Datasheet

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UDG-00113
NO
CHARGE
MAXIMUM
CHARGE CURRENT
DYNAMIC POWER
MANAGEMENT
MAXIMUM
CHARGE CURRENT
ADAPTER CURRENT
SYSTEM CURRENT
BATTERY CHARGE CURRENT
ADAPTER CURRENT LIMIT
ACDET OPERATION
BATTERY CHARGER OPERATION
PRECHARGE OPERATION
bq24702
bq24703
SLUS553E – MAY 2003 – REVISED OCTOBER 2007
Figure 1. Dynamic Power Management
The ACDET function senses the loss of adequate adapter power. If the voltage on ACDET drops below the
internal V
ACPRES
reference voltage, a loss of ADAPTER power is declared and the bq24702/bq24703 switches to
battery power as the main system power. In addition, the bq24702/bq24703 shuts down its 5-V VREF and enters
a low power sleep mode.
The bq24702/bq24703 fixed-frequency, PWM controller is designed to provide closed-loop control of battery
charge-current (I
CH
) based on three parameters, battery-float voltage (V
BAT
), battery-charge current, and adapter
charge current (I
ADPT
). The bq24702/bq24703 is designed primarily for control of a buck converter using a high
side P-channel MOSFET device (SW, refer to Figure 2 ).
The three control parameters are voltage programmable through resistor dividers from the bq24702/bq24703
precision 5-V reference, an external or internal precision reference, or directly via a DAC interface from a
keyboard controller.
Adapter and battery-charge current information is sensed and fed back to two transconductance ( g
m
) amplifiers
via low-value-sense resistors in series with the adapter and battery respectively. Battery voltage information is
sensed through an external resistor divider and fed back from the battery to a third g
m
amplifier.
The precharge operation must be performed using the PWM regulator. The host can set the precharge current
externally by monitoring the ALARM pin to detect a battery depleted condition and programming SRSET voltage
to obtain the desired precharge current level.
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