ASM1832

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

rev 1.5

3.3V µP Power Supply Monitor and Reset Circuit

February 2005

General Description

The ASM1832 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. RESET and RESET outputs are

push-pull.

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 10% or 20%.

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 PDIP, 8-pin SO and compact 8-

pin MicroSO packages.

Key Features

•

3.3V supply monitor

•

Push-pull output

•

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 and HIGH reset signal

•

Selectable trip point tolerance: 10% or 20%

•

Low-cost 8-pin DIP/SO and 8-pin Micro SO packages

•

Wide operating temperature -40°C to +85°C

Applications

•

Microprocessor systems

•

Computers

•

Controllers

•

Portable instruments

•

Automotive systems

Typical Operating Circuit

Block Diagram

Tolerance Selection

Reference

Push Button

Debounce

Voltage Sense

Comparator

Reset &

Watchdog Timer

Watchdog

Transition Detector

+

-

TOL

PBRST

TD

ST

RESET

RESET

40K

Ω

GND

ASM1832

ST

RESET

RESET

I/O

µP

ASM1832

GND

TOL

TD

3.3V