_______________General Description

The ICL7665 warns microprocessors (

Ps) of overvolt-

age and undervoltage conditions. It draws a typical
operating current of only 3µA. The trip points and hys-
teresis of the two voltage detectors are individually pro-
grammed 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 volt-
ages 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 3µA quiescent current of the ICL7665 makes it
ideal for voltage monitoring in battery-powered sys-
tems. In both battery- and line-powered systems, the
unique combination of a reference, two comparators,
and hysteresis outputs reduces the size and compo-
nent count of many circuits.

________________________Applications

µP 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

____________________________Features

µP Over/Undervoltage Warning

Improved Second Source

Dual Comparator with Precision Internal Reference

3µA Operating Current

2% 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

OUT2

SET2

HYST2

GND

SET1

HYST1

OUT1

ICL7665

DIP/SO

TOP VIEW

ICL7665

V+ (CASE)

HYST2

SET2

OUT2

OUT1

HYST1

SET1

TO-99

GND

V+

_________________Pin Configurations

ICL7665

OUT1

OUT2

SET2

SET1

V+

IN2

IN1

V+

GND

OVERVOLTAGE

DETECTION

UNDERVOLTAGE

DETECTION

SIMPLE THRESHOLD DETECTOR

NMI

__________Typical Operating Circuit

19-0001; Rev 2; 8/97

PART

TEMP. RANGE

PIN-PACKAGE

ICL7665CPA

0°C to +70°C

8 Plastic DIP

ICL7665ACPA

0°C to +70°C

8 Plastic DIP

ICL7665BCPA

0°C to +70°C

8 Plastic DIP

ICL7665CSA

0°C to +70°C

8 SO

ICL7665ACSA

0°C to +70°C

8 SO

ICL7665BCSA

0°C to +70°C

8 SO

ICL7665CJA

0°C to +70°C

8 CERDIP

ICL7665ACJA

0°C to +70°C

8 CERDIP

ICL7665BCJA

0°C to +70°C

8 CERDIP

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.

ICL7665

Microprocessor Voltage Monitor with
Dual Over/Undervoltage Detection

_______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V+ = 5V, T

= +25°C, unless otherwise noted.)

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.

Note 1:

Due to the SCR structure inherent in the CMOS process 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 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 possi-
ble, currents into inputs and/or outputs must be limited 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)........................................(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 (T

= +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_ _.......................................................0°C to +70°C
ICL7665I_ _ .....................................................-20°C to +85°C
ICL7665E_ _ ....................................................-40°C to +85°C

Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

Operating Supply Voltage

V+

ICL7665

= +25°C

1.6

= T

MIN

to T

MIN

1.8

ICL7665A

= T

MIN

to T

MIN

2.0

ICL7665B

= +25°C

1.6

Input Trip Voltage

SET

ICL7665, ICL7665B, T

= +25°C

SET1

1.150

1.300

1.450

SET2

1.200

1.300

1.400

ICL7665A, T

= +25°C

SET1

1.275

1.300

1.325

SET2

1.225

1.300

1.375

ICL7665A, T

= T

MIN

to T

MAX

SET1

1.250

1.300

1.350

SET2

1.215

1.300

1.385

SET

Tempco

100

ppm/°C

OUT1

, R

OUT2

, R

HYST1

, R

HYST2

= 1M

0.004

%/V

Supply Current

I+

GND

SET1,

SET2

V+,

all outputs open
circuit

V+ = 2V

2.5

V+ = 9V

2.6

V+ = 15V

2.9

ICL7665B,
T

= +25°C

V+ = 2V

2.5

V+ = 9V

2.6

= T

MIN

to T

MIN

1.8

ICL7665,
T

= +25°C;

ICL7665A,
T

= T

MIN

to T

MAX

Supply Voltage Sensitivity
of V

SET1

, V

SET2

ICL7665

Microprocessor Voltage Monitor with

Dual Over/Undervoltage Detection

_______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(V+ = 5V, T

= +25°C, unless otherwise noted.)

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Output Leakage Current

OLK

HLK

All grades, V

SET

= 0V or

SET

2V, T

= +25°C

OUT1, OUT2

200

HYST1, HSYT2

-10

-100

OUT1, OUT2

2000

HYST1, HSYT2

-500

ICL7665B, V+ = 9V,
T

= T

MIN

to T

MAX

OUT1, OUT2

2000

HYST1, HSYT2

-500

OUT1

Saturation

Voltage

SET1

= 2V,

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

OUT2

Saturation

Voltage

SET2

= 0V,

OUT2

= 2mA

All grades: V+ = 2V

0.20

0.50

All grades: V+ = 5V

0.15

0.30

ICL7665, ICL665A: V+ = 15V

0.11

0.25

ICL7665B: V+ = 9V

0.11

0.30

HYST2

Saturation

Voltage

All grades: V+ = 2V

-0.25

-0.80

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

SET

GND

SET

V+

±0.01

±10

SET

0.1

SET1

SET2

±5

±50

±0.1

SYMBOL

HYST1

Saturation

Voltage

SET1

= 2V,

HYST1

= -0.5mA

ICL7665, ICL7665A,
V+ = 15V,
T

= T

MIN

to T

MAX

SET2

= 2V,

HYST2

= -0.2mA

SET2

= 2V,

HYST2

= -0.5mA

SET

Input Leakage

Current

OUT

, R

HYST

= 1M

OUT

, R

HYST

= 1M

OUT

= 4.7k

, R

HYST

= 20k

OUT

LO = 1% V+, V

OUT

HI = 99% V+

SET

Input Change for

Complete Output
Change

Difference in Trip
Voltage

Output/Hysteresis
Difference

ICL7665

Microprocessor Voltage Monitor with
Dual Over/Undervoltage Detection

_______________________________________________________________________________________

AC OPERATING CHARACTERISTICS

(V+ = 5V, T

= +25°C, unless otherwise noted.)

SET

switched between 1.0V and 1.6V,

OUT

= 4.7k

, C

= 12pF,

HYST

= 20k

µs

1.8

H2f

Output Fall Times

4.0

H1f

0.7

O2f

0.6

O1f

SET

switched between 1.0V and 1.6V,

OUT

= 4.7k

, C

= 12pF,

HYST

= 20k

µs

0.7

H2r

Output Rise Times

7.5

H1r

0.8

O2r

0.6

O1r

SET

switched from 1.6V to 1.0V,

OUT

= 4.7k

, C

= 12pF,

HYST

= 20k

µs

SH2d

Output Delay Time,
Input Going Low

SO2d

SH1d

SO1d

SET

switched from 1.0V to 1.6V,

OUT

= 4.7k

, C

= 12pF,

HYST

= 20k

CONDITIONS

µs

SH2d

Output Delay Time,
Input Going High

SO2d

SH1d

SO1d

UNITS

MIN

TYP

MAX

SYMBOL

PARAMETER

INPUT

OUT1

HYST1

OUT2

HYST2

O1f

SO1d

H1r

SO2d

SH2d

O2r

O2f

SH2d

O1r

1.6V

1.0V

V+ (5V)

GND

V+ (5V)

GND

V+ (5V)

GND

V+ (5V)

GND

SET1,

SET2

SH1d

H2r

H2f

SO2d

SH1d

H1f

SO1d

_______________________________________________________Switching Waveforms

ICL7665

Microprocessor Voltage Monitor with

Dual Over/Undervoltage Detection

_______________________________________________________________________________________

2.0

OUT1 SATURATION VOLTAGE AS A

FUNCTION OF OUTPUT CURRENT

0.5

1.5

ICL7665-01

OUT

OUT1 (mA)

VOLTAGE SATURATION (V)

1.0

V+ = 2V

V+ = 9V

V+ = 15V

V+ = 5V

SUPPLY CURRENT AS A

FUNCTION OF SUPPLY VOLTAGE

SUPPLY CURRENT (

SUPPLY VOLTAGE (V)

ICL7665-02

0.5

1.0

= +25°C

= +70°C

SET1

, V

SET2

V+

1.5

2.0

2.5

3.0

3.5

5.0

4.5

4.0

= -20°C

SUPPLY CURRENT AS A

FUNCTION OF AMBIENT TEMPERATURE

-20

AMBIENT TEMPERATURE (°C)

ICL7665-03

SUPPLY CURRENT (

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

SET1

, V

SET2

V+

-2.0

-1.6

-1.2

-0.8

-0.4

-20

-16

-12

-8

-4

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

-5

-4

-3

-2

-1

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

OUT2 SATURATION VOLTAGE AS A

FUNCTION OF OUTPUT CURRENT

VOLTAGE SATURATION (V)

OUT

OUT2 (mA)

ICL7665-06

V+ = 2V

V+ = 5V

V+ = 9V

V+ = 15V

__________________________________________Typical Operating Characteristics

= +25°C, unless otherwise noted.)

ICL7665

_______________Detailed Description

As shown in the block diagram of Figure 2, the Maxim
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

A maxi-

mum, 3

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 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 connect-
ed to ground. Both OUT1 and OUT2 can drive at least
one TTL load with a V

of 0.4V.

In spite of the very low operating current, the ICL7665
has a typical propagation delay of only 75

s. 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 sup-
ply current used and loading on the voltage source that
is being monitored.

Microprocessor Voltage Monitor with
Dual Over/Undervoltage Detection

_______________________________________________________________________________________

Figure 1. Test Circuit

HYST2 = OFF = LOW

OUT2 = ON = LOW

SET2

< 1.3V

HYST2 = ON = HI

OUT2 = OFF = HI

SET2

> 1.3V

HYST1 = OFF = LOW

OUT1 = OFF = HI

SET1

< 1.3V

HYST1 = ON = HI

OUT1 = ON = LOW

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

ICL7665

OUT1

HYST1

SET1

GND

V+

OUT2

SET2

HSYT2

12pF

OUT1

HYST1

OUT2

HSYT2

4.7k

V+

1.6V

1.0V

INPUT

20k

* See Electrical Characteristics

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.

Basic Over/Undervoltage

Detection Circuits

Figures 3, 4, and 5 show the three basic voltage detec-
tion 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 V

SET

input is 1.3V. The exter-

nal resistors form a voltage divider that attenuates the
input signal. This ensures that the V

SET

terminal is at

1.3V when the input voltage is at the desired compara-
tor trip point. Since the bias current of the comparator
is only a fraction of a nanoamp, the current in the volt-
age divider can be less than one microamp without los-
ing accuracy due to bias currents. The ICL7665A has a
2% threshold accuracy at +25°C, and a typical temper-
ature coefficient of 100ppm/°C including comparator
offset drift, eliminating the need for external poten-
tiometers in most applications.

Figure 4 adds another resistor to each voltage detector.
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 (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 V

SET

/ R11. R11 can typically be in the

range of 10k

to 10M

2) Calculate R21 based on R11 and the desired trip

point:

TRIP

SET

TRIP

1.3V

R21 = R11

(

--------------

)

= R11

(

------------

)

SET

1.3V

ICL7665

Microprocessor Voltage Monitor with

Dual Over/Undervoltage Detection

_______________________________________________________________________________________

Figure 3. Simple Threshold Detector

Figure 4. Threshold Detector with Hysteresis

ICL7665

OUT1

OUT2

SET2

SET1

R21

R11

R22

R12

IN1

V+

IN2

OUT1

IN1

TRIP1

TRIP2

OUT2

IN2

ICL7665

OUT1

OUT2

SET2

SET1

R21

R11

R22

R12

IN1

V+

IN2

HYST1

HYST2

R31

R32

V+

OUT1

V+

OUT2

IN1

IN2

ICL7665

Microprocessor Voltage Monitor with
Dual Over/Undervoltage Detection

_______________________________________________________________________________________

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, V

using the formula:

- V

SET

1.3V

R21 = R11

(

------------

)

= R11

(

----------

)

SET

1.3V

3) Calculate R31 for the desired amount of hysteresis:

(R21) (V+ V

SET

)

(R21) (V+ 1.3V)

R31 = ------------------ = ------------------

or, if V+ = V

(R21) (V

SET

)

(R21) (V

1.3V)

R31 = ------------------ = ------------------

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.

Figure 5

1) Select a value for R11, usually between 10k

and

10M

2) Calculate R21:

SET

1.3V

R21 = R11

(

------------

)

= R11

(

----------

)

SET

1.3

3) Calculate R31:

R31 = R11

(

----------

)

SET

4) As in the other circuits, all three resistor values may

be scaled up or down in value without changing V

and V

. V

and V

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 V

SET

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 (con-
trolling OUT1) are centered on 5.5V, with 100mV of hys-
teresis (V

= 5.55V, V

= 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.

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 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, R21A 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 the low-
voltage 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.

Figure 5. Threshold Detector, V

= V+

ICL7665

OUT1

OUT2

SET2

SET1

R21

R11

HYST1

HYST2

OUT1

OUT2

V+

GND

OVERVOLTAGE

UNDERVOLTAGE

R31

R32

R22

R12

ICL7665

Microprocessor Voltage Monitor with

Dual Over/Undervoltage Detection

_______________________________________________________________________________________

Combination Low-Battery Warning and

Low-Battery Disconnect

Nickel cadmium (NiCd) batteries are excellent recharge-
able 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 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 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.

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-termi-
nal 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 I

OUT

/ C (in this case, 200mV/ms).

Since the 7805 will continue to provide a 5V output at
1A until V

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 acti-
vate a battery-backup system.

AC Power-Fail and Brownout Detector

By monitoring the secondary of the transformer, the cir-
cuit in Figure 10 performs the same power-failure warn-
ing 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

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 2

line cycles.

Optional components R2, R3 and Q1 add hysteresis by
increasing the peak secondary voltage required to dis-
charge C1 once the power-fail warning is active.

Battery Switchover Circuit

The circuit in Figure 11 performs two functions: switch-
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, 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 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 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 out-
side its guaranteed operating range.

Simple High/Low Temperature Alarm

The circuit in Figure 12 is a simple high/low tempera-
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 multi-
plier 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 coeffi-
cient of approximately -5mV/°C. R1 is set so that the
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 transistor's temperature reaches the low-tempera-
ture limit.

ICL7665

Microprocessor Voltage Monitor with
Dual Over/Undervoltage Detection

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+

OUT1

OUT2

SHDN

SENSE

ICL7663

ICL7665

GND

LOW-BATTERY WARNING

LOW-BATTERY SHUTDOWN

+5V, 1A
OUTPUT

R31

OUT1

SET

R21

R11

R32

R22

R12

100

Figure 8. Low-Battery Warning and Low-Battery Disconnect

Figure 7. Multiple-Supply Fault Monitor

HYST1

SET1

HYST2

SET2

ICL7665

V+

UNREGULATED

DC INPUT

BACK-UP

BATTERY

RESET

WRITE

ENABLE

POWER-FAIL WARNING

4700µF

470µF

2.2M

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

R2
1M

681k

+5V

POWER-FAIL

WARNING

100k

5V, 1A

Figure 9. Power-Fail Warning and Power-Up/Power-Down Reset

Figure 10. AC Power-Fail and Brownout Detector

ICL7665

OUT1

OUT2

SET2

SET1

+5V SUPPLY

HYST1

HYST2

V+

13M

7.5M
5%

249k

324k

100k

OVERVOLTAGE

DETECTOR

5.55V

5.45V

UNDERVOLTAGE

DETECTOR
V

4.55V

4.45V

POWER OK

Figure 6. Fault Monitor for a Single Supply

______________________________________________________________________________________

_______________________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 con-
ditions. Avoid destructive latchup by following these
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 voltage (including tran-

sient spikes) to 18V. Likewise, limit the maximum volt-
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

0°C to +70°C

Dice*

ICL7665EPA

-40°C to +85°C

8 Plastic DIP

ICL7665AEPA

-40°C to +85°C

8 Plastic DIP

ICL7665ESA

-40°C to +85°C

8 SO

ICL7665AESA

-40°C to +85°C

8 SO

___________________Chip Topography

_Ordering Information (continued)

ICL7665IPA

-20°C to +85°C

8 Plastic DIP

ICL7665IJA

-20°C to +85°C

8 CERDIP

*Contact factory for dice specifications.

OUT2

V+

HYST1

0.066"

(1.42mm)

0.084"

(1.63mm)

SET1

V-

SET2

HYST2

OUT1

ICL7665CTV

0°C to +70°C

8 TO-99

ICL7665ACTV

0°C to +70°C

8 TO-99

ICL7665BCTV

0°C to +70°C

8 TO-99

TRANSISTOR COUNT: 38

SUBSTRATE CONNECTED TO V+.

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.

____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Printed USA

is a registered trademark of Maxim Integrated Products.

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ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: ICL7665AC