AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Pin Descriptions
Pin #
1
2
3
4, 5, 23, 24
6
7
8
9, 18
10
11
12
13
14, 21, 22
Symbol
BL3
BL2
BL1
AGND
REF
FBB
OUTB
IN
FBA
OUTA
C1-
C1+
OUT
Description
Backlight LED 3 current sink. BL3 controls the current through backlight LED 3. Connect
the cathode of backlight LED 3 to BL3. If not used, connect BL3 to OUT.
Backlight LED 2 current sink. BL2 controls the current through backlight LED 2. Connect
the cathode of backlight LED 2 to BL2. If not used, connect BL2 to OUT.
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.
Analog ground. Connect AGND to PGND at a single point as close to the AAT2856 as
possible.
Reference output. Bypass REF to AGND with a 0.1µF or larger ceramic capacitor.
Feedback input for LDO B. FBB measures the output voltage of LDO B. Connect a resistive
voltage divider from the output of LDO B to FBB. FBB feedback regulation voltage is 1.2V.
LDO B regulated voltage output. OUTB is the voltage output of LDO B. Bypass OUTB to
AGND with a 2.2µF or larger ceramic capacitor as close to the AAT2856 as possible.
Power input. Connect IN to the input source voltage. Bypass IN to PGND with a 4.7µF or
larger ceramic capacitor as close to the AAT2856 as possible.
Feedback input for LDO A. FBA measures the output voltage of LDO A. Connect a resistive
voltage divider from the output of LDO A to FBA. FBA feedback regulation voltage is 1.2V.
LDO A regulated voltage output. OUTA is the voltage output of LDO A. Bypass OUTA to
AGND with a 2.2µF or larger ceramic capacitor as close to the AAT2856 as possible.
Negative node of charge pump capacitor 1. Connect the 1µF charge pump capacitor 1
from C1+ to C1-.
Positive node of charge pump capacitor 1. Connect the 1µF charge pump capacitor 1 from
C1+ to C1-.
Charge pump output; supplies current to the backlight LEDs. Connect the backlight LED
anodes to OUT. Bypass OUT to PGND with a 2.2µF or larger ceramic capacitor as close
to the AAT2856 as possible.
LDO B enable input. ENB turns on or off low dropout regulator B (LDO B). Drive ENB high
to turn on LDO B; drive it low to turn it off.
Positive node of charge pump capacitor 2. Connect the 1µF charge pump capacitor 2 from
C2+ to C2-.
Negative node of charge pump capacitor 2. Connect the 1µF charge pump capacitor 2
from C2+ to C2-.
Power ground. Connect AGND to PGND at a single point as close to the AAT2856 as pos-
sible.
Backlight enable and serial control input. ENS turns the backlight on/off and is the
AS
2
Cwire input to serially control the backlightLED brightness.
Backlight LED 6 current sink. BL6 controls the current through backlight LED 6. Connect
the cathode of backlight LED 6 to BL6. If not used, connect BL6 to OUT.
Backlight LED 5 current sink. BL5 controls the current through backlight LED 5. Connect
the cathode of backlight LED 5 to BL5. If not used, connect BL5 to OUT.
LDO A enable input. ENA turns on or off low dropout regulator A (LDO A). Drive ENA high
to turn on LDO A; drive low to turn it off.
Backlight LED 4 current sink. BL4 controls the current through backlight LED 4. Connect
the cathode of backlight LED 4 to BL4. If not used, connect BL4 to OUT.
Exposed paddle (bottom); connect to ground as closely as possible to the device.
15
16
17
19
20
25
26
27
28
EP
ENB
C2+
C2-
PGND
ENS
BL6
BL5
ENA
BL4
2
2856.2007.06.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
