Datasheet

bq24270
bq24271
www.ti.com SLUSB10 –JUNE 2012
Input Voltage Based DPM
During normal charging process, if the input power source is not able to support the programmed or default
charging current, the supply voltage deceases. Once the supply drops to V
IN_DPM
(default 4.2 V), the input
current limit is reduced down to prevent further supply droop. When the IC enters this mode, the charge
current is lower than the set value and the DPM_STATUS bit is set (Bit 5 in Register 05H). This feature
ensures IC compatibility with adapters with different current capabilities without a hardware change. Figure 8
shows the V
IN-DPM
behavior to a current limited source. In this figure, the input source has a 750 mA current
limit and the charging is set to 750 mA. The SYS load is then increased to 1.2 A.
Figure 8. bq24270 V
IN-DPM
Bad Source Detection
When a source is connected to USB, the bq24270 and bq24271 run a Bad Source Detection procedure to
determine if the source is strong enough to provide some current to charge the battery. A current sink is
turned on (30 mA) for 32 ms. If the source is valid after the 32 ms (V
(BAD_SOURCE)
< V
(USB)
< V
(OVP)
), the buck
converter starts up and normal operation continues. If the supply voltage falls below V
(BAD_SOURCE)
during the
detection, the current sink shuts off for 2s and then retries. The detection circuits retries, a single 128 μs
pulse is sent on the STAT and INT outputs, and the STATx and FAULT_x bits of the status registers and the
battery/supply status registers are updated in the I
2
C. The detection circuits retries continuously until either a
new source is connected to the other input or a valid source is detected after the detection time. If during
normal operation the source falls to V
(BAD_SOURCE)
, the devices turn off the PWM converter, turn on the
battery FET and BGATE, send a single 128 μs pulse on the STAT and INT outputs, and the STATx and
FAULT_x bits of the status registers and the battery/supply status registers are updated in the I
2
C. Once a
good source is detected, the STATx and FAULT_x bits are cleared and the devices return to normal
operation
Input Overvoltage Protection
The bq24270 and bq24271 provide overvoltage protection on the input that protects downstream circuitry.
The built-in input overvoltage protection to protect the devices and other components against damage from
overvoltage on the input supply (Voltage from V
(USB)
or V
IN
to PGND). During normal operation, if V
(USB)
>
V
(OVP)
, the devices turn off the PWM converter, turns the battery FET and BGATE on, sends a single 128 μs
pulse is sent on the STAT and INT outputs and the STATx and FAULT_x bits of the status registers and the
battery and supply status registers are updated in the I
2
C. Once the OVP fault is removed, the STATx and
FAULT_x bits are cleared and the devices return to normal operation.
Copyright © 2012, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Link(s): bq24270 bq24271