use for the second section of the icl7665 is the detection of the input voltage falli ng below 4.5v. this signal could then be used to preve nt the microprocessor from writing spurious data to th e cmos memory while its power-supply voltage is out- side its guaranteed operating range. sim ple h igh/low t e m pe ra t ure ala rm the circuit in figure 12 is a simple high/low tempe ra- ture alarm, which uses a low-cost npn transistor as the sensor and an icl7665 as the high/low detector. the npn transistor and potentiometer r1 form a vbe mult i- plier whose output voltage is determined by the vbe of the transistor and the position of r1s wiper arm. the voltage at the top of r1 will have a temperature co effi- cient of approximately -5mv/c. r1 is set so that t he voltage at v set2 equals the v set2 trip voltage when the temperature of the npn transistor reaches the level selected for the high-temperature alarm. r2 can be adjusted so that the voltage at v set1 is 1.3v when the npn transistors temperature reaches the low-temper a- ture limit. downloaded from: http:///
i cl7 6 6 5 m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion icl7665 out2 out1 set1 set2 hyst2 hyst1 r31 22m 22m 100k power ok 301k r11 49.9k v+ +5v -5v -15v 787k +5v +15v r21a 274k r21b 1.02m +5v hyst1 set1 hyst2 set2 gnd out2 v+ v+ out1 out2 shdn sense icl7663 icl7665 gnd low-battery warning low-battery shutdown +5v, 1a output r31 out1 set r21 r11 r32 r22 r12 1m 100 w figure 8. low-battery warning and low-battery disc onnect figure 7. multiple-supply fault monitor hyst1 set1 hyst2 set2 icl7665 v+ unregulated dc input back-up battery reset or write enable power-fail warning 4700f 470f 2.2m 1m 5.6m 715k 130k 22m out2 out1 5v, 1a output 7805 5v regulator hyst1 set1 hyst2 set2 out1 out2 icl7665 v+ 7805 5v regulator 10vac 60hz 20v center tapped trans 4700 m f r2 1m 681k q1 r3 1m c1 r1 +5v power-fail warning 100k 5v, 1a figure 9. power-fail warning and power-up/power-do wn reset figure 10. ac power-fail and brownout detector icl7665 out1 out2 set2 set1 +5v supply hyst1 hyst2 v+ 13m 5% 7.5m 5% 249k 324k 100k 100k overvoltage detector v u ? 5.55v v l ? 5.45v undervoltage detector v u ? 4.55v v l ? 4.45v power ok figure 6. fault monitor for a single supply 10 ______________________________________________________________________________________ downloaded from: http:///
i cl7 6 6 5 m ic roproc e ssor volt a ge m onit or w it h dua l ove r/u nde rvolt a ge de t e c t ion ______________________________________________________________________________________ 11 hyst1 set1 gnd out2 set2 hyst2 out1 v+ icl7665 100k 2n4393 1m line-powered +5v input q1 1k 1 m f 5.6m 1m 2.4m 220 w 2n7000 22m 1m 1% 1.15m 1% 3v lithium cell v cc to cmos memory figure 11. battery switchover circuit figure 12. simple high/low temperature alarm hyst1 set1 out2 out1 set2 hyst2 v+ icl7665 r4 22m r5 27k r6 22m r1, 1m high- temperature limit adjustment alarm signal for driving leds, bells, etc. temperature sensor (general purpose npn transistor) r7 1.5m r2 1m low-temperature limit adjust 9v r3 470k downloaded from: http:///
_______________________scr latchup like all junction-isolated cmos circuits, the icl7665 has an inherent four-layer or scr structure that can be triggered into destructive latchup under certain co n- ditions. avoid destructive latchup by following the se precautions: 1) if either v set terminal can be driven to a voltage greater than v+ or less than ground, limit the input current to 500 a maximum. usually, an input volt- age divider resistance can be chosen to ensure the input current remains below 500 a, even when the input voltage is applied before the icl7665 v+ supply is connected. 2) limit the rate-of-rise of v+ by using a bypass capacitor near the icl7665. rate-of-rise scrs rarely occur unless: a) the battery has a low impedance?as is the case with nicd and lead acid batteries; b) the battery is connected directly to the icl7665 or is switched on via a mechanical switch with low resistance; or c) there is little or no input filter capacitance near the icl7665. in line- powered systems, the rate-of-rise is usually limited by other factors and will not cause a rate-of-rise scr action under normal circumstances. 3) limit the maximum supply vo ltage (including tran- sient spikes) to 18v. likewise, limit the maximum v olt- age on out1 and out2 to +18v and the maxi- mum voltage on hyst1 and hyst2 to 18v below v+. icl7665 microprocessor voltage monitor with dual over/undervoltage detection part temp. range pin-package icl7665ac/d 0c to +70c dice* icl7665epa+ -40c to +85c 8 plastic dip icl7665aepa+ -40c to +85c 8 plastic dip ICL7665ESA+ -40c to +85c 8 so icl7665aesa+ -40c to +85c 8 so ___________________chip topography _ordering information (continued) icl7665ipa+ -20c to +85c 8 plastic dip icl7665ija+ -20c to +85c 8 cerdip *contact factory for dice specifications. out2 v+ hyst1 0.066" (1.42mm) 0.084" (1.63mm) set1 v- set2 hyst2 out1 transistor count: 38substrate connected to v+. maxim cannot assume responsibility for use of any c ircuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 12 ____________________maxim integrated products, 160 rio robles, san jose, ca 95134 408-601-1000 ? 2015 maxim integrated products printed usa is a registered trademark of maxim integrated products. +denotes a lead(pb)-free/rohs-compliant package. downloaded from: http:///

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