January 2006

1

MIC2779

MIC2779

Micrel, Inc.

MIC2779

Voltage Monitor with Adjustable Hysteresis

General Description

The MIC2779 is a voltage monitor—uniquely designed to

detect two separate voltage thresholds—combined with a

delay generator and logic. It is designed for monitoring the

battery supply of portable digital systems, particularly PDAs,

pagers, and cellular telephones.

High- and low-voltage thresholds can be adjusted inde-

pendently, allowing for wide hysteresis. Voltage detection

thresholds are accurate to 2%.

If the battery voltage falls below the low-voltage threshold,

the output /RST or RST is asserted and latched, preventing

system operation until the battery is replaced or recharged.

Internallogicpreventstheoutputfromchatteringduetobattery

recovery or load removal. The output is asserted for 140ms

(minimum) when a fresh battery is inserted. For applications

requiring open-drain output, see MIC2778/MIC833.

The IC’s power supply input is separate from the detector

inputs, allowing the MIC2779 to be powered from a down-

stream supply, such a boost converter. Supply current is

extremely low (1µA, typical), making it ideal for portable

applications.

A high-precision 1% grade is available. The MIC2779 is sup-

plied in Micrel’s IttyBitty™ 5-pin SOT-23-5 package.

Typical Application

HTH

/ RST

VDD

LTH

GND

MIC2779L

604k

1%

56k

1%

340k

1%

EN

OUT

IN

B YP

GND

MIC5207-3.0BM5

Li-Ion

Cell

470pF

3.0V

4.7µF

Cellular Telephone Battery Monitor

Features

• Optimized for PDAs, cellular telephones, pagers,

and other battery-powered devices

• Independently adjustable high- and

low-voltage thresholds

• Internal logic prevents battery-voltage-fluctuation chatter

• High ±2% voltage threshold accuracy; 1% available

• Built in 140ms (minimum) delay deglitches output

• Extremely low 1µA typical supply current

• For applications requiring open-drain output, see

MIC2778/MIC833

• Immune to brief power supply transients

• 5-pin SOT-23 package

Applications

• PDAs

• Pagers

• Cordless phones

• Consumer electronics

• Embedded controllers

• Personal electronics

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

IttyBitty™ is a trademark of Micrel, Inc.