BQ24700 Datasheet, PDF (13/29 Pages) Texas Instruments – NOTEBOOK PC BATTERY CHARGE CONTROLLER AND SELECTOR WITH DPM

ą
bq24700, bq24701
NOTEBOOK PC BATTERY CHARGE CONTROLLER
AND SELECTOR WITH DPM
SLUS452B – APRIL 2001 – REVISED NOVEMBER 2002
APPLICATION INFORMATION
dynamic power management
The dynamic power management (DPM) feature allows a cost effective choice of an ac wall-adapter that
accommodates 90% of the system’s operating-current requirements. It minimizes battery charge time by
allocating available power to charge the battery (i.e. I_BAT = I_ADPT – I_SYS). If the system plus battery charge
current exceeds the adapter current limit, as shown in Figure 2, the DPM feature reduces the battery charge
current to maintain an overall input current consumption within user defined power capability of the wall-adapter.
As the system’s current requirements decrease, additional current can be directed to the battery, thereby
increasing battery charge current and minimizing battery charge time.
The DPM feature is inherently designed into the PWM controller by inclusion of the three control loops,
battery-charge regulation voltage, battery-charge current, and adapter-charge current, refer to Figure 3. If any
of the three user programmed limits are reached, the corresponding control loop commands the PWM controller
to reduce duty cycle, thereby reducing the battery charge current.
ADAPTER CURRENT LIMIT
ADAPTER CURRENT
SYSTEM CURRENT
BATTERY CHARGE CURRENT
NO
CHARGE
MAXIMUM
CHARGE CURRENT
DYNAMIC POWER
MANAGEMENT
MAXIMUM
CHARGE CURRENT
Figure 2. 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 1.2 V reference voltage, a loss of ADAPTER power is declared and the bq24700/bq24701 switches to
battery power as the main system power. In addition, the bq24700/bq24701 shuts down its 5-V VREF and enters
a low power sleep mode. Under normal operation with a battery present, the low impedance battery node
absorbs excess energy stored in the system capacitors (from the higher V_ADPT voltage) and quickly bring the
system voltage down to the battery voltage level. However, in conditions where the battery has been removed
or appears high impedance due to battery protector operation, the residual system energy stored in the load
capacitors due to the higher V_ADPT level is directly coupled to the SRN and SRP terminals when the battery
switch-over occurs. This presents a problem for V_ADPT voltages greater than the absolute maximum voltage
rating of the SRN and SRP pins.
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
13