MIC79110YML datasheet(11/16 Pages) MICREL

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Micrel, Inc.

MIC79110

September 23, 2013

Revision 2.1

Application Information

Detailed Description

The MIC79110 forms a complete charger for 1-cell

lithium-ion batteries. It includes precision voltage control

(0.75% over temperature) to optimize both cell

performance and cycle life. All are compatible with

common 4.2V lithium-ion chemistries. Voltages other

than 4.2V can be obtained with the adjustable version.

Other features include current limit, end-of-charge ﬂag,

and end-of-charge current limit using an external resistor.

The shutdown pin enables low quiescent current when

not charging.

Current-Limit Mode

MIC79110 features an internal current limit that is set by

the RSET pin with a resistor-to-ground. The maximum

current is calculated by Equation 1:

IRSET = (0.2/RSET) × 1000

Eq. 1

Using a 167Ω RSET resistor will achieve the maximum

current limit for the MIC79110 at 1.2 amperes.

End-of-Charge

REOC pin is connected to a resistor-to-ground. This

resistor is used to set the end of charge current for the

lithium-ion battery as in Equation 2:

IEOC = (0.2/REOC) × 1000

Eq. 2

Using a 4kΩ REOC resistor will set the end-of-charge

current at 50mA.

IEOC should be set at 10% of the battery’s rated current.

Digital End-of-Charge Output

This pin is the output of an open drain. When tied high to

the supply using a resistor, the output will toggle high or

low depending on the output current of IBAT.

•

Low state indicates that the IBAT current is higher than

the programmed current set by REOC.

•

High state indicates that the IBAT current is lower than

the programmed current set by REOC. The output goes

high impedance indicating end-of-charge.

Analog End-Of-Charge Output

The ACHG pin provides a small current that is

proportional to the charge current. The ratio is set at

1/1000th of the output current.

Shutdown

The SD pin serves as a logic input (active low) to enable

the charger.

Built-in hysteresis for the shutdown pin is 50mV over

temperature.

Reverse Polarity Protection

In the event that VBAT > VIN and the shutdown pin is active

low, there is reverse battery current protection built in.

The current is limited to less than 10µA over temperature.

Constant Output Voltage/Current Charging

The MIC79110 features constant voltage and constant

current output to correctly charge lithium-ion batteries.

The constant voltage is either 4.2V or adjustable. The

constant current is set by the RSET pin and is constant

down to around 300mV. Since RSET can be set below

500mA, the minimum output current is set at 500mA for

output voltages below 100mV. This minimum voltage

starts the charging process in lithium-ion batteries. If the

output current is too low, the battery will not begin

charge.

Figure 1. MIC79110 Constant Output Voltage

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