REV. A

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a

ADM9690

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 2000

Power Supply and Watchdog Timer

Monitoring Circuit

FUNCTIONAL BLOCK DIAGRAM

WATCHDOG

TRANSITION

DETECTOR

OSC SEL1

OSC SEL2

RESET(2)

TIMER

RESET(1)

TIMER

4.31V

ADM9690

RESET(1)

RESET(2)

WATCHDOG

INPUT (WDI)

GND

WATCHDOG

TIMEBASE

FEATURES

Precision Voltage Monitor (4.31 V)

Watchdog Timeout Monitor

Selectable Watchdog Timeout—0.75 ms, 1.5 ms,

12.5 ms, 25 ms

Two RESET Outputs

APPLICATIONS

Microprocessor Systems

Computers

Printers

Controllers

Intelligent Instruments

GENERAL DESCRIPTION

The ADM9690 contains a voltage monitoring comparator and a

watchdog timer monitor. It is designed to monitor the 5 V

power supply to a microprocessor and the microprocessor opera-

tion via a watchdog function.

The voltage monitoring comparator monitors the voltage on

power-fail, two reset signals are generated. Both reset signals go

active (low) simultaneously. They will remain active while

60 ms (RESET(2

)) after V

old. RESET(1) is intended to provide a power-on reset signal

for the

µP while RESET(2) is used to hold additional circuitry

in a reset state until the

µP has regained control following a

power-up. The voltage monitoring circuitry remains operational

The watchdog timer monitoring circuit is designed to monitor

the activity on the WDI input. This input is normally connected

to an output line on the

µP. Its function is to check that the

microprocessor has not stalled in an infinite loop. If there is a

period of inactivity for the watchdog timeout period, both reset

outputs are activated. As above, RESET(1

) remains low for

50 ms while RESET(2) remains low for an additional 10 ms.

The watchdog timer is restarted when RESET(1

) goes inactive.

The actual watchdog timeout period is adjustable using two

select inputs SEL1 and SEL2.

The ADM9690 is available in an 8-lead SOIC package. It is

specified over the industrial temperature range.