January 2005

1

M9999-011405

MIC2778

Micrel

MIC2778

Voltage Monitor with Adjustable Hysteresis

General Description

The MIC2778 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) is asserted and latched, preventing system

operation until the battery is replaced or recharged. Internal

logic prevents the output from chattering due to battery

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

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

not requiring built-in delay, see MIC841.

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

inputs, allowing the MIC2778 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 MIC2778 is sup-

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

Typical Application

HTH

R ST

VDD

LTH

GND

MIC2778

604k

1%

56k

1%

340k

1%

E N

OUT

IN

B Y P

GND

MIC5207-3.0BM5

100k

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 not requiring built-in delay, see MIC841

• Immune to brief power supply transients

• 5-lead 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.

Ordering Information

Part Number

Accurary

Temperature Range

Package

Standard

Marking

Pb-Free

Marking

MIC2778-2BM5

UFB

MIC2778-2YM5

UFB*

2%

-40°C to +85°C

SOT-23-5

MIC2778-1BM5

UFA

MIC2778-1YM5

UFA*

1%

-40°C to +85°C

SOT-23-5

* Underscore indicates a Pb-Free part.