High-Current Charge Pump with S
2
Cwire™
Control and Dual LDO for Backlight and Flash
Pin Descriptions
Pin #
1
2
3
4
5
6
7
8
9, 18
10
11
12
13
14
AAT2842
Symbol
BL1
BSET
FSET
AGND
CT
REF
FBB
OUTB
IN
FBA
OUTA
C1-
C1+
OUT
Description
Backlight LED 1 current sink. BL1 controls the current through Backlight LED 1. Connect the
cathode of Backlight LED 1 to BL1. If not used, connect BL1 to OUT.
Backlight current setting input. A 280kΩ resistor from BSET to AGND sets the maximum back-
light current to 30mA.
Flash current setting input. A 280kΩ resistor from FSET to AGND sets the maximum flash cur-
rent to 150mA.
Analog ground. Connect AGND to PGND at a single point as close to the AAT2842 as possible.
Flash timer control capacitor input. Connect a capacitor from CT to AGND to set the flash timer.
A 100nF capacitor sets the timer to 1s.
Reference output. For low noise operation, bypass REF to AGND with capacitor. Typically, a
0.1µF ceramic capacitor provides sufficient noise reduction.
Feedback input for LDOB. FBB measures the output voltage of LDOB. Connect a resistive
voltage divider from the output of LDOB to FBB. FBB feedback regulation voltage is 1.2V.
LDOB regulated voltage output. OUTB is the voltage output of low dropout regulator B. Bypass
OUTB to AGND with a 2.2µF or larger ceramic capacitor as close to the AAT2842 as possible.
Power input. Connect IN to the input source voltage. Bypass IN to PGND with a 4.7µF or larg-
er ceramic capacitor as close to the AAT2842 as possible.
Feedback input for LDOA. FBA measures the output voltage of LDOA. Connect a resistive
voltage divider from the output of LDOA to FBA. FBA feedback regulation voltage is 1.2V.
LDOA regulated voltage output. OUTA is the voltage output of low dropout regulator A. Bypass
OUTA to AGND with a 2.2µF or larger ceramic capacitor as close to the AAT2842 as possible.
Negative node of charge pump capacitor 1.
Positive node of charge pump capacitor 1. Connect a 1µF ceramic capacitor from C1+ to C1-.
Charge pump output. OUT is the output of the charge pump and supplies current to the back-
light and flash LEDs. Connect the backlight and flash LED anodes to OUT. Bypass OUT to
PGND with a 2.2µF or larger capacitor as close to the AAT2842 as possible.
LDO enable input. ENL turns on or off the low dropout regulators. Drive ENL high to turn on
the regulators, drive it low to turn them off.
Positive node of charge pump capacitor 2. Connect a 1µF ceramic capacitor from C2+ to C2-.
Negative node of charge pump capacitor 2.
Power ground. Connect AGND to PGND at a single point as close to the AAT2842 as possible.
Flash LED 4 current sink. FL4 controls the current through Flash LED 4. Connect the cathode
of Flash LED 4 to FL4. If not used, connect FL4 to OUT.
Flash LED 3 current sink. FL3 controls the current through Flash LED 3. Connect the cathode
of Flash LED 3 to FL3. If not used, connect FL3 to OUT.
Flash LED 2 current sink. FL2 controls the current through Flash LED 2. Connect the cathode
of Flash LED 2 to FL2. If not used, connect FL2 to OUT.
Flash LED 1 current sink. FL1 controls the current through Flash LED 1. Connect the cathode
of Flash LED 1 to FL1. If not used, connect FL1 to OUT.
15
16
17
19
20
21
22
23
ENL
C2+
C2-
PGND
FL4
FL3
FL2
FL1
2
2842.2006.10.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
