CAT8710

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Detailed Description

The CAT8710 is a space-saving, low-power, quad voltage

microprocessor supervisory circuit designed to monitor 4

voltage supplies. The CAT8710 has 2 factory preset

thresholds for monitoring standard power supply voltages of

3.3 V, 3.0 V, 2.5 V, or 1.8 V, and 2 adjustable thresholds for

monitoring voltages as low as 0.62 V.

Each internal voltage comparator has a typical hysteresis

of 0.3% with respect to its reset threshold, which improves

immunity to ambient noise without significantly reducing

threshold accuracy. CAT8710 is designed to ignore short

transients.

Applications Information

Reset Output

CAT8710 provides an extended reset signal 120 ms (typ)

in duration. The output is open drain and requires an external

pull-up resistor to an external power supply. This supply can

be less than or greater than VDD, but should not exceed

5.5 V. When the external pull−up voltage is greater than

VDD reverse current flow from the external pull−up voltage

to VDD is prevented by CAT8710’s internal circuitry.

The CAT8710 is powered by VDD, which is also a

monitored voltage. When any supply drops below its

threshold, the reset output asserts low and remains low as

long as VDD is above 1.0 V.

Figure 9. RESET Output Timing Diagram

Figure 10. Interfacing to Different Logic−Supply

Voltage

3.3 V

5 V

V3

GND

V4MON

V1MON

CAT8710

RESET

RESET

mP

V2/VDD

Adjustable Thresholds

CAT8710 allows users to create 2 custom voltage

thresholds. The threshold voltage at each adjustable input is

typically 0.62 V. Monitoring of voltages greater than 0.62 V

requires a resistor-divider network to be connected to the

circuit (Figure 11).

VIN + 0.62 V

(R1 ) R2)

R2

or, written in terms of R1:

R1 + R2 VIN

0.62 V *

1

Because the CAT8710 has a guaranteed input current of

less than 50 nA on the adjustable inputs, resistor values up

to 1000 k

W can be used for R2 with < 1% error.

Unused Inputs

Connect unused monitor inputs to a supply voltage greater

in magnitude than their specified threshold voltages; use

not connect unused monitor inputs to ground or allow them

to float.

Adding Manual Reset Capability

Figure 12 illustrates how to add manual reset to the

CAT8710. Depressing the pushbutton switch short−circuits

the analog input to ground and initiates a RESET pulse. This

technique can be used on either the V1 or V4 inputs. The

switch must be open for at least 120 ms in order to deassert

the RESET output. No external switch debounce is required.

when using long leads from the pushbutton switch to the

adjustable input.

POR

Applying power to the CAT8710 activates a POR circuit

which activates the reset output (active LOW). At power−up

POR prevents the system microprocessor from starting to

operate with insufficient voltage and prior to stabilization of

the clock oscillator. It ensures that operation is precluded

until internal registers are properly loaded, FPGA’s have

downloaded their configuration data. The reset signal

remains active until all monitored power supplies have risen

above their minimum preset voltage levels.

Power−Supply Bypassing

All monitored inputs are immune to short supply

transients. For applications where higher immunity is

required, connect a 0.1

mF bypass capacitor from each input

pin to ground very close to CAT8710’s package.