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BQ24702PW View Datasheet(PDF) - Texas Instruments

Part NameBQ24702PW TI
Texas Instruments TI

BQ24702PW Datasheet PDF : 32 Pages
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bq24702, bq24703
SLUS553D − MAY 2003 − REVISED JULY 2005
Programming the Thresholds
The input-referenced thresholds for battery depleted, ac detection and charge voltage are defined by
dimensioning the external dividers connected to pins BATDEP, ACDET and BATP. This calculation is simple,
and consists of assuming that when the input voltage equals the desired threshold value the voltage at the
related pin is equal to the pin internal reference voltage:
Vinput = Vpin × (1 + Kres)
Vinput = Target threshold, referenced to input signal
Vpin = Internal reference(1.196 V for BATP; 1.246 V for BATDEP, ACDET)
Kres = External resistive divider gain ( for instance: R24/R25 for BATP)
When using external dividers with high absolute value the input bias currents for those pins must be included
in the threshold calculation. On the bq24702/3 the input bias currents increase the actual value for the threshold
voltage, when compared to the values calculated using the internal references and divider gain only:
Vinput = Vpin × (1+Kres) + Vbias
The increase on the threshold voltage is given by:
Vbias = Rdiv × Ipin
Vbias = Voltage increase due to pin bias current
Rdiv = External resistor value for resistor connected from pin to input voltage
Ipin = Maximum pin leakage current
The effect of IB can be reduced if the resistor values are decreased.
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. IBAT = IADPT − ISYS). If the system plus battery charge
current exceeds the adapter current limit, as shown in Figure 1, 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 2. 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.
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The bq24702/bq24703 is a highly integrated battery charge controller and selector tailored for notebook and sub-notebook PC applications.
The bq24702/bq24703 uses dynamic power management (DPM) to minimize battery charge time by maximizing use of available wall-adapter power. This is achieved by dynamically adjusting the battery charge current based on the total system (adapter) current.
The bq24702/bq24703 uses a fixed frequency, pulse width modulator (PWM) to accurately control battery charge current and voltage. Charge current limits can be programmed from a keyboard controller DAC or by external resistor dividers from the precision 5-V, ±0.6%, externally bypassed voltage reference (VREF), supplied by the bq24702/bq24703.

● Dynamic Power Management, DPM
   Minimizes Battery Charge Time
● Integrated Selector Supports Battery
   Conditioning and Smart Battery Learn Cycle
● Zero Volt Operation
● Selector Feedback Circuit Ensures
   Break-Before-Make Transition
● ±0.4% Charge Voltage Accuracy, Suitable for
   Charging Li-Ion Cells
● ±4% Charge Current Accuracy
● 300-kHz Integrated PWM Controller for
   High-Efficiency Buck Regulation
● Depleted Battery Detection and Indication to
   Protect Battery From Over Discharge
● 20-µA Sleep Mode Current for Low Battery
● 24-Pin TSSOP Package and 5 mm × 5 mm
   QFN package (bq24703 only)

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