January 2005
rev 1.5
ASM1232LP/LPS
5V µP Power Supply Monitor and Reset Circuit
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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)
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
Applications
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Microprocessor Systems
Computers
Controllers
Portable Equipment
Intelligent Instuments
Automotive Systems
comparator circuits monitor the 5V, V
CC
input voltage status.
During power-up or when the V
CC
power supply falls outside
selectable tolerance limits, both RESET and RESET become
active. When V
CC
rises above the threshold voltage, the reset
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.
Typical Operating Circuit
+5V
ASM1232LP/LPS
ST
RESET
GND
TD
TOL
10kΩ
I/O
µP
RESET
Block Diagram
ASM1232LP/LPS
V
CC
TOL
Tolerance Selection
+
Reference
V
CC
40kΩ
Key Features
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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%
RESET
-
RESET
PBRST
TD
Push Button
Debounce
Voltage Sense
Comparators
Watchdog Transition
Detector
Reset &
Watchdog Timer
ST
GND
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
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
