Datasheet

Regulation
voltage
Precharge
Phase
Current Regulation
Phase
Voltage Regulation
Phase
Charge Current
Battery
Voltage
System Voltage
Linear Charge
to Maintain
Minimum
System
Voltage
50 mA Precharge to
Close Pack Protector
Battery FET is ON
Battery
FET
is OFF
Charge Current
Regulation
Threshold
Termination
Current
Threshold
I
BATSHORT
V
BATSHORT
(3.0 V)
V
SYS
(3.6 V)
bq24272
SLUSB09 –JUNE 2012 www.ti.com
Figure 2. Typical Charging Profile for bq24272
PWM Controller in Charge Mode
The bq24272 provides an integrated, fixed-frequency 1.5MHz 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 very low ESR. The input scheme for the
bq24272 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 utilizes 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 bq24272 applies I
BATSHRT
for t
DETECT
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. Under normal conditions, the time spent in this region is a very short
percentage of the total charging time, so the linear regulation of the charge current does not affect the overall
charging efficiency for very long. If the die temperature does heat up, the thermal regulation circuit reduces the
charge current to maintain a die temperature less than 125°C. If the current limit for the SYS output is reached
(limited by the input current limit, or V
IN_DPM
), the SYS output drops to the V
MINSYS
output voltage. When this
happens, the current is reduced to provide the system with all the current that is needed while maintaining the
minimum system voltage. If the charge current is reduced to 0mA, pulling further current from SYS causes the
output to fall to the battery voltage and enter supplement mode (see the “Dynamic Power Path Management”
section for more details).
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