Datasheet
Regulation
voltage
Precharge
Phase
Current Regulation
Phase
Voltage Regulation
Phase
Charge Current
Battery
Voltage
V
SYS
System Voltage
Linear Charge
to Maintain
Minimum
System
Voltage
V
BATSHRT
(3 V)
50mA Precharge to
Close Pack Protector
Battery FET is ON
Battery
FET
is OFF
Charge Current
Regulation
Threshold
Termination
Current
Threshold
I
BATSHRT
(3.7 V)
bq24270
bq24271
www.ti.com
SLUSB10 –JUNE 2012
Figure 3. Typical Charging Profile of bq24270 and bq24271
PWM Controller in Charge Mode
The bq24270 and bq24271 provide an integrated, fixed-frequency 1.5 MHz voltage-mode controller to power the
system and supply the charge current. The voltage loop is internally compensated and provides enough phase
margin for stable operation, allowing the use of small ceramic capacitors with low ESR. The input scheme for the
devices prevents battery discharge when the supply voltages are lower than V
BAT
. The high-side N-MOSFET
(Q1) switches to control the power delivered to the output. The DRV LDO provides a supply for the gate drive for
the low side MOSFET, while a bootstrap circuit (BST) with an external bootstrap capacitor is used to boost up
the gate drive voltage for Q1.
The input is protected by a cycle-by-cycle current limit that is sensed through the internal sense MOSFETs for
Q1. The threshold for the current limit is set to a nominal 5-A peak current. The input also uses an input current
limit that limits the current from the power source
Battery Charging Process
When the battery is deeply discharged or shorted (V
(BAT)
< V
(BATSHRT)
) the bq24270 and bq24271 apply I
BATSHRT
to close the pack protector switch and bring the battery voltage up to acceptable charging levels. During this
time, the battery FET is linearly regulated and the system output is regulated to V
SYS(REG)
. Once the battery rises
above V
(BATSHRT)
, the charge current is regulated to the value set in the I
2
C register. The battery FET is linearly
regulated to maintain the system voltage at V
SYS(REG)
. Under normal conditions, the time spent in this region is a
short percentage of the total charging time, so the linear regulation of the charge current does not affect the
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Product Folder Link(s): bq24270 bq24271