BQ24702_16 Datasheet, PDF (15/37 Pages) Texas Instruments – MULTICHEMISTRY BATTERY CHARGER CONTROLLER

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bq24702
bq24703
SLUS553E – MAY 2003 – REVISED OCTOBER 2007
ADAPTER CURRENT LIMIT
ADAPTER CURRENT
SYSTEM CURRENT
BATTERY CHARGE CURRENT
NO
CHARGE
MAXIMUM
CHARGE CURRENT
DYNAMIC POWER
MANAGEMENT
MAXIMUM
CHARGE CURRENT
Figure 1. Dynamic Power Management
UDG-00113
ACDET OPERATION
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.
BATTERY CHARGER OPERATION
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.
PRECHARGE OPERATION
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.
Copyright © 2003–2007, Texas Instruments Incorporated
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