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 1.0

µP Power Supply Supervisor With Battery Backup Switch

ASM690A / 692A

ASM802L / 802M

ASM805L

October 2003

General Description

The AS690A / AS692A / AS802L / AS802M / AS805L offers

complete single chip solutions for power supply monitoring and

control battery functions in microprocessor systems. Each

device implements four functions: Reset control, watchdog

monitoring,

battery-backup

switching

and

power-failure

monitoring. In addition to microprocessor reset under power-up

and power-down conditions, these devices provide battery-

backup switching to maintain control in power loss and brown-

out situations. Additional monitoring capabilities can provide an

early warning of unregulated power supply loss before the

voltage regulator drops out. The important features of these

four functions are:

•

1.6 second watchdog timer to keep microprocessor

responsive

•

power-up and power-down

•

SPDT (Single-pole, Double-throw) PMOS switch connects

•

1.25V threshold detector for power loss or general purpose

voltage monitoring

These features are pin-compatible with the industry standard

power-supply supervisors. Short-circuit and thermal protection

have also been added. The AS690A / AS802L /

AS805L

generate a reset pulse when the supply voltage drops below

4.65V and the AS692A / AS802M generate a reset below

4.40V. The ASM802L / ASM802M have power-fail accuracy to

± 2%. The ASM805L is the same as the ASM690A except that

RESET is provided instead of RESET.

Features

•

Two precision supply-voltage monitor options

•4.65V (AS690A / AS802L / AS805L)

•4.40V (AS692A / AS802M )

•

Battery-backup power switch on-chip

•

Watchdog timer: 1.6 second timeout

•

Power failure / low battery detection

•

Short circuit protection and thermal limiting

•

Small 8-pin SO package

•

No external components

•

Specified over full temperature range

Applications

•

Embedded control systems

•

Portable/Battery operated systems

•

Intelligent instruments

•

Wireless instruments

•

Wireless communication systems

•

PDAs and hand-held equipments

•

µP / µC power supply monitoring

•

Safety system

Typical Operating Circuit

Block Diagram

+

_

0.1 µF

3.6 V

Lithium

Battery

ASM690A

Regulated +5V

Unregulated DC

GND

WDI

PFO

PFI

RESET

RESET

GND

GND

NMI

I/O LINE

CMOS

RAM

Battery-Switchover Circuit

Reset

Generator

Watchdog

Timer

WDI

PFI

RESET

(RESET)

PFO

1.25V

3.5V

0.8V

1.25V

GND

1

2

3

4

5

6

7

8

|+

|+

|+

|+

-

+

-

+

-

+

-

+

ASM690A, ASM692A, ASM802L, ASM802M, (ASM805L)

Battery-Switchover Circuit

Reset

Generator

Watchdog

Timer

WDI

PFI

RESET

(RESET)

PFO

1.25V

3.5V

0.8V

1.25V

1

2

4

5

6

7

8

|+

|+

|+

|+

-

+

-

+

-

+

-

+