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BQ24702PW View Datasheet(PDF) - Texas Instruments

Part NameBQ24702PW TI
Texas Instruments TI
DescriptionMULTICHEMISTRY BATTERY CHARGER CONTROLLER AND SYSTEM POWER SELECTOR


BQ24702PW Datasheet PDF : 32 Pages
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bq24702, bq24703
SLUS553D − MAY 2003 − REVISED JULY 2005
Softstart
Softstart is provided to ensure an orderly start-up when the PWM is enabled. When the PWM controller is
disabled (ENABLE = Low), the 100-µA current source pullup is disabled and the COMP pin is actively pulled
down to GND. Disabling the 100-µA pullup reduces current drain when the PWM is disabled. When the
bq24702/bq24703 PWM is enabled (ENABLE = High), the COMP pin is released and the 100-µA pullup is
enabled (refer to Figure 2). The voltage on the COMP pin increases as the pullup charges the external
compensation network connected to the COMP pin. As the voltage on the COMP pin increases the PWM duty
cycle increases linearly as shown in Figure 3.
PERCENT DUTY CYCLE
vs
COMPENSATION VOLTAGE
100
90
80
70
60
50
40
30
20
10
0
1.2
1.7
2.2
2.7
3.2
VCOMP − Compensation Voltage − V
Figure 3
As any one of the three controlling loops approaches the programmed limit, the gm amplifier begins to shunt
current away from the COMP pin. The rate of voltage rise on the COMP pin slows due to the decrease in total
current out of the pin, decreasing the rate of duty cycle increase. When the loop has reached the programmed
limit the gm amplifier shunts the entire bias current (100 µA) and the duty cycle remains fixed. If any of the control
parameters tries to exceed the programmed limit, the gm amplifier shunts additional current from the COMP pin,
further reducing the PWM duty cycle until the offending parameter is brought into check.
Setting the Battery Charge Regulation Voltage
The battery charge regulation voltage is programmed through the BATSET pin, if the internal precision
reference is not used. The BATSET input is a high-impedance input that is driven by either a keyboard controller
DAC or via a resistor divider from a precision reference (see Figure 4).
The battery voltage is fed back to the gm amplifier through a resistor divider network. The battery charge
regulation voltage can be defined as:
VBATTERY
+
(R1
)
R2)
R2
VBATSET
V ) IBATP
R1
(1)
where IBATP = input bias current for pin BATP
18
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DESCRIPTION
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.

FEATURES
● 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
   Drain
● 24-Pin TSSOP Package and 5 mm × 5 mm
   QFN package (bq24703 only)

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