DATA SHEET
AAT2822/2823/2824/2825
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
inductor, output capacitor, and sense resistors are
VCOM Buffer: Operational Amplifier
required to implement a DC/DC constant current boost
converter. Integrated soft-start circuitry minimizes the
start-up inrush current and eliminates output voltage
overshoot across the full input voltage range and all load
conditions. The backlight current is set by an external
ballast resistor up to a maximum of 260mA at 12V or
50mA at 28V output. Brightness control is via PWM dim-
ming at up to 1kHz. Higher frequencies are achieved by
filtered PWM. The AAT2822 can drive from 3 LEDs in
series up to a maximum of 7 LEDs, making it suitable for
screen sizes from 5” up to 10”. Depending upon the
number of LEDs required, up to 9 parallel strings can be
successfully driven.
The operational amplifier drives the LCD backplane
VCOM. The operational amplifier features +/- 75mA(min)
output short-circuit current, 13V/μs slew rate, and
12MHz bandwidth. Internal short-circuit protection limits
the short circuit current while the output is directly
shorted.
Power Supply Sequencing
The AAT2822 family has integrated power supply sequenc-
ing to prevent damage to the LCD screen. Two sequences
are available to swap the startup of the positive and
negative gate drive voltages. The startup sequence for
the “-1” option establishes main boost supply (VAVDD
)
If the OVP input voltage is exceeded the WLED driver
continues to regulate at the OVP threshold.
first, followed by the gate voltages VGL then VGH. The
sequence for the plain option is to establish VAVDD first
followed by VGH then VGL. The WLED backlight driver is
independently controlled by WEN and WDIM.
Start
Operating Faults
The AAT2822 family continuously monitors for fault con-
ditions on the main boost converter and charge pumps
according to defined fault trip levels. During operation if
any fault conditions persist the controller will shut down
all supplies. After removing the fault conditions, recycle
the enables to start up the supplies.
EN High
No
Yes
WLED Boost
VWLED > VOVP
No
Yes
Stop Switching
Figure 1: WLED Driver Operation.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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202081B
• Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
