MIC79110_13 Datasheet, PDF (11/16 Pages) Micrel Semiconductor – Simple 1.2A Linear Li-ion Battery Charger

Micrel, Inc.
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:
I_RSET = (0.2/R_SET) × 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:
MIC79110
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 V_BAT > V_IN 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 R_SET pin and is constant
down to around 300mV. Since R_SET 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.
I_EOC = (0.2/R_EOC) × 1000
Eq. 2
Using a 4kΩ R_EOC resistor will set the end-of-charge
current at 50mA.
I_EOC 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 I_BAT.
• Low state indicates that the I_BAT current is higher than
the programmed current set by R_EOC.
• High state indicates that the I_BAT current is lower than
the programmed current set by R_EOC. 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.
Figure 1. MIC79110 Constant Output Voltage
September 23, 2013
11
Revision 2.1