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| AAT3122_05 Datasheet, PDF (11/12 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications | |||
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AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
Additional Application Circuit
VBATTERY
VIN
C1+
C1
1µF
VOUT
C1-
C2+
CIN
1µF
COUT
1µF
AAT3122
C2
1µF
C2-
D1
D2
D3
D4
D5
D6
D1
RB*
RB*
RB*
RB*
RB*
RB*
EN/SET
EN/SET
GND
*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 approxiamted by the following equation:
RB
=
(VIN(MIN))1.5 - (VF(MAX)
IF(MAX)
+
250mV)
VF(MAX) = Maximum expected LED forward voltage at the given maximum forward current level. Refer to the LED manufacturersâ
datasheet for maximum VF specifications.
IF(MAX) = Maximum forward current used to drive an individual LED.
VIN(MIN) = Minimum input supply voltage for the application.
RB = Ballast resistor value in ohms.
3122.2005.11.1.3
11
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