AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
VIN
C1+
C1
1µF
D1
RB*
D2
RB*
D3
RB*
D4
RB*
C1-
VOUT
C2+
CIN
COUT
C2
VBATTERY
AAT3131
1µF
1µF
1µF
C2-
D1
D2
D3
EN/SET
EN/SET
GND
D4
D5
D6
RB*
RB*
*In some applications, white LED forward voltages (VF) can vary significantly. Ballast resistors between the LED cathodes and ground are recommended
for balancing the forward voltage differences. The ballast resistor value may be approximated by the following equation:
VSOURCE - VF
=
RB
IF
Figure 2: AAT3131 Driving Two Groups of Paralleled White LEDs
(e.g., main LCD and sub-LCD backlights).
3131.2005.12.1.2
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