BQ24700_14 Datasheet, PDF (22/32 Pages) Texas Instruments – NOTEBOOK PC BATTERY CHARGE CONTROLLER

bq24700, bq24701
ą
NOTEBOOK PC BATTERY CHARGE CONTROLLER
AND SELECTOR WITH DPM
SLUS452B – APRIL 2001 – REVISED NOVEMBER 2002
APPLICATION INFORMATION
selector operation
The bq24700/bq24701 allows the host controller to manually select the battery as the system’s main power
source, without having to remove adapter power. This allows battery conditioning through smart battery learn
cycles. In addition, the bq24700/bq24701 supports autonomous supply selection during fault conditions on
either supply. The selector function uses low R_DS(on) P-channel MOSFETs for reduced voltage drops and longer
battery run times. Note: Selection of battery power whether manual or automatic results in the suspension of
battery charging.
ADAPTER SELECT SWITCH
ADAPTER
INPUT
(bq24700) 24 ^ACDRV
BATTERY
SELECTOR _BATDRV
CONTROL 23
(bq24700)
PWM
BATTERY
CHARGER
SYSTEM
LOAD
BATTERY
BAT
SELECT
SWITCH
UDG–00119
Figure 9. Selector Control Switches
autonomous selection operation
Adapter voltage information is sensed at the ACDET pin via a resistor divider from the adapter input (refer to
ACDET operation section). The voltage on the ACDET pin is compared to an internally fixed threshold. An
ACDET voltage less than the set threshold is considered as a loss of adapter power regardless of the actual
voltage at the adapter input. Information concerning the status of adapter power is fed back to the host controller
through ACPRES. The presence of adapter power is indicated by ACPRES being set high. A loss of adapter
power is indicated by ACPRES going low regardless of which power source is powering the system. During a
loss of adapter power, the bq24700/bq24701 obtains operating power from the battery through the body diode
of the P-channel battery select MOSFET. Under a loss of adapter power, ACPRES (normally high) goes low,
if adapter power is selected to power the system, the bq24700/bq24701 automatically switches over to battery
power by commanding ACDRV high and BATDRV low and ALARM goes high. During the switch transition
period, battery power is supplied to the load via the body diode of the battery select P-channel MOSFET. When
adapter power is restored, the bq24700/bq24701 configures the selector switches according to the state of
signals; ACSEL, and ACPRES. If the ACSEL pin is left high when ac power is restored, the bq24700/bq24701
automatically switches back to ac power and the ALARM pin goes low. To remain on battery power after ac
power is restored, the ACSEL pin must be brought low.
Conversely, if the battery is removed while the system is running on battery power and adapter power is present,
the bq24700/bq24701 automatically switches over to adapter power by commanding BATDRV high and
ACDRV low. Note: For the bq24700 any fault condition that results in the selector MOSFET switches not
matching their programmed states is indicated by the ALARM pin going high. Please refer to Battery Depletion
Detection Section for more information on the ALARM discrete.
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