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FM1233BDS3X

3-Pin µC Supervisor Circuit

Fairchild Semiconductor 

February 2003

FM1233B

3-Pin µC Supervisor Circuit

General Description

The FM1233B is a supervisor circuit that monitors a micropro-

cessor power supply or other system voltage and issues a reset

pulse when a fault condition exists. Several different threshold

voltages are offered to accommodate 5V systems with different

tolerances.

The device features a precision temperature-compensated volt-

age reference and comparator. When VCC falls to the threshold

voltage, a RESET pulse is issued, holding the output in the

active state. When power rises above VTH, the reset remains for

approximately 250 ms to allow the system clock and other cir-

cuits to stabilize. The reset output of FM1233B is of open-drain

active low type.

The FM1233B also can monitor a switch closure on its output,

enabling it to recognize an external reset from a pushbutton

switch or a µP. In the case of a switch, the closure will be

debounced by circuitry internal to the FM1233B.

Features

s Precision monitoring of 5V and lower voltage microprocessor

systems

s VTH values of 4.62V, 4.38V and 4.12V

s Automatic restart of microprocessor after power failure

s 140ms (min) power-on RESET delay (typ.: 256ms)

s Internal 5kΩ pull-up resistor

s Other reset choices available: 32 to 128ms

s Operating Temperature -40°C to +105°C

s Monitors external pushbutton override

s Internal switch debounce circuitry

s SOT23-3 package

Typical Operating Circuit

VCC

GND

Connection Diagram

3

FM1233B

1

2

RESET

Controller

GND 1

FM1233B 3 VCC

RESET 2

SOT23-3 Package

©2002 Fairchild Semiconductor Corporation

1

FM1233B Rev. D

www.fairchildsemi.com

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