ASM1232LP/LPS

Alliance Semiconductor

2575 Augustine Drive . Santa Clara, CA 95054 . Tel: 408.855.4900 . Fax: 408.855.4999 . www.alsc.com

Notice: The information in this document is subject to change without notice

January 2005

rev 1.5

5V µP Power Supply Monitor and Reset Circuit

General Description

The ASM1232LP/LPS is a fully integrated microprocessor

supervisor. It can halt and restart a “hung-up” microprocessor,

restart a microprocessor after a power failure. It has a

watchdog timer and external reset override.

A

precision

temperature-compensated

reference

and

selectable tolerance limits, both RESET and RESET become

signals remain active for an additional 250ms minimum,

allowing the power supply and system microprocessor to

stabilize. The trip point tolerance signal, TOL, selects the trip

level tolerance to be either 5% or 10%.

Each device has both a push-pull, active HIGH reset output

and an open drain active LOW reset output. A debounced

manual reset input, PBRST, activates the reset outputs for a

minimum period of 250ms.

There is a watchdog timer to stop and restart a microprocessor

that is “hung-up”. The watchdog timeouts periods are

selectable: 150ms, 610ms and 1200ms. If the ST input is not

strobed LOW before the time-out period expires, a reset is

generated.

Devices are available in 8-pin DIP, 16-pin SO and compact 8-

pin MicroSO packages.

Key Features

•

5V supply monitor

•

Selectable watchdog period

•

Debounce manual push-button reset input

•

Precision temperature-compensated voltage reference

and comparator.

•

Power-up, power-down and brown out detection

•

250ms minimum reset time

•

Active LOW open drain reset output and active HIGH

push-pull output

•

Selectable trip point tolerance: 5% or 10%

•

Low-cost surface mount packages: 8-pin/16-pin SO, 8-pin

DIP and 8-pin Micro SO packages

•

Wide operating temperature -40°C to +85°C (N suffixed

devices)

Applications

•

Microprocessor Systems

•

Computers

•

Controllers

•

Portable Equipment

•

Intelligent Instuments

•

Automotive Systems

Typical Operating Circuit

Block Diagram

ASM1232LP/LPS

ST

RESET

GND

TD

TOL

I/O

RESET

µP

10k

Ω

+5V

Tolerance Selection

Reference

Push Button

Voltage Sense

Watchdog Transition

Reset &

Debounce

Comparators

Detector

Watchdog Timer

+

-

RESET

RESET

PBRST

ST

TD

TOL

GND

40k

Ω

ASM1232LP/LPS