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

ASM811, ASM812

4 Pin µP Voltage Supervisor with Manual Reset

October 2003

rev 1.0

Reset Output Operation

In µP / µC systems it is important to have the processor and

the system begin operation from a known state. A reset

output to a processor is provided to prevent improper

operation during power supply sequencing or low voltage

brown-out conditions.

The ASM811/812 are designed to monitor the system power

supply voltages and issue a reset signal when the levels are

out of range. RESET outputs are guaranteed to be active for

internal timer keeps RESET active for the reset timeout

period, after which RESET becomes inactive (HIGH for the

reset threshold, RESET automatically becomes active.

Alternatively, external circuitry or an operator can initiate this

condition using the Manual Reset (MR) pin. MR can be left

open if it is not used. MR can be driven by TTL/CMOS logic

or even an external switch.

To ensure logic inputs connected to the ASM811 RESET pin

down resistor at RESET is needed. The value is not critical.

A 100k

Application Information

Negative VCC Transients

Typically short duration transients of 100mV amplitude and

20µs duration do not cause a false RESET. A 0.1µF capacitor

Bidirectional Reset Pin Interfacing

The ASM811/812 can interface with µP / µC bi-directional

reset pins by connecting a 4.7k

Ω resistor in series with the

ASM811/812 reset output and the µP/µC bi-directional reset

input pin.

Power supply

BUF

Buffered

RESET

ASM811

GND

GND

RESET

RESET

Input

µC or µP

4.7kΩ

Bi-directional I/O Pin

Figure 4: Bi-directional Reset Pin Interface

MR

Power Supply

ASM811

RESET

GND

100kΩ

Power Supply

ASM812

RESET

GND

MR

MR

100kΩ

0V

5V

5V

0V

5V

0V

5V

0V

MR

RESET

RESET

ASM811

ASM812

Figure 1: Reset Timing and Manual Reset (MR)