BQ24740_14 Datasheet, PDF (22/33 Pages) Texas Instruments – Host-Controlled Multi-Chemistry Battery Charger

bq24740
SLUS736C – DECEMBER 2006 – REVISED MARCH 2009............................................................................................................................................... www.ti.com
ACDET
ACVDET
Comparator
+ ^AC_VGOOD
2.4 V -
t_dg
rising
700 ms
AC_VGOOD_DG
To Control Logic
EXT_PWR_DG
EXTPWR
ACP
Adaptor
Current Sense
1 kΩ
Amplifier
+
ACIDET
ACN
-
Comparator
250 mV
(1.25 A) ^-
AC_IGOOD
+
20 kΩ
IADAPT
Error
Amplifier
Disable
-
+
IADAPT
OUTPUT
BUFFER
20 xV(ACP-ACN)
IADAPT
Disable
IADAPT
LPREF
LPMD
Comparator
+
-
Program Hysteresis of comparator externally
by putting a resistor in feedback from LPMD pin to LPREF pin.
LOPWR_DET
Figure 30. EXTPWR, LPREF and LPMD Logic
LPMD
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 over-current 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 155°C. The charger stays off
until the junction temperature falls below 135°C.
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