BQ24740_07 Datasheet, PDF (21/32 Pages) Texas Instruments – Host-controlled Multi-chemistry Battery Charger with Low Input Power Detect

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bq24740
SLUS736 – DECEMBER 2006
INPUT UNDER VOLTAGE 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.
INPUT CURRENT LOW-POWER MODE DETECTION
In order to optimize the system performance, the HOST keeps an eye on the adapter current. Once the adapter
current is above threshold set via LPREF, LPMD pin sends signal to HOST. The signal alarms the host that
input power has exceeded the programmed limit, allowing the host to throttle back system power by reducing
clock frequency, lowering rail voltages, or disabling certain parts of the system. The LPMD pin is an open-drain
output. Connect a pull-up resistor to LPMD. The output is logic HI when the IADAPT output voltage (IADAPT =
20 x V_ACP-ACN) is lower than the LPREF input voltage. The LPREF threshold is set by an external resistor divider
using VREF. A hysteresis can be programmed by a positive feedback resistor from LPMD pin to the LPREF pin.
ACDET
ACDET
Comparator
+
2.4 V -
ACDET_DET
t_dg ^ACDET_DG
rising
700 ms
TO ACDET
Logic
ACP
ACN
1 kW
20 kW
Adaptor
Current Sense
Amplifier
+
-
IADAPT Error
Amplifier
Disable
LOIAC
Comparator
250 mV -
LOIAC_DET
+
-
+
IADAPT
Disable
EXT_PWR_DG
EXTPWR
IADAPT
LPREF
Program Hysteresis of comparator
by putting a resistor in feedback
from LPMD pin to LPREF pin.
LOPWRMODE
Comparator
+
LOPWR_DET
-
Figure 28. EXTPWR, LPREF and LPMD Logic
LPMD
BATTERY OVER-VOLTAGE 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 OVER-CURRENT PROTECTION
The charger has a secondary over-current 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 over-current is
detected, and automatically resumes when the current falls below the over-current threshold.
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