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AAT2824 Schematic ( PDF Datasheet ) - Advanced Analogic Technologies

Teilenummer AAT2824
Beschreibung (AAT2822 - AAT2825) TFT-LCD DC-DC Converter
Hersteller Advanced Analogic Technologies
Logo Advanced Analogic Technologies Logo 




Gesamt 28 Seiten
AAT2824 Datasheet, Funktion
SystemPowerTM
PRODUCT DATASHEET
AAT2822/23/24/25www.DataSheet4U.com
TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer
General Description
The AAT2822-AAT2825 family of integrated panel power
solutions provides the regulated voltages required by an
active-matrix thin-film transistor (TFT) liquid-crystal dis-
play (LCD). The AAT2822 includes a triple-output DC-DC
converter, a LED backlight driver, and a VCOM buffer in
a 4 mm x 4mm TQFN package. The primary 1.3MHz
DC-DC boost converter uses an ultra-small inductor and
ceramic capacitor to generate output voltage (VAVDD) of
up to 14.5V for the charge pumps. The low on-resistance
of the integrated power MOSFET allows for efficiency up
to 93%.
The two charge pumps independently regulate a positive
output (VGH) and a negative output (VGL). These low-
power outputs use external diode and capacitor stages
to regulate output voltages up to +30V and down to
-30V. A proprietary regulation algorithm minimizes out-
put ripple when using small capacitors.
The high efficiency backlight driver provides a constant
current output capable of boosting up to 28V. The driver
is an ideal power solution for backlight applications with
up to seven white LEDs in series or up to 39 white LEDs
in a parallel and series configuration. LED brightness is
PWM controlled up to 1kHz. Filtered PWM is supported
for higher frequencies.
The high slew rate operational amplifier is suitable for
VCOM buffering and gain adjustment.
The sequencing of the power supplies ensures proper
panel startup and avoid damage to the device.
The AAT2822 family is available in a Pb-free, 24-pin 4 x
4mm TQFN package and operates over the -40°C to
+85°C temperature range.
Features
LCD Bias Power
• 2.5V to 5.5V Input Supply Range
• 1.3MHz Fixed Frequency Current-Mode Step-Up
Regulator
• Fast Transient Response
• Adjustable Voltage up to 14.5V
±1% Typical Accuracy
• High Efficiency (93%) @ 50mA Output Current
• Small External Inductor and Capacitors
• Integrated Soft Start and Sequencing of All Rails
• Short-Circuit, Over-Voltage, and Over-Temperature
Protection
Positive Output, VGH
Up to 13.2V Input Supply (VDD)
• Adjustable Voltage up to 30V @ 20mA
±3% Typical Accuracy
Negative Output, VGL
Up to 13.2V Input Supply (VDD)
• Adjustable Voltage down to -30V @ 20mA
± 3% Typical Accuracy
WLED Driver
• Input Voltage Range: 2.5V to 25V
• Maximum Continuous Output:
12V @ 260mA
28V @ 50mA
• Panel sizes from 5" – 10"
5.0" 3S5P
5.6" 3S6P
7.0" 3S9P
8.0" 3S10P/11P
10" 3S13P
• Constant LED Current with 6% Accuracy
• PWM Dimming Control
Up to 1kHz
• 1.3MHz Switching Fixed Frequency
Up to 90% Efficiency
VCOM Buffer
• High-Performance
13V/μs Slew Rate
12MHz, -3dB Bandwidth
• ±75mA Output Short-Circuit Current
• Low 1.5mA Quiescent Current
Applications
• Automotive Displays
• Digital Photo Frames
• Netbooks
• PNDs
2822.2010.02.1.0
www.analogictech.com
1






AAT2824 Datasheet, Funktion
SystemPowerTM
PRODUCT DATASHEET
AAT2822/23/24/25www.DataSheet4U.com
TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer
Electrical Characteristics
VIN = 5V, EN = WEN = WDIM = VIN, VAVDD = VDD = 12V, TA = -40°C to 85°C unless otherwise noted. Typical values are
at TA = 25°C.
Symbol Description
Power Supply
VIN
VUVLO
UVLOHYS
IIN
Input Voltage Range
Under-Voltage Lockout Threshold
UVLO Hysteresis
IN Quiescent Current
ISHDN
Shutdown Current
REF Output Voltage
VREF REF Load Regulation
REF Current
TSD Thermal Shutdown
Main Step-Up Regulator
Conditions
Rising Edge
VFB = VFBP = 0.7V, VFBN = -0.1, LX not switching
EN = WEN = Low, ISHDN = IIN + IDD, VDD = 5V
No load
0 < ILOAD < 50μA
In regulation
Temperature rising
Hysteresis
VAVDD
Output Voltage Range
FOSC
DCMAX
Operating Frequency
Maximum Duty Cycle
VFB FB Regulation Voltage
FB Fault Trip Level
FB Load Regulation
FB Line Regulation
FB Input Bias Current
RLX(ON) LX On-Resistance
ILX LX Leakage Current
ILIM LX Current Limit
tSS Soft-Start Period
Gate High Charge Pump (VGH)
VDD VDD Input Supply Range
Operating Frequency
VFBP FBP Regulation Voltage
FBP Fault Trip Level
IFBP FBP Input Bias Current
DRVPPRDS DRVP PCH ON-Resistance
DRVPNRDS DRVP NCH On-Resistance
Gate Low Charge Pump (VGL)
VDD VDD Input Supply Range
Operating Frequency
VFBN
FBN Regulation Voltage
FBN Fault Trip Level
IFBN FBN Input Bias Current
DRVNPRDS DRVN PCH ON-Resistance
DRVNNRDS DRVN NCH On-Resistance
No Load
VFB falling
0 < IAVDD < full load
VIN = 2.5V to 5.5V
VFB = 0.7V
ILX = 200mA
VLX = 13.2V
VFB = 0.7V, duty cycle = 75%
VFBP Falling
VFBP = 0.7V
VFBP = 0.585V
VFBP = 0.615V
VFBN Rising
VFBN = -0.1V
VFBN = 0.035V
VFBN = -0.025V
Min Typ Max
2.5
1.182
50
2.4
50
1.1
1.20
+140
15
5.5
2.5
1.6
1
1.218
10
VIN -
VDIODE
910
86
0.588
0.535
-1
1
1300
90
0.6
0.546
0.01
0.1
350
0.01
1.3
14.5
1690
0.612
0.557
±0.4
+1
700
20
2.7 13.2
0.588
FOSC
0.6
0.612
470 530
-1 +1
36
1.5 3
20
2.7 13.2
FOSC
-50 0 +50
408 425 442
-1 +1
36
1.5 3
20
Units
V
V
mV
mA
μA
V
mV
μA
OC
V
kHz
%
V
V
%/mA
%/V
μA
mΩ
μA
A
ms
V
kHz
V
mV
μA
Ω
Ω
kΩ
V
Hz
mV
mV
μA
Ω
Ω
kΩ
6
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2822.2010.02.1.0

6 Page









AAT2824 pdf, datenblatt
SystemPowerTM
PRODUCT DATASHEET
AAT2822/23/24/25www.DataSheet4U.com
TFT-LCD DC-DC Converter with WLED Driver and VCOM Buffer
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.
If the OVP input voltage is exceeded the WLED driver
continues to regulate at the OVP threshold.
Start
EN High
Yes
WLED Boost
No
VCOM Buffer: Operational Amplifier
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)
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.
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.
VWLED>VOVP
Yes
No
Stop Switching
Figure 1: WLED Driver Operation.
12
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2822.2010.02.1.0

12 Page





SeitenGesamt 28 Seiten
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