MIC79110 Datasheet, PDF (11/12 Pages) Micrel Semiconductor – Simple 1.2A Linear Li-Ion Battery Charger

MIC79110
Auto Top Off Charger - Application Circuit
200 ohms
R_{1 3M}
SD
GND
RSET REOC
VSENSE DEOC
VBAT ACHG
VIN
VIN
R_{2 1M}
LI-ion Battery
2kΩ
V_IN
Micrel
Top-Off-Charger with Internal Reset - Application
Circuit
SD
GND
RSET REOC
200 ohms
2kΩ
VSENSE DEOC
VBAT ACHG
R_{1 3meg}
VIN
VIN
R₂ 1meg
LI-ion Battery
V_IN
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.
Battery
charging ^{Self discharge}
4.2 V
V_{Bat min}
V_Battery
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
V_IN
R1
C_IN
R2
V_IN
V_OUT
SD
GND
V_BAT
C_OUT
Deoc trip
I_Battery
V_s
( ) ^R1
V_{Bat min}=0.975V _R2 +1
R₂=1meg
( ) ^{VBat min}
1
R₁= _0.975 -1 _R2
Vbat set (4.2V)
Vbat
4
2
Vbat low set
by divider.
3
1
SD Voltage
1 - SD not held low by active high D_EOC 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 D_EOC
open
5 - Divider voltage drops below SD threshold and
charging begins again.
July 2004
The shutdown pin on the MIC79110 can be used to automati-
cally 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 V_IN using a resistor divider. Use the
following equation to setup the maximum V_IN.
V_IN(MAX) ₌ R_{1 + 1}
V_SD
R₂
The MIC79110 can be connected to a wall wart with a rectified
DC voltage and protected from over voltages at the input.
11
M9999-072004