AAT2869 Advanced Analogic Technologies, Inc., AAT2869 Datasheet - Page 11

• Manufacturer Part Number: AAT2869
• Description: Fade-in/fade-out 4 Channel Backlight Driver With Dual Ldos
• Manufacturer: Advanced Analogic Technologies, Inc.

Functional Block Diagram
Functional Description
The AAT2869 is a high efficiency charge pump white LED
driver for portable applications. It can drive up to 4 white
LEDs. The two integrated LDOs can provide 1.2V, 1.5V,
1.8V, 2.8V and 3.0V output voltages in 16 combinations
with up to 150mA load capability.
The AAT2869's charge pump is a fractional charge pump
and can multiply the input voltage by 1 or 1.5 times. The
charge pump switches at a fixed frequency of 0.9MHz.
The internal mode-selection circuit automatically switch-
es the mode between 1x and 1.5x based on the input
voltage, white LED forward voltage V
grammed LED current. This mode switching maximizes
the efficiency throughout the entire LED load range.
When the input voltage is high enough, the charge pump
operates in 1x mode (no charge pump) to provide max-
imum efficiency. If the input voltage is too low to supply
the programmed LED current, typically when the battery
discharges and the voltage decays, the 1.5x charge
pump mode is automatically enabled. When the battery
is connected to a charger and the input voltage rises suf-
ficiently, the device will switch back to 1x mode.
2869.2010.01.1.0
SystemPower
TM
EN/SET
INLDO
FCAP
C1+
C2+
C1-
C2-
IN
Fade-In/Fade-Out 4 Channel Backlight Driver with Dual LDOs
F
, and the pro-
32-step AS
Backlight Control
and LDO Setting
Charge Pump
Dual-mode
Fade Filter
1X/1.5X
w w w . a n a l o g i c t e c h . c o m
2
Cwire
GND
4
AGND
Six registers are designed for charge pump enable/dis-
able control, LED current programming, fade-in, fade-
out enable/disable, two LDOs enable/disable control and
LDO output voltage combination setting through the
AS
rent value is programmed by the EN/SET serial data
AS
edges of the EN/SET pin and decodes them into 32 indi-
vidual current level settings from 0.4mA to 31mA. To get
a visual fade in and fade out effect, a small external
capacitor is used to set LED current rising exponentially
to the programmed value and decreasing exponentially
to the programmed floor LED current level.
The AAT2869 has five registers with up to four bits each
to control LED backlighting enable/disable, LED current,
enable/disable for the two LDOs, output voltages, etc. as
shown in Table 1. Each data register can be written with
1 to 16 EN/SET rising edges. Some bits are internally
reserved and should only be written with data 0, such as
address 0, bit D0, D1 and D3, etc. in order to avoid
unexpected results. Address 0 is the default address.If
EN/SET is pulled high after a low level lasting for at least
2
2
Cwire interface. After writing address 3, the LED cur-
Cwire interface. The AS
Control
Logic
PRODUCT DATASHEET
2
Cwire interface records rising
OUTCP
LDOA
LDOB
D1
D2
D3
D4
AAT2869
11