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參數(shù)資料
| 型號： | TQFN34-20 |
| 廠商： | ANADIGICS, Inc. |
| 英文描述： | Four-Channel Backlight Driver with Dual LDOs |
| 中文描述： | 四通道雙LDO的背光驅(qū)動器 |
| 文件頁數(shù)： | 11/20頁 |
| 文件大小： | 392K |
| 代理商： | TQFN34-20 |
AAT2847
Four-Channel Backlight Driver with Dual LDOs
2847.2007.09.1.0
11
Functional Block Diagram
Tri-Mode
(1x, 1.5x and 2x)
Charge Pump
D/A
D/A
D/A
D/A
6 x16 bit
ROM
AS
2
Cwire
Interface
1MHz
Oscillator
Voltage
Reference
IN
EN/SET
GND
D4
D3
D2
D1
OUT
C1+
C1- C2+
C2-
LDO A
IN
LDOA (2.8V/2.8V)
FBA (NC)
LDO B
LDOB (1.5V/1.8V)
FBB (NC)
ENA
1.2V
Reference
AAT2847-EE
(AAT 2847-QG/-QI)
(AAT 2847-QG/-QI)
PGND
ENB
Functional Description
The AAT2847 is an integrated solution for LCD dis-
play applications with a built-in four channel white
LED driver (charge pump) and dual 200mA LDO
voltage regulators. The AAT2847 incorporates a
tri-mode charge pump with load switch (1X) func-
tionality and high efficiency (1.5X or 2X) perform-
ance. To maximize power conversion efficiency, an
internal sensing circuit monitors the voltage
required at each white LED cathode input pin (D1-
D4) and sets the load switch and charge pump
mode based on the input battery voltage and the
white LED cathode pin voltage. The voltage thresh-
old for 1X to 1.5X and 1.5X to 2X mode transitions
is V
TH
.
The charge pump in the AAT2847 starts-up in 1X
mode (default); under this condition, if the LED
cathode input pin voltage is below V
TH
the
AAT2847 will transition into 1.5X mode. When
1.5X mode does not provide enough current
through the white LEDs for backlight applications,
which occurs during the normal discharge of the
input battery power source, the LED cathode input
pin voltage will drop below V
TH
and the AAT2847
will transition into 2X mode. The charge pump
requires only four external capacitors, 1μF ceramic
capacitors for the flying (C1 and C2), input (C
IN
),
and output (C
OUT
) capacitors.
The four LED cathode input pins (D1-D4) can drive
individual LEDs with a maximum current of 30mA
each. The unused LED cathode input pins have to
be connected to the OUT pin, otherwise the
AAT2847 will operate in 2X mode only. Operating
in 2X mode when it is not necessary will result in a
significant reduction in efficiency. The AS
2
Cwire
serial interface enables the charge pump and sets
the current flowing into the LED cathode input pins.
The AAT2847 also contains dual LDO voltage reg-
ulators that have separate enable pins from each
other and the charge pump. The separate enable
pins for each DC/DC device in the AAT2847 allow
for every possible device operational combination.
The two LDO regulators require 2.2μF output
capacitors for stable operation.
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