BQ24700 Datasheet, PDF (17/29 Pages) Texas Instruments – NOTEBOOK PC BATTERY CHARGE CONTROLLER AND SELECTOR WITH DPM

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bq24700, bq24701
NOTEBOOK PC BATTERY CHARGE CONTROLLER
AND SELECTOR WITH DPM
SLUS452B – APRIL 2001 – REVISED NOVEMBER 2002
APPLICATION INFORMATION
I _CH(avg)
I _CH
PWM
VS
VC
CLK
Figure 5. Typical PWM Waveforms in a Buck Converter (Including Startup)
UDG–00115
setting the battery charge regulation voltage
The battery charge regulation voltage is programmed through the BATSET pin, if the internal 1.25-V 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 6).
The battery voltage is fed back to the g_m amplifier through a resistor divider network. The battery charge
regulation voltage can be defined as:
VBATTERY
+
(R1
)
R2) VBATSET
R2
V
(1)
The overall accuracy of the battery charge regulation voltage is a function of the bypassed 5-V reference voltage
tolerance as well as the tolerances on R1 and R2. The precision voltage reference has a 0.5% tolerance making
it suitable for the tight battery voltage requirements of Li-ion batteries. Tolerance resistors of 0.1% are
recommended for R1 and R2 as well as any resistors used to set BATSET.
The bq24700/bq24701 provides the capability of using an internal precision voltage reference (1.25 Vdc)
through the use of a multiplexing scheme, refer to Figure 6, on the BATSET pin. When BATSET voltage is less
than 0.25 V, an internal 1.25-V, 0.5% reference is switched in and the BATSET pin is switched out from the g_m
amplifier input. When the BATSET voltage is greater than 0.25 V, the BATSET pin voltage is switched in to the
input of the g_m amplifier and the 1.25 V voltage reference is switched out.
NOTE:The minumum recommended BATSET is 1.0 V, if BATSET is used to set the voltage loop.
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
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