Fairchild Semiconductor FM812J Datasheet

www.fairchildsemi.com

REV. 1.5.1 7/15/02

Preliminary Information

PRELIMINARY INFORMATION describes products that are in the design stage. Specifications may change

in any manner whatever without notice. Contact Fairchild Semiconductor for current information.

Features

• Feature

• Precision Voltage Monitor for 3V, 3.3V or 5V Power
Supplies

• 6µA Supply Current

• 140ms Minimum Reset Pulse Width

• RESET

Remains Valid with V

CC

as Low as 1.4V

• Active Low Manual Reset Input

• No External Components

• 4-Pin SOT-143 Package

Applications

• Critical Microprocessor Power Monitoring

• Portable Equipment

• Intelligent Instruments

• Computers & Printers

• Controllers

Description

The FM811/FM812 is a low cost microprocessor supervisory
circuit that asserts a reset if the power supply drops below a
designated threshold or the manual reset pin is forced low.
Several different reset thresholds are available to
accommodate systems operating at 3V, 3.3V or 5V.

The FM811 has an active low RESET

output, while the
FM812 offers an active high RESET output. The reset output
is guaranteed to remain asserted for a minimum of 140ms
after V

CC

has risen above the designated reset threshold.

The FM811/FM812 is available in a 4-pin SOT-143.

Typical Applications

FM811
FM812

µP

V

CC

V

CC

RESET

RESET
INPUT

MR

(RESET)

( ) = FM812

V

CC

FM811/812

Microprocessor Reset Circuits

FM811/812

2

REV. 1.5.1 7/15/02

Preliminary Information

Pin Assignments

Pin Definitions

Internal Block Diagram

Pin Name

Pin Number

DescriptionFM811 FM812

GND 1 1 Ground Pin

RESET

2 N/A RESET goes low if V

CC

falls below the reset threshold and remains

asserted for one reset time-out period (140ms min.) after V

CC

exceeds the

reset threshold.

RESET N/A 2 RESET goes high if V

CC

falls below the reset threshold and remains

asserted for one reset time-out period (140ms min.) after V

CC

exceeds the

reset threshold.

MR

3 3 Manual reset input. Shorting this pin to GND forces a reset. The reset will

remain asserted as long as MR is held low and for one reset time-out
period (140ms min.) after MR

goes high. This input cannot be driven by a
CMOS or TTL logic. Push-button switch is recommended to be used with
this pin. Float if unused.

V

CC

4 4 Power supply input, 3V, 3.3V, or 5V

FM811

V

CC

Top View

RESET

MR

2

4

3

FM812

V

CC

RESET

MR

GND

2

1

GND

1

4

3

4

3

Reset

Generator

2

1

–

+

Reset

Threshold (V)

V

CC

MR

RESET (FM811)
RESET (FM812)

GND