MIC79110-4.2BML datasheet(13/14 Pages) MICREL

13 / 14 page

Micrel, Inc.

MIC79110

October 2007

M9999-102507

Auto Top-Off-Charger - Application Circuit

Lithium-Ion batteries will begin to lose their charge over

time. The MIC79110 can be configured to automatically

recharge the battery if the voltage drops below a certain

voltage. This minimum voltage is set by a resistor divider

at the battery and connected to the SD pin. When the

battery voltage falls below the minimum voltage, the SD

pin is pulled low to start the normal charging process.

4.2 V

VBat min

Deoc trip

Battery

charging

IBattery

VBattery

VBat min=0.975V(

R2 +1)

R2=1meg

R1=(

VBat min

0.975 -1)

Self discharge

Vbat set (4.2V)

Vbat low set

by divider.

Vbat

SD Voltage

1. SD not held low by active high DEOC because

DEOC Comparator’s inputs do not common-mode

to ground. Divider holds SD low so part can

start.

2. SD held low by divider.

3. SD held low by active high DEOC.

4. Divider voltage above SD threshold and DEOC

open.

5. Divider voltage drops below SD threshold and

charging begins again.

Top-Off-Charger with Internal Reset - Application

Circuit

LI-ion Battery

VIN

RSET

SNS

BAT

VIN

GND

REOC

DEOC

AEOC

VIN

This circuit is similar to the auto top off charger circuit

mentioned above except that the DEOC pin is externally

triggered to restart the charging cycle. It still uses the

same resistor divider to set the minimum battery voltage

before the lithium-ion needs to be recharged.

Auto-Shutdown Using Shutdown Pin

The shutdown pin on the MIC79110 can be used to

automatically shutdown the battery charger when the

input voltage rises above a safe operating voltage. To

keep the part from heating up and entering thermal

shutdown, we can connect the shutdown pin to VIN using

a resistor divider. Use the following equation to setup the

maximum VIN.

(MAX)

The MIC79110 can be connected to a wall wart with a

rectified DC voltage and protected from over voltages at

the input.

MIC79110-4.2BML Datasheet(PDF) 13 Page - Micrel Semiconductor

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