Micrel, Inc.

MIC79110

September 23, 2013

13

Revision 2.1

Figure 4. Auto Top-Off Charger Application

Figure 5. Charging Description

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.

Figure 6. Top-Off Charger with Internal Reset −

Application Circuit

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.

Figure 7. 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 Equation 3 to setup the maximum

VIN:

(

)

1

2

R

1

R

V

MAX

VIN

SD

+

=

Eq. 3

The MIC79110 can be connected to a wall wart with a

rectified DC voltage and protected from over voltages at

the input.