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
October 2003
rev 1.0 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
comparator circuits monitor the 5V, VCC input voltage status.
During power-up or when the VCC power supply falls outside
selectable tolerance limits, both RESET and RESET become
active. When VCC 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 1.200ms. 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/EMA suf-
fixed devices)
Applications
• Microproessor 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
10kΩ
+5V
Tolerance Selection
Reference
Push Button
Voltage Sense
Watchdog Transition
Reset &
Debounce
Comparators
Detector
Watchdog Timer
+
-RESET
RESET
PBRST
ST
TD
TOL
VCC
GND
40kΩ
VCC
ASM1232LP/LPS