ADM9690 データシートの表示（PDF） - Analog Devices

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ADM9690

Power Supply and Watchdog Timer Monitoring Circuit

Analog Devices 

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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

Power Supply and Watchdog Timer

Monitoring Circuit

ADM9690

FUNCTIONAL BLOCK DIAGRAM

VCC

VMON

4.31V

ADM9690

OSC SEL1

OSC SEL2

WATCHDOG

TIMEBASE

WATCHDOG

INPUT (WDI)

WATCHDOG

TRANSITION

DETECTOR

RESET(1)

TIMER

RESET(2)

TIMER

GND

RESET(1)

RESET(2)

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

VMON. If it drops outside tolerance, as will happen during a

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

active (low) simultaneously. They will remain active while

VMON is below the threshold, and for 50 ms (RESET(1)) or

60 ms (RESET(2)) after VMON climbs above the reset thresh-

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

with VCC as low as 2 V.

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.

REV. A

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties

which may result from its use. No license is granted by implication or

otherwise under any patent or patent rights of Analog Devices.

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

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