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19-0001; Rev 2; 8/97
Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection
_______________General Description
The ICL7665 warns microprocessors (Ps) of overvoltage and undervoltage conditions. It draws a typical operating current of only 3A. The trip points and hysteresis of the two voltage detectors are individually programmed via external resistors to any voltage greater than 1.3V. The ICL7665 will operate from any supply voltage in the 1.6V to 16V range, while monitoring voltages from 1.3V to several hundred volts. The Maxim ICL7665A is an improved version with a 2%-accurate V SET1 threshold and guaranteed performance over temperature. The 3A quiescent current of the ICL7665 makes it ideal for voltage monitoring in battery-powered systems. In both battery- and line-powered systems, the unique combination of a reference, two comparators, and hysteresis outputs reduces the size and component count of many circuits.
____________________________Features
o P Over/Undervoltage Warning o Improved Second Source o Dual Comparator with Precision Internal Reference o 3A Operating Current o 2% Threshold Accuracy (ICL7665A) o 1.6V to 16V Supply Voltage Range o On-Board Hysteresis Outputs o Externally Programmable Trip Points o Monolithic, Low-Power CMOS Design
ICL7665
______________Ordering Information
PART ICL7665CPA TEMP. RANGE 0C to +70C PIN-PACKAGE 8 Plastic DIP
________________________Applications
P Voltage Monitoring Low-Battery Detection Power-Fail and Brownout Detection Battery Backup Switching Power-Supply Fault Monitoring Over/Undervoltage Protection High/Low Temperature, Pressure, Voltage Alarms
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 Ordering Information continued on last page.
_________________Pin Configurations
TOP VIEW
OUT1 1 2 8 7 V+ OUT2 SET2 HYST2
__________Typical Operating Circuit
VIN1 OVERVOLTAGE DETECTION V+ 8 V+ OUT2 VIN2 UNDERVOLTAGE DETECTION NMI
HYST1
SET1 3 GND 4
ICL7665
6 5
1 OUT1
7
DIP/SO
8
V+ (CASE)
7
ICL7665
3 SET1 GND 4 SET2 6
OUT1
1
OUT2
HYST1
2 3
ICL7665
5 4
6
SET2 HYST2
SET1
GND
SIMPLE THRESHOLD DETECTOR
TO-99 1
________________________________________________________________ Maxim Integrated Products
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468.
Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection ICL7665
ABSOLUTE MAXIMUM RATINGS
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)........................................(GND - 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 (TA = +70C) Plastic DIP (derate 9.09mW/C above +70C) ............727mW SO (derate 5.88mW/C above +70C) ........................471mW CERDIP (derate 8.00mW/C above +70C) ................640mW TO-99 (derate 6.67mW/C above +70C) ...................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
Note 1: Due to the SCR structure inherent in the CMOS process used to fabricate these devices, connecting any terminal to voltages 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 operating 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 first. If this is not possible, currents into inputs and/or outputs must be limited to 0.5mA and voltages must not exceed those defined above.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V+ = 5V, TA = +25C, unless otherwise noted.) PARAMETER SYMBOL ICL7665 Operating Supply Voltage V+ ICL7665A ICL7665B CONDITIONS TA = +25C TA = TMIN to TMIN TA = TMIN to TMIN TA = +25C TA = TMIN to TMIN ICL7665, TA = +25C; ICL7665A, TA = TMIN to TMAX ICL7665B, TA = +25C V+ = 2V V+ = 9V V+ = 15V V+ = 2V V+ = 9V VSET1 VSET2 VSET1 VSET2 VSET1 VSET2 1.150 1.200 1.275 1.225 1.250 1.215 MIN 1.6 1.8 2.0 1.6 1.8 2.5 2.6 2.9 2.5 2.6 1.300 1.300 1.300 1.300 1.300 1.300 100 ROUT1, ROUT2, RHYST1, RHYST2 = 1M 0.004 TYP MAX 16 16 16 10 10 10 10 15 10 10 1.450 1.400 1.325 1.375 1.350 1.385 ppm/C %/V V A V UNITS
Supply Current
I+
GND VSET1, VSET2 V+, all outputs open circuit
ICL7665, ICL7665B, TA = +25C Input Trip Voltage VSET ICL7665A, TA = +25C ICL7665A, TA = TMIN to TMAX VSET Tempco Supply Voltage Sensitivity of VSET1, VSET2
2
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Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 5V, TA = +25C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS All grades, VSET = 0V or VSET 2V, TA = +25C Output Leakage Current IOLK, IHLK ICL7665, ICL7665A, V+ = 15V, TA = TMIN to TMAX ICL7665B, V+ = 9V, TA = TMIN to TMAX OUT1, OUT2 HYST1, HSYT2 OUT1, OUT2 HYST1, HSYT2 OUT1, OUT2 HYST1, HSYT2 ICL7665, ICL7665B: V+ = 2V ICL7665A: V+ = 2V VOUT1 Saturation Voltage VSET1 = 2V, IOUT1 = 2mA All grades: V+ = 5V ICL7665, ICL7665A: V+ = 15V ICL7665B: V+ = 9V All grades: V+ = 2V VHYST1 Saturation Voltage VSET1 = 2V, IHYST1 = -0.5mA All grades: V+ = 5V ICL7665, ICL665A: V+ = 15V ICL7665B: V+ = 9V All grades: V+ = 2V VOUT2 Saturation Voltage VSET2 = 0V, IOUT2 = 2mA VSET2 = 2V, IHYST2 = -0.2mA VHYST2 Saturation Voltage All grades: V+ = 5V ICL7665, ICL665A: V+ = 15V ICL7665B: V+ = 9V All grades: V+ = 2V All grades: V+ = 5V VSET2 = 2V, IHYST2 = -0.5mA ICL7665: V+ = 15V ICL7665A: V+ = 15V ICL7665B: V+ = 9V VSET Input Leakage Current VSET Input Change for Complete Output Change Difference in Trip Voltage Output/Hysteresis Difference ISET VSET VSET1- VSET2 GND VSET V+ ROUT = 4.7k, RHYST = 20k, VOUTLO = 1% V+, VOUTHI = 99% V+ ROUT, RHYST = 1M ROUT, RHYST = 1M 0.20 0.20 0.10 0.06 0.06 -0.15 -0.05 -0.02 -0.02 0.20 0.15 0.11 0.11 -0.25 -0.43 -0.35 -0.35 -0.35 0.01 0.30 0.20 0.25 -0.30 -0.15 -0.10 -0.15 0.50 0.30 0.25 0.30 -0.80 -1.00 -0.80 -1.00 -1.00 10 nA V V V V MIN TYP 10 -10 MAX 200 -100 2000 nA -500 2000 -500 0.50 UNITS
ICL7665
0.1
mV
5 0.1
50
mV mV
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3
Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection ICL7665
AC OPERATING CHARACTERISTICS
(V+ = 5V, TA = +25C, unless otherwise noted.) PARAMETER Output Delay Time, Input Going High SYMBOL tSO1d tSH1d tSO2d tSH2d tSO1d Output Delay Time, Input Going Low tSH1d tSO2d tSH2d tO1r Output Rise Times tO2r tH1r tH2r tO1f Output Fall Times tO2f tH1f tH2f VSET switched between 1.0V and 1.6V, ROUT = 4.7k, CL = 12pF, RHYST = 20k VSET switched between 1.0V and 1.6V, ROUT = 4.7k, CL = 12pF, RHYST = 20k VSET switched from 1.6V to 1.0V, ROUT = 4.7k, CL = 12pF, RHYST = 20k VSET switched from 1.0V to 1.6V, ROUT = 4.7k, CL = 12pF, RHYST = 20k CONDITIONS MIN TYP 85 90 55 55 75 80 60 60 0.6 0.8 7.5 0.7 0.6 0.7 4.0 1.8 s s s s MAX UNITS
_______________________________________________________Switching Waveforms
1.6V INPUT VSET1,VSET2 t SO1d t SO1d OUT1 t O1f HYST1 t SH1d t H1r t SO2d OUT2 t O2r HYST2 t SH2d t SH2d t H2r t H2f t O2f GND V+ (5V) GND t SO2d t SH1d t H1f V+ (5V) t O1r GND V+ (5V) GND V+ (5V) 1.0V
4
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Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection
__________________________________________Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
SUPPLY CURRENT AS A FUNCTION OF SUPPLY VOLTAGE
ICL7665-02 ICL7665-01
ICL7665
OUT1 SATURATION VOLTAGE AS A FUNCTION OF OUTPUT CURRENT
2.0 V+ = 2V VOLTAGE SATURATION (V) 1.5 V+ = 5V V+ = 9V 1.0 V+ = 15V 5.0 4.5 4.0 SUPPLY CURRENT (A)
SUPPLY CURRENT AS A FUNCTION OF AMBIENT TEMPERATURE
4.5 4.0 0V VSET1, VSET2 V+ V+ = 15V V+ = 9V
ICL7665-03
0V VSET1, VSET2 V+
5.0
TA = -20C TA = +25C TA = +70C
3.0 2.5 2.0 1.5 1.0 0.5
SUPPLY CURRENT (A)
3.5
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0
0.5
V+ = 2V
0 0 5 10 IOUT OUT1 (mA) 15 20
0 0 2 4 6 8 10 12 SUPPLY VOLTAGE (V) 14 16
-20
0 20 40 AMBIENT TEMPERATURE (C)
60
HYST1 OUTPUT SATURATION VOLTAGE vs. HYST1 OUTPUT CURRENT
ICL7665-04
HYST2 OUTPUT SATURATION VOLTAGE vs. HYST2 OUTPUT CURRENT
HYST2 OUTPUT SATURATION VOLTAGE (V)
ICL7665-05
OUT2 SATURATION VOLTAGE AS A FUNCTION OF OUTPUT CURRENT
ICL7665-06
0 HYST1 OUTPUT SATURATION VOLTAGE (V)
0
2.0
-0.4 V+ = 15V -0.8 V+ = 9V -1.2 V+ = 5V V+ = 2V
-1 VOLTAGE SATURATION (V) V+ = 15V V+ = 9V V+ = 5V
1.5
-2
1.0
V+ = 2V V+ = 5V V+ = 9V V+ = 15V
-3 V+ = 2V
0.5
-1.6
-4
-2.0 -20 -16 -12 -8 -4 0 HYST1 OUTPUT CURRENT (mA)
-5 -5 -4 -3 -2 -1 0 HYST2 OUTPUT CURRENT (mA)
0 0 5 10 IOUT OUT2 (mA) 15 20
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5
Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection ICL7665
V+ 4.7k OUT1 HYST1
1 2 INPUT 1.6V 1.0V 3 4
OUT1 HYST1 SET1 GND
V+
8 7 6 5 20k
4.7k OUT2
ICL7665
OUT2 SET2 HSYT2
HSYT2 20k 12pF 12pF 12pF 12pF
Figure 1. Test Circuit
_______________Detailed Description
As shown in the block diagram of Figure 2, the Maxim ICL7665 combines a 1.3V reference with two comparators, two open-drain N-channel outputs, and two open-drain P-channel hysteresis outputs. The reference and comparator are very low-power linear CMOS circuits, with a total operating current of 10A maximum, 3A typical. The N-channel outputs can sink greater than 10mA, but are unable to source any current. These outputs are suitable for wire-OR connections and are capable of driving TTL inputs when an external pull-up resistor is added. The ICL7665 Truth Table is shown in Table 1. OUT1 is an inverting output; all other outputs are noninverting. 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 connected to ground. Both OUT1 and OUT2 can drive at least one TTL load with a VOL of 0.4V.
V+ SET1 HYST1
OUT1
1.3V BANDGAP REFERENCE
TO V+
HYST2
SET2
OUT2
Table 1. ICL7665 Truth Table
INPUT* VSET1 > 1.3V VSET1 < 1.3V VSET2 > 1.3V VSET2 < 1.3V OUTPUT OUT1 = ON = LOW OUT1 = OFF = HI OUT2 = OFF = HI OUT2 = ON = LOW HYSTERESIS HYST1 = ON = HI
HYST1 = OFF = LOW
Figure 2. Block Diagram
HYST2 = ON = HI
HYST2 = OFF = LOW
OUT1 is an inverting output; all others are noninverting. OUT1 and OUT2 are open-drain, N-channel current sinks. HYST1 and HYST2 are open-drain, P-channel current sinks.
In spite of the very low operating current, the ICL7665 has a typical propagation delay of only 75s. Since the comparator input bias current and the output leakages are very low, high-impedance external resistors can be used. This design feature minimizes both the total supply current used and loading on the voltage source that is being monitored.
* See Electrical Characteristics
6 _______________________________________________________________________________________
Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection ICL7665
VIN1
OUT1 R21
V+
OUT2
VIN2
VIN1
V+
VIN2
OUT1 R22 R21 R31 SET1 R12 R11
OUT2 R22
ICL7665
SET1 R11 SET2
ICL7665
HYST1 HYST2 SET2
R32
R12
V+ OUT1 OUT1 VIN1 VTRIP1 OUT2 VIN2 VTRIP2 0V VIN2 VL1 VIN1 OUT2 VL2 VU2 VU1 0V V+
Figure 3. Simple Threshold Detector
Figure 4. Threshold Detector with Hysteresis
Basic Over/Undervoltage Detection Circuits
Figures 3, 4, and 5 show the three basic voltage detection circuits. The simplest circuit, depicted in Figure 3, does not have any hysteresis. The comparator trip-point formulas can easily be derived by observing that the comparator changes state when the VSET input is 1.3V. The external resistors form a voltage divider that attenuates the input signal. This ensures that the VSET terminal is at 1.3V when the input voltage is at the desired comparator trip point. Since the bias current of the comparator is only a fraction of a nanoamp, the current in the voltage divider can be less than one microamp without losing accuracy due to bias currents. The ICL7665A has a 2% threshold accuracy at +25C, and a typical temperature coefficient of 100ppm/C including comparator offset drift, eliminating the need for external potentiometers in most applications. Figure 4 adds another resistor to each voltage detector. This third resistor supplies current from the HYST output whenever the VSET input is above the 1.3V threshold. As the formulas show, this hysteresis resistor affects only the lower trip point. Hysteresis (defined as
the difference between the upper and lower trip points) keeps noise or small variations in the input signal from repeatedly switching the output when the input signal remains near the trip point for a long period of time. The third basic circuit, Figure 5, is suitable only when the voltage to be detected is also the power-supply voltage for the ICL7665. This circuit has the advantage that all of the current flowing through the input divider resistors flows through the hysteresis resistor. This allows the use of higher-value resistors, without hysteresis output leakage 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 VSET / R11. R11 can typically be in the range of 10k to 10M. 2) Calculate R21 based on R11 and the desired trip point:
VTRIP - VSET VTRIP - 1.3V R21 = R11 -------------- = R11 ------------ VSET 1.3V
(
)(
)
7
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Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection ICL7665
VIN
R31 HYST1 R21 V+ HYST2
R32
Figure 5 1) Select a value for R11, usually between 10k and 10M. 2) Calculate R21: VL - VSET R21 = R11 ------------ VSET 3) Calculate R31:
ICL7665
SET1 SET2
R22
(
)
VL - 1.3V = R11 ---------- 1.3
(
)
OVERVOLTAGE
OUT1 R11 GND OUT2
UNDERVOLTAGE
R12
OUT1 VL1 VU1 OUT2 VL2 VU2 VIN
VU - VL R31 = R11 ---------- VSET 4) As in the other circuits, all three resistor values may be scaled up or down in value without changing VU and VL. VU and VL depend only on the ratio of the three resistors, if the absolute values are such that the hysteresis output resistance and the leakage currents of the VSET input and hysteresis output can be ignored.
(
)
__________Applications Information
Fault Monitor for a Single Supply
Figure 6 shows a typical over/undervoltage fault monitor for a single supply. In this case, the upper trip points (controlling OUT1) are centered on 5.5V, with 100mV of hysteresis (VU = 5.55V, VL = 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 signal.
Figure 5. Threshold Detector, VIN = V+
Figure 4 1) Choose a resistor value for R11. Typical values are in the 10k to 10M range. 2) Calculate R21 for the desired upper trip point, VU, using the formula: VU - VSET VU - 1.3V R21 = R11 ------------ = R11 ---------- VSET 1.3V
Multiple-Supply Fault Monitor
The ICL7665 can simultaneously monitor several power supplies, as shown in Figure 7. The easiest way to calculate the resistor values is to note that when the VSET 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, R21A and R21B are chosen so that the current through the two resistors is equal. Note that, since the voltage at the ICL7665 VSET input depends on the voltage of both supplies being monitored, there will be some interaction between the lowvoltage trip points for the two supplies. In this example, OUT1 will go low when either supply is 10% below nominal (assuming the other supply is at the nominal voltage), or when both supplies are 5% or more below their nominal voltage. R31 sets the hysteresis, in this case, to about 43mV at the 5V supply or 170mV at the 15V supply. The second section of ICL7665 can be used to detect overvoltage or, as shown in Figure 7, can be used to detect the absence of negative supplies. Note that the trip points for OUT2 depend on both the voltages of the negative power supplies and the actual voltage of the +5V supply.
(
)
(
)
3) Calculate R31 for the desired amount of hysteresis: (R21) (V+ - 1.3V) (R21) (V+ - VSET) R31 = ------------------ = ------------------ VU - VL VU - VL or, if V+ = VIN: (R21) (VL - VSET) (R21) (VL - 1.3V) R31 = ------------------ = ------------------ VU - VL VU - VL 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 output's resistance, and the current through R31 is much higher than the HYST output's leakage current. Normally, R31 will be in the 100k to 22M range. Multiplying or dividing all three resistors by the same factor will not affect the trip voltages.
8
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Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection
Combination Low-Battery Warning and Low-Battery Disconnect
Nickel cadmium (NiCd) batteries are excellent rechargeable power sources for portable equipment, but care must be taken to ensure that NiCd batteries are not damaged by overdischarge. Specifically, a NiCd battery should not be discharged to the point where the polarity of the lowest-capacity cell is reversed, and that cell is reverse charged by the higher-capacity cells. This reverse charging will dramatically reduce the life of a NiCd 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 is ordinarily 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 battery, the load should be disconnected when the battery voltage is 1V x (N - 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 load is disconnected, 800mV of hysteresis is used to prevent repeated on/off cycling. exceeds 10.2V. When the 110V AC power-line voltage is either interrupted or reduced so that the peak voltage 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 R1 x C1 determines the delay time before the power-fail warning signal is activated, in this case 42ms or 212 line cycles. Optional components R2, R3 and Q1 add hysteresis by increasing the peak secondary voltage required to discharge C1 once the power-fail warning is active.
ICL7665
Battery Switchover Circuit
The circuit in Figure 11 performs two functions: switching 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, Q1, 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 saturated. 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 course). Another possible use for the second section of the ICL7665 is the detection of the input voltage falling below 4.5V. This signal could then be used to prevent the microprocessor from writing spurious data to the CMOS memory while its power-supply voltage is outside its guaranteed operating range.
Power-Fail Warning and Power-Up/Power-Down Reset
Figure 9 illustrates a power-fail warning circuit that monitors raw DC input voltage to the 7805 three-terminal 5V regulator. The power-fail warning signal goes 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 7805 decays at a rate of IOUT / C (in this case, 200mV/ms). Since the 7805 will continue to provide a 5V output at 1A until VIN 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 increased, 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 activate a battery-backup system.
Simple High/Low Temperature Alarm
The circuit in Figure 12 is a simple high/low temperature 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 multiplier whose output voltage is determined by the Vbe of the transistor and the position of R1's wiper arm. The voltage at the top of R1 will have a temperature coefficient of approximately -5mV/C. R1 is set so that the voltage at VSET2 equals the VSET2 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 VSET1 is 1.3V when the NPN transistor's temperature reaches the low-temperature limit.
AC Power-Fail and Brownout Detector
By monitoring the secondary of the transformer, the circuit in Figure 10 performs the same power-failure warning function as Figure 9. With a normal 110V AC input to the transformer, OUT1 will discharge C1 every 16.7ms when the peak transformer secondary voltage
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9
Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection ICL7665
+5V SUPPLY R21A 274k HYST2 7.5M 5% SET2 OUT2 UNDERVOLTAGE 100k DETECTOR VU 4.55V VL 4.45V 249k R21B 1.02M +15V +5V R31 22M HYST2 V+ HYST1 22M 100k +5V
HYST1 324k 13M 5% SET1 OVERVOLTAGE DETECTOR VU 5.55V VL 5.45V 100k OUT1
V+
ICL7665
SET2 SET1 OUT1 +5V -5V -15V 301k 787k OUT2
ICL7665
R11 49.9k
POWER OK
POWER OK
Figure 6. Fault Monitor for a Single Supply
Figure 7. Multiple-Supply Fault Monitor
R31 V+ HYST1 R21 SET1 R11 OUT1 GND OUT2 HYST2
R32
1M V+ OUT1
100 OUT2 SENSE
+5V, 1A OUTPUT
ICL7665
SET2
R22
ICL7663
SHDN R12 GND SET
LOW-BATTERY SHUTDOWN
LOW-BATTERY WARNING
Figure 8. Low-Battery Warning and Low-Battery Disconnect
UNREGULATED DC INPUT
4700F
7805 5V REGULATOR 470F
5V, 1A OUTPUT BACK-UP BATTERY
10VAC 60Hz
5V, 1A 20V CENTER TAPPED TRANS 4700F 7805 5V REGULATOR
+5V V+ HYST1 HYST2 R1
V+ HYST1 5.6M 715k HYST2 22M 681k
ICL7665
SET1 SET2 OUT2
ICL7665
SET1 130k OUT1 OUT2 SET2 1M
2.2M
RESET OR WRITE ENABLE
100k
R2 1M R3 1M
OUT1
C1
Q1
POWER-FAIL WARNING
POWER-FAIL WARNING
Figure 9. Power-Fail Warning and Power-Up/Power-Down Reset
10
Figure 10. AC Power-Fail and Brownout Detector
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Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection ICL7665
LINE-POWERED +5V INPUT
100k 1k Q1 1F
VCC TO CMOS MEMORY
2N7000 1M
2N4393
OUT1 HYST1 5.6M
V+ HYST2 22M 1.15M 1% 3V LITHIUM CELL
ICL7665
2.4M 1M GND 220 OUT2 SET1 SET2 1M 1%
Figure 11. Battery Switchover Circuit
9V
V+ TEMPERATURE SENSOR (GENERAL PURPOSE NPN TRANSISTOR) HYST2 R3 470k R4 22M SET2 R1, 1M HIGHTEMPERATURE LIMIT ADJUSTMENT R5 27k OUT2 OUT1 HYST1 R6 22M SET1 R7 1.5M R2 1M LOW-TEMPERATURE LIMIT ADJUST
ICL7665
ALARM SIGNAL FOR DRIVING LEDS, BELLS, ETC.
Figure 12. Simple High/Low Temperature Alarm
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11
Microprocessor Voltage Monitor with Dual Over/Undervoltage Detection ICL7665
_______________________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 conditions. Avoid destructive latchup by following these precautions: 1) If either VSET terminal can be driven to a voltage greater than V+ or less than ground, limit the input current to 500A maximum. Usually, an input voltage divider resistance can be chosen to ensure the input current remains below 500A, 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 linepowered 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 voltage (including transient spikes) to 18V. Likewise, limit the maximum voltage on OUT1 and OUT2 to +18V and the maximum voltage on HYST1 and HYST2 to 18V below V+.
___________________Chip Topography
V+ OUT2
0.066" (1.42mm) OUT1 SET2 HYST2 HYST1 SET1 0.084" (1.63mm) V-
TRANSISTOR COUNT: 38 SUBSTRATE CONNECTED TO V+.
_Ordering Information (continued)
PART ICL7665CTV ICL7665ACTV ICL7665BCTV ICL7665AC/D ICL7665IPA ICL7665IJA ICL7665EPA ICL7665AEPA ICL7665ESA ICL7665AESA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C -20C to +85C -20C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 8 TO-99 8 TO-99 8 TO-99 Dice* 8 Plastic DIP 8 CERDIP 8 Plastic DIP 8 Plastic DIP 8 SO 8 SO
*Contact factory for dice specifications.
Maxim cannot assume responsibility for use of any circuitry 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, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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