AAT2801IXN-4.5-T1 AnalogicTech, AAT2801IXN-4.5-T1 Datasheet - Page 18

• Manufacturer Part Number: AAT2801IXN-4.5-T1
• Description: Multi-Mode Charge Pump for White LED Backlight and Flash Applications
• Manufacturer: AnalogicTech

The forward current (I
be determined with the use of a series ballast resis-
tor. The typical forward voltage (V
LED in a given application should be derived from
the LED manufacturer's datasheet for the desired
forward current (I
the forward current has been determined, the flash
ballast resistor can be calculated using the follow-
ing equation:
Where:
R
V
V
I
The flash LED function can be controlled by the
AAT2801 flash enable (EN_FLSH) pin in most
18
F
OUT
F
B
=
=
=
=
Flash Enable
Flash ballast resistor value in ohms (Ω)
Regulated charge pump output voltage
(typically 4.5V)
Flash LED forward voltage at the
desired forward current
Desired flash LED forward current
R
F
) of the flash application. Once
V
B
IN
=
F
) through the flash LED may
(V
OUT
I
1μF
C
F
- V
IN
F
)
F
) for the flash
EN_FLSH
IN
Figure 1: Flash LED Application.
AAT2801
C3+
OUT_FLSH
White LED Backlight and Flash Applications
1μF
C
3
C3-
4.5V
applications. The device start-up time into a maxi-
mum load is about 200µs, thus eliminating the
need for pre-flash control synchronization.
If a "light" or "movie" mode is also needed along
with the flash function, this can be accomplished
with the addition of a second ballast resistor with a
flash function gating MOSFET switch as shown in
Figure 2. Refer to the following equations for the
calculation of flash and light resistors, R
Where:
R
V
V
I
F
OUT
F
L
1μF
C
F
=
=
=
=
Multi-Mode Charge Pump for
Light mode ballast resistor value in
ohms (Ω)
Regulated charge pump output voltage
(typically 4.5V)
Flash LED forward voltage at the
desired forward current
Desired flash LED forward current in
the "light" mode
R
B
R
L
=
(V
OUT
I
F
- V
Flash LED
F
)
2801.2006.04.1.3
B
and R
L
.