AAT3119 Datasheet, PDF (13/18 Pages) Advanced Analogic Technologies – High Efficiency 2X Charge Pump

AAT3119
High Efficiency 2X Charge Pump
C_FLY
1μF
V
BATTERY
C1+ C1-
IN
C_IN
1μF
OUT
AAT3119
Enable
EN
GND
C_OUT
1μF ^{D1 D2 D3 D4 D5 D6}
R_B1
R_B2
R_B3
R_B4
R_B5
R_B6
Figure 1: White LED Driver.
Flash LED Driver
The AAT3119 can source 250mA for pulsed loads
up to 500ms from an input supply as low as 3.3V.
This makes the device well suited for low-cost flash
LED driver applications in portable products.
Typically the 4.5V output version of the AAT3119
should be selected for photo-flash LED applica-
tions, as it can maintain better voltage regulation at
higher pulsed load current levels (refer to Figure 2).
The limitation of this option is that the greatest flash
LED forward voltage (V_F) that can be driven is 4.5V
at the maximum set forward current (I_F) for the
application. Flash LEDs with forward voltage (V_F)
levels up to 5.0V can be driven by the AAT3119
5.0V output option. However, the maximum cur-
rent for a 500ms pulse will be reduced. Refer to
the Typical Characteristics curves for peak output
current levels for a given minimum input voltage.
The forward current (I_F) through the flash LED may
be determined with the use of a series ballast resis-
tor. The typical forward voltage (V_F) for the flash
LED in a given application should be derived from
the LED manufacturer's datasheet for the desired
forward current (I_F) of the flash application. Once
the forward current has been determined, the flash
ballast resistor can be calculated using the follow-
ing equation:
R_F =
(V_OUT - V_F)
I_F
Where:
R_F =
V_OUT =
Flash ballast resistor value in ohms (Ω)
Regulated charge pump output voltage
(typically 4.5V)
V_F = Flash LED forward voltage at the
desired forward current
I_F = Desired flash LED forward current
The flash LED function can be controlled by the
AAT3119 enable pin in most applications. The
device start-up time into a maximum load is about
200μs, thus eliminating the need for pre-flash con-
trol synchronization.
3119.2007.02.1.2
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