BQ24705 Datasheet, PDF (19/30 Pages) Texas Instruments – Host-Controlled Multi-Chemistry Battery Charger With Low Input Power Detect

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bq24705
SLUS779 – DECEMBER 2007
INPUT UNDERVOLTAGE LOCK OUT (UVLO)
The system must have a minimum 5V PVCC voltage to allow proper operation. This PVCC voltage could come
from either input adapter or battery, using a diode-OR input. When the PVCC voltage is below 5 V the bias
circuits REGN and VREF stay inactive, even with ACDET above 0.6 V.
BATTERY OVERVOLTAGE PROTECTION
The converter stops switching when BAT voltage goes above 104% of the regulation voltage. The converter will
not allow the high-side FET to turn on until the BAT voltage goes below 102% of the regulation voltage. This
allows one-cycle response to an overvoltage condition, such as when the load is removed or the battery is
disconnected. A 10-mA current sink from BAT to PGND is on only during charge, and allows discharging the
stored output-inductor energy into the output capacitors.
CHARGE OVERCURRENT PROTECTION
The charger has a secondary overcurrent protection. It monitors the charge current, and prevents the current
from exceeding 145% of regulated charge current. The high-side gate drive turns off when the overcurrent is
detected, and automatically resumes when the current falls below the overcurrent threshold.
THERMAL SHUTDOWN PROTECTION
The QFN package has low thermal impedance, which provides good thermal conduction from the silicon to the
ambient, to keep junctions temperatures low. As added level of protection, the charger converter turns off and
self-protects whenever the junction temperature exceeds the TSHUT threshold of 145°C. The charger stays off
until the junction temperature falls below 130°C.
Status Outputs (ACGOOD, DPMDET)
Two status outputs are available, and they all require external pull up resistors to pull the pins to system digital
rail for a high level.
ACGOOD open-drain output goes low under either of the two conditions:
1. ACDET is above 2.4 V
2. Adapter current is above 1.25 A using a 10-mΩ sense resistor (IADAPT voltage above 250 mV). Internally,
the AC current detect comparator looks between IADAPT and an internal 250-mV threshold. It indicates a
good adapter is connected because of valid voltage or current.
STAT open-drain output goes low when charging. A high level on STAT indicates the charger is not charging;
therefore, either, CHGEN pin is not low, or the charger is not able to charge because input voltage is still
powering up and the 700-ms delay has not finished, or because of a fault condition such as overcurrent, input
over voltage, or TSHUT overtemperature.
DPMDET open-drain output goes low when the DPM loop is active to reduce the battery charge current (after a
10-ms delay).
Copyright © 2007, Texas Instruments Incorporated
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