AAT2845AIML-EE-T1 AnalogicTech, AAT2845AIML-EE-T1 Datasheet - Page 10

• Manufacturer Part Number: AAT2845AIML-EE-T1
• Description: Four-Channel Backlight Driver with Dual LDOs
• Manufacturer: AnalogicTech

Functional Block Diagram
Functional Description
The AAT2845A is an integrated solution for LCD
display applications with a built-in driver for white
LED backlight and two LDO voltage regulators for
logic power supplies.
The backlight driver is a tri-mode load switch (1X)
and high-efficiency (1.5X or 2X) charge pump
device. To maximize power conversion efficiency,
an internal sensing circuit monitors the voltage
required on each constant current sink input and
sets the load switch and charge pump modes
based on the input battery voltage and the current
sink input voltage. As the battery discharges over
time, the charge pump is enabled when any of the
four current sink inputs nears dropout. The charge
pump initially starts in 1.5X mode. If the charge
pump output droops enough for any current source
output to become close to dropout, the charge
pump will automatically transition to 2X mode. The
charge pump requires only four external compo-
nents: two 1µF ceramic capacitors for the charge
pump flying capacitors (C
10
EN/SET
ENLDO
CBP
IN
IN
1
and C
Reference
Interface
S
1.2V
2
Cwire
2
), one 1µF
GND
Reference
Oscillator
Soft-Start
Four-Channel Backlight Driver with Dual LDOs
Voltage
Control
1MHz
C1+
Bit ROM
LDO A
LDO B
6x16
(1X, 1.5X and 2X)
Charge Pump
C1- C2+
Tri-Mode
ceramic input capacitor (C
1µF ceramic charge pump output capacitor (C
The four constant current sink inputs (D1 to D4)
can drive four individual LEDs with a maximum cur-
rent of 20mA each. The unused sink inputs must be
connected to the OUT pin; otherwise the part will
operate only in 2X charge pump mode. The
S
and sets the current sink magnitudes.
Constant Current Output Level Settings
The constant current sink levels for D1 to D4 are
set via the S
logarithmic scale for the first 12 codes, and a sep-
arate low-current scale for the last four codes.
Because the inputs D1 to D4 are true independent
constant current sinks, the voltage observed on
any single given input will be determined by the dif-
ference between V
age (V
Since the current level is programmable, no PWM
(pulse width modulation) or additional control cir-
2
Cwire serial interface enables the charge pump
C2-
F
) of the LED being driven.
D/A
D/A
D/A
D/A
2
Cwire serial interface according to a
OUT
and the actual forward volt-
LDOA
LDOB
OUT
D1
D2
D3
D4
FBA
FBB
IN
), and one 0.33µF to
AAT2845A
2845A.2007.05.1.0
OUT
).