BQ24700_14 Datasheet, PDF (25/32 Pages) Texas Instruments – NOTEBOOK PC BATTERY CHARGE CONTROLLER

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bq24700, bq24701
NOTEBOOK PC BATTERY CHARGE CONTROLLER
AND SELECTOR WITH DPM
SLUS452B – APRIL 2001 – REVISED NOVEMBER 2002
APPLICATION INFORMATION
PWM selector switch gate drive
Because the external P-channel MOSFETs (as well as the internal MOSFETs) have a maximum gate-source
voltage limitation of 20 V, the input voltage, VCC, cannot be used directly to drive the MOSFET gate under all
input conditions. To provide safe MOSFET-gate-drive at input voltages of less than 20 V, an intermediate gate
drive voltage rail was established (VSHP). As shown in Figure 11, VSHP has a stepped profile. For VCC
voltages of less than 15 V, VSHP = 0 and the full VCC voltage is used to drive the MOSFET gate. At input
voltages of greater than 15 V, VSHP steps to approximately one-half the VCC voltage. This ensures adequate
enhancement voltage across all operating conditions.
The gate drive voltage, Vgs, vs VCC for the PWM, and ac selector P-channel MOSFETs are shown in Figure 11.
MOSFET GATE DRIVE VOLTAGE
vs
INPUT VOLTAGE
15
10
7.5
PWM
4
ACDRV
ACDRV and PWM
0
0 4 7 10
15
20
25
30
VCC – Input Voltage – V
Figure 11
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