©2004 Fairchild Semiconductor Corporation

1

www.fairchildsemi.com

September 2004

FM1233A Rev. E

FM1233A

3-Pin µC Supervisor Circuit

General Description

The FM1233A 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 3.3V and 3.0V systems

with different tolerances.

FM1233A features a precision temperature-compensated volt-

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

and other circuits to stabilize. The reset output of FM1233A is of

open-drain active low type.

The FM1233A 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 FM1233A.

Features

■ Precision monitoring of 3.3V and lower voltage

microprocessor systems

■ Automatic restart of microprocessor after power failure

■ Reset Timeout Period Choice:

– Options AC and AD: 140ms (min)/256ms (typ)

– Option ABA: 17ms (min)/32ms (typ)

– Available on request: 64ms (typ) and 128ms (typ)

■ Internal 5kΩ pull-up resistor

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

■ Monitors external pushbutton override

■ Internal switch debounce circuitry

■ SOT23-3 package

Typical Operating Circuit

Connection Diagram

SOT23-3 Package

1

FM1233A

Controller

2

3

GND

RESET

GND

RESET

1

FM1233A

2

3