AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
1
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
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
• 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
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
2Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Typical Application
VIN
LX
FB
COMP
DRVP
FBP
FBN
DRVN
REF
V
GL
V
AVDD
RIN RFB1
RFB2
CIN2
CAVDDOUT
CDRVP
CDRVN
D1
R
COMP
RFBP1
C
IN1
CVGH
C
COMP
CWIN
CVGL
C
REF
D2
D3
VDD
V
IN
V
GH
V
LED
WLX
OVP
WEN
WDIM
WFB
PWM
ON
OFF
EN
ON
OFF
L2
D2
R
BAL
Up to 13 strings
OPIN
OP -
OUT
OP+
AGND PGND1
PGND2
WCOMP
R
WCOMP
C
WCOMP
VAVDD
VCOM_IN
VCOM_OUT
ROP1
ROP2
CWOUT
CCOMOUT
V
IN
V
DD
L1
2.5V - 5.5V
2.5V - 5.5V
RFBN1
RFBP2
RFBN2
ROVP1
ROVP2
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
3
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
1. Future products. Please contact factory for availability.
Pin Descriptions
Pinout is preliminary and subject to change during development.
Pin Number
Symbol Function DescriptionAAT2822 AAT2823 AAT28241AAT28251
1 1 n/a n/a WLX OBoost inductor node. Connect an inductor between IN and WLX.
WLX is high impedance in shutdown.
2 2 2 2 PGND2 I/O Power ground. Connect to GND underneath the IC.
3 3 3 3 REF O
Internal reference bypass terminal. Connect a 0.1µF capaci-
tor from this terminal to analog ground (GND). External load
capability to 50µA.
4 4 4 4 FBN INegative charge-pump regulator feedback input. Regulates to
0V nominal.
5 5 n/a n/a WEN IActive high logic level enable for WLED Driver.
6 6 6 6 DRVN ONegative charge-pump driver output. Output high level is VDD,
and low level is PGND.
7 7 7 7 VDD PI Positive and negative charge-pump driver supply voltage. By-
pass to PGND with a 0.1µF capacitor.
8 8 8 8 DRVP OPositive charge-pump driver output. Output high level is VINP,
and low level is PGND.
9 9 9 9 EN IActive high logic level enable input. Connect EN to IN for normal
operation.
10 10 10 10 FBP I
Positive charge-pump regulator feedback input. Regulates to
0.6V nominal. Connect feedback resistive divider to analog
ground (GND).
11 11 11 11 PGND1 I/O Power ground. Connect to GND underneath the IC.
12 12 12 12 LX OMain boost regulator power MOSFET N-channel drain. Connect
output diode and output capacitor as close to PGND as possible.
13 13 13 13 COMP IStep-up regulator error-amplier compensation point. Connect
a series RC from COMP to AGND.
14 14 14 14 FB O
Main boost regulator feedback input. Regulates to 0.6V nomi-
nal. Connect feedback resistive divider to analog ground (GND)
to set output voltage.
15 n/a 15 n/a OPIN I
Operational-amplier power input. Power supply rail for the
operational ampliers. Typically connected to VAVDD. Bypass
OPIN to GND with a 0.1µF capacitor.
16 n/a 16 n/a OP+ IOperational-amplier non-inverting input.
17 n/a 17 n/a OP- IOperational-amplier inverting input.
18 n/a 18 n/a OUT OOperational-amplier output.
19 19 n/a n/a WCOMP IWhite LED driver error-amplier compensation point. Connect a
series RC from WCOMP to AGND.
20 20 n/a n/a WFB OFeedback pin. Connect a resistor to ground to set the maximum
LED current.
21 21 n/a n/a OVP OFeedback pin for over-voltage protection sense. Connect a re-
sistive divider between the boost converter output and ground.
22 22 22 22 VIN ISupply input. +2.5V to +5.5V input range. Bypass with a 0.1µF
capacitor between IN and GND, as close to the pins as possible.
23 23 AGND AGND AGND I/O Analog ground. Connect to power ground (PGND) underneath
the IC.
24 24 n/a n/a WDIM I
Dimming control input. Apply a PWM signal up to 1kHz to adjust
the WLED brightness from 100% to 5%, proportional to the
duty cycle of the PWM signal.
n/a 15, 16,
17, 18
1, 19, 20,
21
1, 15, 16, 17,
18, 19, 20, 21 N/C Not connected.
EP EP 5, 24, EP 5, 24, EP GND Ground. EP = Exposed paddle, connect to PCB ground plane.
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
4Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Pin Configurations
TQFN44-24
(Top View)
AAT2822 AAT2823
1
3
2
5
4
6
18
16
17
14
15
13
10
11
12
8
9
7
19
21
20
23
22
24
WLX
PGND2
REF
FBN
WEN
DRVN
VDD
DRVP
EN
FBP
PGND1
LX
OPIN
OP+
FB
COMP
OP-
OUT
EP
WCOMP
WFB
OVP
VIN
AGND
WDIM
1
3
2
5
4
6
18
16
17
14
15
13
10
11
12
8
9
7
19
21
20
23
22
24
WLX
PGND2
REF
FBN
WEN
DRVN
VDD
DRVP
EN
FBP
PGND1
LX
N/C
N/C
FB
COMP
N/C
N/C
EP
WCOMP
WFB
OVP
VIN
AGND
WDIM
AAT2824 AAT2825
1
3
2
5
4
6
18
16
17
14
15
13
10
11
12
8
9
7
19
21
20
23
22
24
N/C
PGND2
REF
FBN
GND
DRVN
VDD
DRVP
EN
FBP
PGND1
LX
OPIN
OP+
FB
COMP
OP-
OUT
EP
N/C
N/C
N/C
VIN
AGND
GND
1
3
2
5
4
6
18
16
17
14
15
13
10
11
12
8
9
7
19
21
20
23
22
24
N/C
PGND2
REF
FBN
GND
DRVN
VDD
DRVP
EN
FBP
PGND1
LX
N/C
N/C
FB
COMP
N/C
N/C
EP
N/C
N/C
N/C
VIN
AGND
GND
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
5
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board.
3. Derate 20mW/°C above 25°C.
Part Number Descriptions
Part Number LCD Bias Startup Sequence Backlight VCOM Buffer
AAT2822 VAVDD->VGH->VGL
AAT2822-1 VAVDD->VGL->VGH
AAT2823 VAVDD->VGH->VGL
AAT2823-1 VAVDD->VGL->VGH
AAT2824 VAVDD->VGH->VGL
AAT2824-1 VAVDD->VGL->VGH
AAT2825 VAVDD->VGH->VGL
AAT2825-1 VAVDD->VGL->VGH
Absolute Maximum Ratings1
Description Value Units
VIN, EN -0.3 to 7
V
VDD, OPIN, OUT, OP+, OP- -0.3 to 15
LX, WLX -0.3 to 30
WCOMP, COMP, FB, FBP, FBN, REF, WEN, PWM, WFB, OVP -0.3 to VIN + 0.3
DRVP -0.3 to (VDD + 0.3)
DRVN -0.3 to (VDD + 0.3)
Thermal Information2
Symbol Description Value Units
ΘJA Thermal Resistance350 °C/W
PDMaximum Power Dissipation 2 W
TJOperating Junction Temperature Range -40 to 150 °C
TLEAD Maximum Soldering Temperature (at Leads) 300
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
6Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
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 Conditions Min Typ Max Units
Power Supply
VIN Input Voltage Range 2.5 5.5 V
VUVLO Under-Voltage Lockout Threshold Rising Edge 2.4 2.5 V
UVLOHYS UVLO Hysteresis 50 mV
IIN IN Quiescent Current VFB = VFBP = 0.7V, VFBN = -0.1, LX not switching 1.1 1.6 mA
ISHDN Shutdown Current EN = WEN = Low, ISHDN = IIN + IDD, VDD = 5V 1 µA
VREF
REF Output Voltage No load 1.182 1.20 1.218 V
REF Load Regulation 0 < ILOAD < 50µA 10 mV
REF Current In regulation 50 µA
TSD Thermal Shutdown Temperature rising +140 OC
Hysteresis 15
Main Step-Up Regulator
VAVDD Output Voltage Range VIN -
VDIODE
14.5 V
FOSC Operating Frequency 910 1300 1690 kHz
DCMAX Maximum Duty Cycle 86 90 %
VFB FB Regulation Voltage No Load 0.588 0.6 0.612 V
FB Fault Trip Level VFB falling 0.535 0.546 0.557 V
FB Load Regulation 0 < IAVDD < full load 0.01 %/mA
FB Line Regulation VIN = 2.5V to 5.5V 0.1 ±0.4 %/V
FB Input Bias Current VFB = 0.7V -1 +1 µA
RLX(ON) LX On-Resistance ILX = 200mA 350 700 mΩ
ILX LX Leakage Current VLX = 13.2V 0.01 20 µA
ILIM LX Current Limit VFB = 0.7V, duty cycle = 75% 1 A
tSS Soft-Start Period 1.3 ms
Gate High Charge Pump (VGH)
VDD VDD Input Supply Range 2.7 13.2 V
Operating Frequency FOSC kHz
VFBP FBP Regulation Voltage 0.588 0.6 0.612 V
FBP Fault Trip Level VFBP Falling 470 530 mV
IFBP FBP Input Bias Current VFBP = 0.7V -1 +1 μA
DRVPPRDS DRVP PCH ON-Resistance 3 6 Ω
DRVPNRDS DRVP NCH On-Resistance VFBP = 0.585V 1.5 3 Ω
VFBP = 0.615V 20 kΩ
Gate Low Charge Pump (VGL)
VDD VDD Input Supply Range 2.7 13.2 V
Operating Frequency FOSC Hz
VFBN FBN Regulation Voltage -50 0 +50 mV
FBN Fault Trip Level VFBN Rising 408 425 442 mV
IFBN FBN Input Bias Current VFBN = -0.1V -1 +1 μA
DRVNPRDS DRVN PCH ON-Resistance 3 6 Ω
DRVNNRDS DRVN NCH On-Resistance VFBN = 0.035V 1.5 3 Ω
VFBN = -0.025V 20 kΩ
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
7
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Electrical Characteristics
VIN = 5V, EN = WEN = WDIM = VIN, VAVDD = VDD = 12V, TA = -40oC to 85oC unless otherwise noted. Typical values are
at TA = 25oC.
Symbol Description Conditions Min Typ Max Units
WLED Driver (AAT2822, AAT2823 Only)
VLED Output Voltage VIN -
VDIODE
28 V
IOUT Maximum Continuous Output Current VLED = 28V 50 mA
≥VFB/
≥VIN
Line Regulation VIN = 2.5V to 5.5V 0.7 %/V
RDS(ON) Low Side Switch On-Resistance 300 mΩ
VWFB WFB Pin Regulation 0.282 0.3 0.318 V
TSS Soft-Start Time From Enable to Output Regulation;
VFB = 300mV 300 µs
VOVP Over-Voltage Protection Threshold VLED Rising 0.55 0.60 0.65 V
OVHYS Over-Voltage Hysteresis VLED Falling 25 mV
ILIMIT N-Channel Current Limit 1.3 A
FPWM Maximum WDIM PWM Frequency 1 kHz
DCMIN Minimum Duty Cycle 5 %
VCOM Buffer (AAT2822 , AAT2824 Only)
VOPIN Supply Range 4.5 13.2 V
IOPIN Supply Current 1.5 2.5 mA
VOS Input Offset Voltage (VNEG, VPOS, VOUT) ≡ VSUP/2 12 mV
VCM Input Common-Mode Range 0 VSUP V
VOH Output Voltage Swing, High IOUT = 5mA VSUP -
150 mV
VOL Output Voltage Swing, Low IOUT = -5mA 150 mV
ISC Short-Circuit Current VSUP/2 Source 75 mA
Sink 75
GBW Gain Bandwidth Product 12 MHz
SR Slew Rate 13 V/µs
Logic
WDIM/
WENL/ENL
Enable Input Low Voltage VIN = 2.5V 0.4 V
WDIM/
WENH/ENH
Enable Input High Voltage VIN = 5.5V 1.4 V
IEN WDIM/WEN/EN Input Current 1 µA
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
8Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Typical Characteristics
Oscillator Frequency vs. Temperature
Temperature (°C)
Oscillator Frequency (mHz)
-40-15 10 35 60 85
1.235
1.240
1.245
1.250
1.255
1.260
1.265
1.270
1.275
1.280
1.285
Power Up Sequencing
(VAVDD→VGH→VGL; VIN = 5.0V)
Time (500µs/div)
EN/SET
(5V/div)
VAVDD
(5V/div)
VGL
(20V/div)
VGH
(20V/div)
Power Up Sequencing
(VAVDD->VGL->VGH; VIN = 5.0V)
Time (1ms/div)
EN/SET
(2V/div)
VAVDD
(2V/div)
VGL
(10V/div)
VGH
(10V/div)
Main Boost Efficiency
(VOUT = 12V)
Output Current (mA)
Efficiency (%)
050 100 200150 300250 400350 500450
0
10
20
30
40
50
60
70
80
90
100
Main Boost Load Transient
(VIN = 5.0V)
Time (500µs/div)
VOUT
(100mV/div)
IOUT
(50mA/div)
100mA
10mA
Line Regulation
Input Voltage (V)
Output Voltage (V)
2.73.73.
24
.74.
25
.2
11.75
11.80
11.85
11.90
11.95
12.00
12.05
12.10
12.15
12.20
12.25
IOUT = 1mA
IOUT = 10mA
IOUT = 100mA
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
9
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Typical Characteristics
VGH vs. Temperature
Temperature (°C)
VGH (V)
-40-15 10 35 60 85
29.5
29.6
29.7
29.8
29.9
30.0
30.1
30.2
30.3
30.4
30.5
VGH Load Regulation
Load Current (mA)
Positive Output Voltage (V)
024861210 1614 2018
29.5
29.6
29.7
29.8
29.9
30.0
30.1
30.2
30.3
30.4
30.5
5.0V
2.7V
VGL vs. Temperature
Temperature (°C)
VGL (V)
-40-15 10 35 60 85
-30.50
-30.40
-30.30
-30.20
-30.10
-30.00
-29.90
-29.80
-29.70
-29.60
-29.50
VGL Load Regulation
Load Current (mA)
Negative Output Voltage (V)
024861210 1614 2018
-30.5
-30.4
-30.3
-30.2
-30.1
-30.0
-29.9
-29.8
-29.7
-29.6
-29.5
5.0V
2.7V
WLED Efficiency vs. Load Current
(7S3P; VIN = 5V; VL = 12V)
Load Current (mA)
Efficiency (%)
010204030 6050 8070 10090
0
10
20
30
40
50
60
70
80
90
WLED Operation at 300mA Load
(VIN = 5.0V, 3S13P)
Time (200µs/div)
VLED
(5V/div)
ILED
(500mA/div)
VOUT
(100mV/div)
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Typical Characteristics
VCOM Buffer Supply Current vs. Temperature
(VIN = 5.0V, VOPIN = 12V)
Temperature (°C)
VGL (V)
-40-15 10 35 60 85
1.50
1.55
1.60
1.65
1.70
1.75
1.80
1.85
1.90
1.95
2.00
VCOM Input Offset Voltage vs. Temperature
(VIN = 5.0V, VOPIN = 12V)
Temperature (°C)
Input Offset Voltage (mV)
-40-15 10 35 60 85
0.0
0.5
1.0
1.5
2.0
2.5
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
11
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Functional Block Diagram
AAT2822
Step-up
Controller
Charge
Pump
Control
Reference
OP
WLED
Control
VDD
FBN
REF
VIN
COMP
LX
FB
DRVP
FBP
DRVN
WFB
OPIN
OP-
OUT
OP+
Brightness
Control
OVP
WLX
WEN
WDIM
EN
WCOMP
AGND PGND1 PGND2
Functional Description
Main Boost Converter
The main boost regulator contains a current-mode,
fixed-frequency PWM architecture to maximize loop
bandwidth and provide fast transient response to pulsed
loads typical of TFT-LCD panel source drivers. The
1.3MHz switching frequency allows the use of low profile,
low value inductors and ceramic capacitors to minimize
the thickness of LCD panel designs.
Dual Charge-Pump Regulator
The AAT2822 provides low-power regulated output volt-
ages from two individual charge pumps to provide the
VGH and VGL supplies. Using a single stage, the VGL
charge pump inverts the supply voltage (VDD) and pro-
vides a regulated negative output voltage. The VGH
charge pump doubles VDD and provides a regulated posi-
tive output voltage. These outputs use external Schottky
diodes and capacitor multiplier stages (dependent upon
the required output voltage) to regulate up to ±30V.
Integrated soft-start circuitry minimizes the start-up
inrush current and eliminates output voltage overshoot
across the full input voltage range and all load condi-
tions. A constant switching frequency of 1.3MHz mini-
mizes output ripple and capacitor size.
White LED Backlight Applications
The AAT2822 consists of a 1.3MHz fixed-frequency DC/
DC boost controller, and an integrated high voltage
MOSFET power switch. A high-voltage rectifier, power
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
inductor, output capacitor, and sense resistors are
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.
If the OVP input voltage is exceeded the WLED driver
continues to regulate at the OVP threshold.
Start
EN High
WLED Boost
Stop Switching
VWLED >V
OVP
No
Yes
Yes
No
Figure 1: WLED Driver Operation.
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.
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Start
EN High
MAIN BOOST
VFB > FB Fault Trip
Level and Persist
NEGATIVE CP
VFBN >FBN Fault Trip
Level and Persist
POSITIVE CP
VFBP >FBP Fault Trip
Level and Persist
Start- Up Sequence
Complete
Shut-Down Main Boost,
Negative CP, and
Positive CP
Yes
No
Yes
Yes
Yes
No
No
No
No EN Low
OPAMP
Figure 2: Startup Sequence for AAT282X-11.
1. For AAT282x the startup sequence is positive charge pump followed by the nega-
tive charge pump.
Application Information
Main Step-Up Converter
Output Capacitor
The high output ripple inherent in the boost converter
necessitates low impedance output filtering. Multi-layer
ceramic (MLC) capacitors provide small size and ade-
quate capacitance, low parasitic equivalent series resis-
tance (ESR) and equivalent series inductance (ESL), and
are well suited for use with the primary step-up con-
verter. MLCs of type X7R or X5R are recommended to
ensure good capacitance stability over the full operating
temperature range.
The output capacitor is sized to maintain the output load
without significant voltage droop during the power
switch ON interval, when the output diode is not con-
ducting. And because the VGH, VGL also have their input
power from the main step-up converter output, the out-
put capacitor may also decrease the inrush current dur-
ing VGH and VGL start up. A ceramic output capacitor
with a minimum value of 22µF is recommended. For
inrush current sensitive applications, two 22µF are rec-
ommended. Typically, 25V rated ceramic capacitors are
required for the 24V boost output. Ceramic capacitors
sized as small as 0805 are available which meet these
requirements. MLCs exhibit significant capacitance
reduction with applied voltage. Output ripple measure-
ments should confirm that output voltage droop is
acceptable.
Input Capacitor
The boost converter input current flows during both ON
and OFF switching intervals. The input ripple current is
less than the output ripple and, as a result, less input
capacitance is required. However, the AAT2822 input
voltage is shared among other channels; a ceramic input
capacitor from 4.7µF to 10µF is recommended. Minimum
6.3V rated ceramic capacitors are required at the input.
Ceramic capacitors sized as small as 0603 are available
which meet these requirements.
Large capacitance tantalum or solid-electrolytic capaci-
tors may be necessary to meet stringent output ripple
and transient load requirements. These can replace (or
be used in parallel with) ceramic capacitors. Both tanta-
lum and OSCON-type capacitors are suitable due to their
low ESR and excellent temperature stability (although
they exhibit much higher ESR than MLCs). Aluminum-
electrolytic types are less suitable due to their high ESR
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characteristics and temperature drift. Unlike MLCs, these
types are polarized and proper orientation on input and
output pins is required. 30% to 70% voltage derating is
recommended for tantalum capacitors.
Selecting the Schottky Diode
To ensure minimum forward voltage drop and no recov-
ery, high voltage Schottky diodes are the best choice for
the primary step-up converter. The output diode is sized
to maintain acceptable efficiency and reasonable operat-
ing junction temperature under full load operating condi-
tions. Forward voltage (VF) and package thermal resis-
tance (θJA) are the dominant factors to consider in select-
ing a diode. The diode’s published current rating may not
reflect actual operating conditions and should be used
only as a comparative measure between similarly rated
devices. 20V rated Schottky diodes are recommended for
outputs less than 15V, while 30V rated Schottky diodes
are recommended for outputs greater than 15V.
The average diode current is equal to the output cur-
rent:
I
AVG
< I
OUT
The average output current multiplied by the forward
diode voltage determines the loss of the output diode.
P
LOSS_DIODE
= I
AVG
· V
F
= I
OUT
· V
F
Diode junction temperature can be estimated:
T
J
= T
A
+ θ
JA
· P
LOSS_DIODE
The junction temperature should be maintained below
110°C, but may vary depending on application and/or
system guidelines. The diode θJA can be minimized with
additional PCB area on the cathode. PCB heat sinking the
anode may degrade EMI performance.
The reverse leakage current of the rectifier must be con-
sidered to maintain low quiescent (input) current and
high efficiency under light load. The rectifier's reversed
current increases dramatically at high temperatures.
Selecting the Main Step-Up Inductor
The primary step-up converter is designed to operate
with a 2.2μH inductor for all input and output voltage
combinations. The inductor saturation current rating
should be greater than the NMOS current limit. If neces-
sary, the peak inductor current can exceed the satura-
tion level by a small amount with no significant effect on
performance. The maximum duty cycle can be estimated
from the relationship for a continuous mode boost con-
verter. Maximum duty cycle (DMAX) is the duty cycle at
minimum input voltage (VIN(MIN)).
DMAX =
(V
OUT
+ V
F
- V
IN(MIN)
)
VOUT + VF
Where VF is the Schottky diode forward voltage and can
be estimated at 0.5V. Manufacturer’s specifications list
both the inductor DC current rating, which is a thermal
limitation, and peak inductor current rating, which is
determined by the saturation characteristics.
Measurements at full load and high ambient temperature
should be completed to ensure that the inductor does
not saturate or exhibit excessive temperature rise.
The output inductor (L) is selected to avoid saturation at
minimum input voltage, maximum output load condi-
tions. Peak current may be calculated from the following
equation, again assuming continuous conduction mode.
Worst-case peak current occurs at minimum input volt-
age (maximum duty cycle) and maximum load. Switching
frequency (Fs) is at 1.3MHz with a 2.2µH inductor.
IPEAK = +
I
OUT
1 - DMAX
D
MAX
· V
IN(MIN)
2 · FS · L
The RMS current flowing through the boost inductor is
equal to the DC plus AC ripple components.
Under worst-case RMS conditions, the current waveform
is critically continuous. The resulting RMS calculation
yields worst-case inductor loss. The RMS value should be
compared against the manufacturer’s temperature rise
or thermal derating guidelines.
I
PEAK
3
IRMS =
For a given inductor type, smaller inductor size leads to
an increase in DCR winding resistance and, in most
cases, increased thermal impedance. Winding resistance
degrades boost converter efficiency and increases the
inductor operating temperature.
PLOSS_INDUCTOR = IRMS2 · DCR
Setting the Output Voltage
The resistive divider network R2 and R3 of Figure 7 pro-
grams the output to regulate at a voltage higher than
0.6V as shown in Table 1. To limit the bias current
required for the external feedback resistor string while
maintaining good noise immunity, the minimum sug-
AAT2822/2823/2824/2825
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gested value for R3 is 6.04kΩ. The resistive divider can
be calculated in the following equation:
R3 = R2 · -1 = R2 · - 1
VAVDD
VFB
VAVDD
0.6V
VAVDD (V)
R3 = 6.04kΩ
R2 (kΩ)
R3 = 59kΩ
R2 (MΩ)
9 84.5 0.825
10 93.1 0.931
11 105 1.02
12 115 1.13
13 124 1.21
15 143 1.4
20 196 1.1
22 215 2.1
24 237 2.3
Table 1: Setting the Output Voltage
for the Main Step-Up Converter.
Selecting Compensation Components
The AAT2822 main boost architecture uses peak current
mode control to eliminate the double pole effect of the
output L&C filter and simplifies compensation loop
design. The current mode control architecture simplifies
the transfer function of the control loop to a one-pole,
one left plane zero and one right half plane (RHP) sys-
tem in frequency domain. The dominant pole can be
calculated by:
fP =
1
2π · RO · C6
The ESR zero of the output capacitor can be calculated
by:
fZ_ESR =
1
2π · RESR · C6
Where:
C6 is the output filter capacitor
RO is the load resistor value
RESR is the equivalent series resistance of the output
capacitor.
The right half plane (RHP) zero can be determined by:
fZ_RHP = VIN2
2π · L1 · IAVDD · VAVDD
It is recommended to design the bandwidth to one
decade lower than the frequency of RHP zero to guaran-
tee the loop stability. A series capacitor and resistor
network (R11 and C8) connected to the COMP pin sets
the pole and zero which are given by:
fP_COM =
1
2π · REA · C8
fZ_COM =
1
2π · R11 · C8
Where:
C8 is the compensation capacitor
R11 is the compensation resistor
REA is the output resistance of the error amplifier (MΩ).
A 100pF capacitor and a 200kΩ resistor in series are
chosen for optimum phase margin and fast transient
response.
Charge Pump
The number of charge pump stages required for a given
output (VGH) varies with the input voltage applied (VAVDD)
from the main boost. A lower input voltage requires
more stages for a given output. If the numbers of stag-
es increases, the maximum load current limitation of the
charge pump would be decreased to maintain output
voltage regulation.
The number of stages required can be estimated by:
V
GH
- V
AVDD(MIN)
VAVDD(MIN) - 2VF
nP =
for the positive output and
V
GL
2VF - VAVDD(MIN)
nN =
for the negative output where VF = 0.31V is the forward
voltage of the BAT54 Schottky diode at 4mA forward
current.
When solving for np and nn, round up the solution to the
next highest integer to determine the number of stages
required.
Negative Output Voltage (VGL)
The negative output voltage is adjusted by a resistive
divider from the output (VON) to the FBN and REF pins.
The maximum reference voltage current is 200µA;
therefore, the minimum allowable value for R10 of Figure
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6 is 6.04kΩ. It is best to select the smallest value pos-
sible for R10, as this will keep the value of R9 to a mini-
mum. With R10 selected, R9 can be determined:
R9 = · R10 = · R10
V
GL
VREF
V
GL
1.2V
Positive Output Voltage (VGH)
The positive output voltage is set by a resistive divider
from the output (VGH) to the FBP and ground pins.
Limiting the value of R7 to 6.04kΩ or lower reduces noise
in the feedback circuit.
Once R7 has been determined, solve for R6:
R6 = R7 · - 1 = R7 · - 1
VGH
VFBP
VGH
0.6V
Flying and Output Capacitors
The minimum value for the flying capacitor is limited by
the output power requirement, while the maximum value
is set by the bandwidth of the power supply. If CFLY is too
small, the output may not be able to deliver the power
demanded, while too large of a capacitor may limit the
bandwidth and time required to recover from load and
line transients. A 0.1µF X7R or X5R ceramic capacitor is
typically used. The voltage rating of the flying and reser-
voir output capacitors varies with the number of charge
pump stages. The reservoir output capacitor value should
be roughly 10 times the value of the flying capacitor. Use
larger capacitors for reduced output ripple.
Input Capacitor
The primary function of the input capacitor is to provide
a low impedance loop for the edges of pulsed current
drawn by the IC. A low ESL X7R or X5R type ceramic
capacitor is ideal for this function. The size required will
vary depending on the load, output voltage, and input
voltage characteristics. Typically, the input capacitor
value should be 5 to 10 times the value of the flying
capacitor. If the source impedance of the input supply is
high, a larger capacitor may be required. To minimize
stray inductance, the capacitor should be placed as
closely as possible to the IC. This keeps the high fre-
quency content of the input current localized, minimizing
radiated and conducted EMI.
Rectifier Diodes
For the rectifiers, use Schottky diodes with a voltage rat-
ing of 1.5 times the input voltage. The maximum steady-
state voltage seen by the rectifier diodes for both the
positive and negative charge pumps (regardless of the
number of stages) is:
V
REVERSE
= V
IN
- V
F
The BAT54SDW quad Schottky diode in a SOT363
(2x2mm) package is a good choice for multiple-stage
charge pump configuration.
White LED Driver
The white LED backlight driver can be enabled when input
supply rises above under voltage lockout threshold. To
reduce inrush current it is recommended that the main
boost and white LED driver are not enabled concurrently.
Over-Voltage Protection (OVP)
with Open Circuit Failure
The OVP protection circuit consists of a resistor network
tied from the output voltage to the OVP pin (see Figure
3). To protect the device from open circuit failure, the
resistor divider can be selected such that the over-volt-
age threshold occurs prior to the output reaching
VLED+(MAX). The value of R5 should be selected from 10kΩ
to 20kΩ to minimize losses without degrading noise
immunity.
R4 = R5 · -1 = 10kΩ · -1
V
LED+(MAX)
VOVP
V
LED+(MAX)
0.6V
WLX
OVP
WFB
R8
C4
C5
D2
L
2
R4
R5
0.6V
0.3V
VIN
VWLX
VLED
Figure 3: Over-Voltage Protection Circuit.
OVP Constant Voltage Operation
Under closed loop constant current conditions, the output
voltage is determined by the operating current, LED for-
ward voltage characteristics (VFLED), quantity of series
connected LEDs (N), and the feedback pin voltage (VFB).
V
OUT
= V
FB
+ N · V
FLED
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When the rising OVP threshold is exceeded, switching is
stopped and the output voltage decays. Switching auto-
matically restarts when the output drops below the
lower OVP hysteresis voltage (100mV typical), and as a
result the output voltage increases. The cycle repeats,
maintaining an average DC output voltage proportional
to the average of the rising and falling OVP levels (mul-
tiplied by the resistor divider scaling factor). High oper-
ating frequency and low output voltage ripple ensure DC
current and negligible flicker in the LED string(s).
While OVP is active, the maximum LED current program-
ming error (ΔILED) is proportional to voltage error across
an individual LED (ΔVFLED).
∆VFLED =
N · V
FLED(TYP)
- V
OVP(MIN)
- V
WFB
N
To minimize the ΔILED error, the minimum OVP voltage
(VOVP(MIN)) may be increased, yielding a corresponding
increase in the maximum OVP voltage (VOVP(MAX)).
Measurements should confirm that the maximum switch-
ing node voltage (VWLX(MAX)) is less than 30V under worst
case operating conditions.
VWLX(MAX) = VOVP(MAX) · + 1 + VF + VRING
R
2
R1
VF is the Schottky diode D2 forward voltage at turn-OFF.
VRING is the voltage ring occurring at turn-OFF.
White LED Selection and Current Setting
The WLED current is controlled by the WFB voltage and
the ballast resistor (R8). For maximum accuracy, a 1%
tolerance resistor is recommended.
The ballast resistor (R8) value can be calculated as fol-
lows:
R8 =
V
WFB(MAX)
ILED(MAX)
Where VWFB = 0.3V
For example, if the maximum current for each string of
3 series LEDs is 20mA, the maximum current for a 10
inch panel (3S13P) is 260mA (20mA x 13), which cor-
responds to a minimum resistor value of 1.15Ω
R8 =
=
1.15Ω
0.3V
260mA
Maximum ILED Current (mA) R8(Ω)
30 0.768
25 0.909
20 1.15
15 1.54
10 2.32
5 4.64
Table 2: Maximum LED Current and Ballast
Resistor (R8) Values for 10” Panel Size.
Typical white LEDs are driven at maximum continuous
currents of 15mA to 20mA. The maximum number of
series-connected LEDs is determined by the minimum
output voltage of the boost converter (VLED), minus the
maximum feedback voltage (VWFB(MAX)) divided by the
maximum LED forward voltage (VFLED(MAX)) which can be
estimated from the manufacturers’ datasheet at the
maximum LED operating current.
VLED = VOVP(TYP) · + 1
R5
R4
N =
V
OVP(MIN)
- V
WFB(MAX)
VFLED(MAX)
For example, the typical forward voltage of the white
LED is 3.5V at 20mA.
VLED = VOVP(TYP) · = 0.6V · = 27.8V+ 1
R
5
R4
+ 1
464kΩ
10kΩ
N = = = 7.8 LEDs
V
OVP(MIN)
- V
WFB(MAX)
VFLED(MAX)
27.8V - 0.6V
3.5V
Therefore, under these typical operating conditions, 7
LEDs can be used in series for each string.
PWM Dimming Control
The dimming of the white LED can be controlled using a
PWM or a filter PWM signal. By connecting a PWM signal
to the WDIM pin and adjusting the duty cycle of the PWM
signal, the dimming of the white LED changes proportion-
ally to the percentage of the duty cycle as shown in Figure
4. However, the dimming control using PWM connected to
the WDIM pin can operate at a frequency up to 1kHz.
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WDIM 24
WLX
1
WCOMP 19
EN
9AGND 23
PGND2
2
WEN
FBP
10 OVP 21
DRVP
8VDD
7
WFB 20
N/C 16
N/C 15
PGND1
11
LX
12
COMP 13
FB 14
N/C 17
N/C 18
VIN 22
3
FBN
DRVN
AAT2822
adj
R8
R21
0
PWM
Figure 4: PWM Dimming Control.
For applications requiring a PWM frequency higher than
1KHz, an external filter PWM is connected to the WFB pin
to control the dimming of the white LED. This low-pass
filter (R23/C25) integrates the high frequency PWM signal
to produce a DC dimming control as shown in Figure 5.
WDIM 24
WLX
1
WCOMP 19
EN
9AGND 23
PGND2
2
WEN
FBP
10 OVP 21
DRVP
8VDD
7
WFB 20
N/C 16
N/C 15
PGND1
11
LX
12
COMP 13
FB 14
N/C 17
N/C 18
VIN 22
3
FBN
DRVN
AAT2822
adj
R8
4.99k
R21
HF-PWM
R23
4.99k
R22
28k
C25
0.1µF
Connect WDIM to VIN
Figure 5: Low-Pass Filter PWM Dimming Control.
When the PWM duty cycle is adjusted, the DC voltage
across the ballast resistor (R8) changes, resulting in
change of the white LED current. Apply the KCL at the
feedback node (WFB). The voltage across the R8 resistor
can be expressed:
R
21
R22
VR8 = 0.3V - · (VC25 - 0.3V)
For minimum dimming, VR8 = 0V.
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Choose R21 = 4.99kΩ and VC25 = 2V, and solve for R22:
R
21
(0.3V - VR8) · (VC25 - 0.3V)
R22 = = 28kΩ
The low-pass filter should be chosen to produce an
acceptable ripple for the DC dimming voltage and a
small time constant. For application where the PWM fre-
quency is greater than 10KHz, the optimum values for
the low-pass filter are R23 = 4.99kΩ and C25 = 0.1µF.
Selecting the Schottky Diode
To ensure minimum forward voltage drop and no recov-
ery, high-voltage Schottky diodes are considered the
best choice for the WLED boost converter. The output
diode is sized to maintain acceptable efficiency and rea-
sonable operating junction temperature under full load
operating conditions. Forward voltage (VF) and package
thermal resistance (θJA) are the dominant factors to con-
sider in selecting a diode. The diode's non-repetitive
peak forward surge current rating (IFSM) should be con-
sidered for high pulsed load applications such as camera
flash. The IFSM rating drops with increasing conduction
period. Manufacturers’ datasheets should be consulted
to verify reliability under peak load conditions. The
diode’s published current rating may not reflect actual
operating conditions and should be used only as a com-
parative measure between similarly rated devices.
40V rated Schottky diodes are recommended for outputs
less than 30V, while 60V rated Schottky diodes are rec-
ommended for outputs greater than 35V.
The average diode current is equal to the output cur-
rent:
I
AVG
= I
OUT
The average output current multiplied by the forward
diode voltage determines the loss of the output diode.
P
LOSS_DIODE
= I
AVG
· V
F
= I
OUT
· V
F
Diode junction temperature can be estimated:
T
J
= T
A
+ θ
JA
· P
LOSS_DIODE
Output diode junction temperature should be maintained
below 110°C, but may vary depending on application
and/or system guidelines. The diode θJA can be mini-
mized with additional PCB area on the cathode. PCB
heat-sinking the anode may degrade EMI performance.
The reverse leakage current of the rectifier must be con-
sidered to maintain low quiescent (input) current and
high efficiency under light load. The rectifier's reverse
current increases dramatically at elevated temperatures.
Selecting the WLED Step-Up Inductor
The WLED step-up converter has the same topology as
the main step-up converter. It is designed to operate
with a 2.2μH inductor for all input and output voltage
combinations. The inductor saturation current rating
should be greater than the NMOS current limit.
DMAX =
(V
OUT
+ V
F
- V
IN(MIN)
)
VOUT + VF
The output inductor (L) is selected to avoid saturation at
minimum input voltage and maximum output load con-
ditions. Peak current may be calculated from the follow-
ing equation, again assuming continuous conduction
mode. Worst-case peak current occurs at minimum input
voltage (maximum duty cycle) and maximum load.
Switching frequency is estimated at 1.3MHz with a
2.2µH inductor.
IPEAK = +
I
OUT
1 - DMAX
D
MAX
· V
IN(MIN)
2 · FS · L
Selecting the WLED Step-Up Capacitors
The high output ripple inherent in the boost converter
necessitates low impedance output filtering.
Multi-layer ceramic (MLC) capacitors provide small size
and adequate capacitance, low parasitic equivalent
series resistance (ESR) and equivalent series inductance
(ESL), and are well suited for use with the WLED boost
regulator. MLC capacitors of type X7R or X5R are recom-
mended to ensure good capacitance stability over the
full operating temperature range.
The output capacitor is sized to maintain the output load
without significant voltage droop (ΔVOUT) during the
power switch ON interval, when the output diode is not
conducting. A ceramic output capacitor with a value of
2.2μF to 4.7μF is recommended. Typically, 50V rated
capacitors are required for the 28V maximum boost out-
put. Ceramic capacitors sized as small as 0805 or 1206
are available which meet these requirements.
MLC capacitors exhibit significant capacitance reduction
with applied voltage. Output ripple measurements
should confirm that output voltage droop and operating
stability are acceptable. Voltage derating can minimize
this factor, but results may vary with package size and
among specific manufacturers.
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The output capacitor size can be estimated using the
equation:
I
OUT
· D
MAX
FS · ∆VOUT
COUT =
To maintain stable operation at full load, the output
capacitor should be sized to maintain ΔVOUT between
100mV and 200mV.
The WLED boost converter input current flows during
both ON and OFF switching intervals. The input ripple
current is lower than the output ripple and, as a result,
a lower input capacitance is required.
LCD VCOM Buffer
The VCOM buffer is designed to drive the voltage on the
backplane of an LCD display. The buffer must be capable
of sinking and sourcing capacitive pulse current at low
frequency. A 10nF ceramic output capacitor in series
with a 100Ω resistor is sufficient for buffer stability at
high frequencies.
The VCOM output voltage is typically set to half of the
main boost output voltage VADD. The maximum input bias
voltage for the VCOM buffer (VOPIN) cannot exceed 13V. In
applications where the main boost output voltage VVADD is
greater than 13V, VOPIN should be connected to an exter-
nal supply to prevent damage to the device; the jumper
J7 should be left open to disconnect VAVDD from VOPIN.
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
21
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
D1
100pF
C8
200kΩ
R11
4.7μF
10VC1
VIN
WDIM 24
WLX
1
WCOMP19
EN
9
AGND 23
PGND2
2
WEN
5
FBP
10 OVP21
DRVP
8
VDD
7
WFB20
OP+16
OPIN 15
PGND1
11
LX
12
COMP 13
FB 14
OP-17
OUT18
VIN22
REF
3
FBN
4
DRVN
6
U1
AAT2822
10μF
10V
C3
0.22μF
6.3V
C7
0.1μF
25V
C12
0.22μF
50V
C21
PWM
2.2μH
L2
Adj
R2
6.04kΩ
R3
22μF
25V
C6
8nF
C9
D2
2.2μF
50V
C5
adj
R4
10kΩ
R5
6.04kΩ
R10
Adj
R6
6.04kΩ
R7
10kΩ
R14
10kΩ
R13
17.4kΩ
R12
0Ω
R1 adj
R8
0.1μF
50V
C13
0.22μF
25V
C18
0.1μF
50V
C11
0.1μF
25V
C10
0.22μF
25V
C16
0.22μF
50V
C19
0.22μF
50V
C17
J1
VIN
EN
LX
VAVDD
VGH (positive)
VGL (negative)
J2
VIN
J3
WEN
Adj
R9
0.1μF
10VC2
WLX
10μF
16V
C4
2.2μH
L1
OVP
OVP
0Ω
R15
AGND
VDD
3 4
5
6
2
1
A1
BAT54SDW
VDD
open
R16
34
5
6
2
1
A2
BAT54SDW
0.1μF
50V
C14
0.1μF
50V
C15
34
5
6
2
1
A3
BAT54SDW
0.22μF
50V
C20
1
2
stage 3
J5
1
2
stage4
J6
0.1μF
C22
DRVN
DRVP
FBP
FBN
0.1μF
25V
C23
100Ω
R17
10nF
C24
1
2
stage 2
J4
VIN
VIN-WLED
open
R19
0Ω
R18
VAVDD
0Ω
R21
VIN
0Ω
R20
HF-PWM
open
R23
open
R22
WFB
open
C25
3 4
5
6
2
1
A4
BAT54SDW
0.1μF
50V
C27
0.1μF
50V
C28
1
2
stage2
J8
1
2
stage3
J9
1
2
stage4
J10
0.22μF
50V
C29
0.22μF
50V
C30
AVDD
VIN
VOPIN
1
2
J7
10pF
25V
C26
WLED+
WLED-
1.2V
0.6V
0.6V
0.6V
0V
Figure 6: AAT2822IBK Evaluation Board Schematic.
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
22 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Component Part Number Description Manufacturer
U1 AAT2822IBK TFT-LCD DC-DC Converter with WLED
Driver and VCOM Buffer Skyworks
C1 GRM188R61A475K CAP CERAMIC 4.7μF 0603 X5R 10V 10%
Murata
C2 GRM188R71C104K CAP CERAMIC 0.1μF 0603 X7R 16V 10%
C3, C4 GRM21BR61C106K CAP CERAMIC 10μF 0805 X5R 16V 10%
C5 GRM31CR71H225K CAP CERAMIC 2.2μF 1206 X7R 50V 10%
C6 GRM31CR61C226M CAP CERAMIC 22μF 1206 X5R 16V 20%
C7 GRM188R71A224K CAP CERAMIC 0.22μF 0603 X7R 10V10%
C8 GRM1885C1H101J CAP CERAMIC 100pF 0603 COG 50V 5%
C9 GRM2195C1H822J CAP CERAMIC 8nF 0805 X7R 50V 10%
C10, C12, C22, C23 GRM188R61E104K CAP CERAMIC 0.1μF 0603 X5R 25V 10%
C11, C13, C14,
C15, C27, C28 GRM188R71H104K CAP CERAMIC 0.1μF 0603 X7R 50V 10%
C16, C18 GRM188R61E224K CAP CERAMIC 0.22μF 0603 X5R 25V10%
C17, C19, C20,
C21, C29, C30 GRM21BR71H224K CAP CERAMIC 0.22μF 0805 X7R 50V10%
C24 GRM188R71H103K CAP CERAMIC 10nF 0603 X7R 50V 10%
C25 NC
C26 GRM1885C1H100J CAP CERAMIC 10pF 0603 COG 50V 5%
A1, A2, A3, A4 BAT54SDW-7-F Schottky Diode Array 30V SC70-6 Diode Inc
D1, D2 SS16L Schottky Diode 1A 60V Micro SMP Taiwan Semiconductor
L1, L2 CDRH5D16-2R2 POWER INDUCTOR 2.2μH 3.0A SMD Sumida
R2, R4, R6, R8, R9 Adjustable Value (See Equations.1 – 5
and Table 5); 0603
Yageo
R3, R7, R10 RC0603FR-0760K4L Res 6.04kΩ 1/10W 1% 0603 SMD
R5, R13, R14 RC0603FR-0710KL Res 10kΩ 1/10W 1% 0603 SMD
R11 RC0603FR-07200KL Res 200kΩ 1/10W 1% 0603 SMD
R12 RC0603FR-0717K4L Res 17.4kΩ 1/10W 1% 0603 SMD
R15, R19, R20, R21 RC0603FR-070RL Res 0Ω 1/10W 1% 0603 SMD
R17 RC0603FR-07100RL Res 100Ω 1/10W 1% 0603 SMD
R18, R22, R23, R25 NC
Table 3: AAT2822IBK Evaluation Board Bill Of Materials (BOM).
Panel Sizes (inches) WLED Matrix (Series and Parallel) Ballast Resistor R8 (Ω)
5 3S5P 2.37
5.6 3S6P 2.0
7 3S9P 1.3
8 3S10P/11P 1.2
10 3S13P 1.0
5 7S2P 4.7
Table 4: Ballast Resistor Selection for Different Panel Sizes.
Eq. 1: R2 = R3 · -1 = 6.04kΩ · -1
VAVDD
VFB
VAVDD
0.6V
Eq. 2: R9 = · R10 = · 6.04kΩ
V
GL
VFBN
V
GL
1.2V
Eq. 3: R6 = R7 · - 1 = 6.04kΩ · - 1
VGH
VFBP
VGH
0.6V
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
23
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Eq. 4: R4 = R5 · -1 = 10kΩ · -1
V
LED+(MAX)
VOVP
V
LED+(MAX)
0.6V
Eq. 5: R8 = =
V
WFB(MAX)
ILED(MAX)
0.3V
ILED(MAX)
D1
100pF
C8
200kΩ
R11
4.7μF
10V C1
VIN
WDIM 24
WLX
1
WCOMP 19
EN
9
AGND 23
PGND2
2
WEN
5
FBP
10 OVP 21
DRVP
8
VDD
7
WFB 20
N/C 16
N/C 15
PGND1
11
LX
12
COMP 13
FB 14
N/C 17
N/C 18
VIN22
REF
3
FBN
4
DRVN
6
U1
AAT2823
10μF
10V
C3
0.22μF
6.3V
C7
0.1μF
25V
C12
0.22μF
50V
C21
PWM
2.2μH
L2
Adj
R2
6.04kΩ
R3
22μF
25V
C6
8nF
C9
D2
2.2μF
50V
C5
adj
R4
10kΩ
R5
6.04kΩ
R10
Adj
R6
6.04kΩ
R7
17.4kΩ
R12
0Ω
R1 adj
R8
0.1μF
50V
C13
0.22μF
25V
C18
0.1μF
50V
C11
0.1μF
25V
C10
0.22μF
25V
C16
0.22μF
50V
C19
0.22μF
50V
C17
J1
VIN
EN
LX
VAVDD
VGH (positive)
VGL (negative)
J2
VIN
J3
WEN
Adj
R9
0.1μF
10V C2
WLX
10μF
16V
C4
2.2μH
L1
OVP
OVP
AGND
VDD
34
5
6
2
1
A1
BAT54SDW
VDD
34
5
6
2
1
A2
BAT54SDW
0.1μF
50V
C14
0.1μF
50V
C15
34
5
6
2
1
A3
BAT54SDW
0.22μF
50V
C20
1
2
stage 3
J5
1
2
stage4
J6
DRVN
DRVP
FBP
FBN
0.1μF
25V
C23
1
2
stage 2
J4
VIN
VIN-WLED
open
R19
0Ω
R18
VAVDD
0Ω
R21
VIN
0Ω
R20
HF-PWM
open
R23
open
R22
WFB
open
C25
3 4
5
6
2
1
A4
BAT54SDW
0.1μF
50V
C27
0.1μF
50V
C28
1
2
stage2
J8
1
2
stage3
J9
1
2
stage4
J10
0.22μF
50V
C29
0.22μF
50V
C30
AVDD
VIN
10pF
25V
C26
WLED+
WLED-
1.2V
0.6V
0.6V
0.6V
0V
Figure 7: AAT2823IBK Evaluation Board Schematic.
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
24 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
D1
100pF
C8
200kΩ
R11
4.7μF
10VC1
VIN
N/C24
N/C
1
N/C19
EN
9
AGND 23
PGND2
2
WEN
5
FBP
10 N/C21
DRVP
8
VDD
7
N/C20
OP+16
OPIN 15
PGND1
11
LX
12
COMP 13
FB 14
OP-17
OUT18
VIN22
REF
3
FBN
4
DRVN
6
U1
AAT2824
10μF
10V
C3
0.22μF
6.3V
C7
0.1μF
25V
C12
0.22μF
50V
C21
Adj
R2
6.04kΩ
R3
22μF
25V
C6
6.04kΩ
R10
Adj
R6
6.04kΩ
R7
10kΩ
R14
10kΩ
R13
0Ω
R1
0.1μF
50V
C13
0.22μF
25V
C18
0.1μF
50V
C11
0.1μF
25V
C10
0.22μF
25V
C16
0.22μF
50V
C19
0.22μF
50V
C17
J1
VIN
EN
LX
VAVDD
VGH (positive)
VGL (negative)
J2
VIN
WEN
Adj
R9
0.1μF
10VC2
2.2μH
L1
0Ω
R15
AGND
VDD
3 4
5
6
2
1
A1
BAT54SDW
VDD
open
R16
34
5
6
2
1
A2
BAT54SDW
0.1μF
50V
C14
0.1μF
50V
C15
34
5
6
2
1
A3
BAT54SDW
0.22μF
50V
C20
1
2
stage 3
J5
1
2
stage4
J6
0.1μF
C22
DRVN
DRVP
FBP
FBN
0.1μF
25V
C23
100Ω
R17
10nF
C24
1
2
stage 2
J4
VIN
open
R19
0Ω
R18
VAVDD
3 4
5
6
2
1
A4
BAT54SDW
0.1μF
50V
C27
0.1μF
50V
C28
1
2
stage2
J8
1
2
stage3
J9
1
2
stage4
J10
0.22μF
50V
C29
0.22μF
50V
C30
AVDD
VIN
VOPIN
1
2
J7
10pF
25V
C26
1.2V
0.6V
0.6V
0V
Figure 8: AAT2824IBK Evaluation Board Schematic.
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
25
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
D1
100pF
C8
200kΩ
R11
4.7μF
10VC1
VIN
N/C 24
N/C
1
N/C19
EN
9
AGND 23
PGND2
2
WEN
5
FBP
10 N/C21
DRVP
8
VDD
7
N/C20
N/C 16
N/C 15
PGND1
11
LX
12
COMP 13
FB 14
N/C 17
N/C 18
VIN 22
REF
3
FBN
4
DRVN
6
U1
AAT2825
10μF
10V
C3
0.22μF
6.3V
C7
0.1μF
25V
C12
0.22μF
50V
C21
Adj
R2
6.04kΩ
R3
22 μF
25V
C6
6.04kΩ
R10
Adj
R6
6.04kΩ
R7
0Ω
R1
0.1μF
50V
C13
0.22μF
25V
C18
0.1μF
50V
C11
0.1μF
25V
C10
0.22μF
25V
C16
0.22μF
50V
C19
0.22μF
50V
C17
J1
VIN
EN
LX
VAVDD
VGH (positive)
VGL (negative)
J2
VIN
WEN
Adj
R9
0.1μF
10VC2
2.2μH
L1
AGND
VDD
3 4
5
6
2
1
A1
BAT54SDW
VDD
34
5
6
2
1
A2
BAT54SDW
0.1μF
50V
C14
0.1μF
50V
C15
34
5
6
2
1
A3
BAT54SDW
0.22μF
50V
C20
1
2
stage 3
J5
1
2
stage4
J6
DRVN
DRVP
FBP
FBN
0.1μF
25V
C23
1
2
stage 2
J4
VIN
open
R19
0Ω
R18
VAVDD
3 4
5
6
2
1
A4
BAT54SDW
0.1μF
50V
C27
0.1μF
50V
C28
1
2
stage2
J8
1
2
stage3
J9
1
2
stage4
J10
0.22μF
50V
C29
0.22μF
50V
C30
AVDD
VIN
10pF
25V
C26
1.2V
0.6V
0.6V
0V
Figure 9: AAT2825IBK Evaluation Board Schematic.
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
26 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Figure 10: AAT28XXIBK Evaluation Board Figure 11: AAT28XXIBK Evaluation Board
Top Side Layout. Bottom Side Layout.
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
27
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
Ordering Information1,2
Package Part Marking1Part Number (Tape and Reel)2
TQFN44-24 8XXYY AAT2822IBK-T1
TQFN44-24 F8XYY AAT2822IBK-1-T1
TQFN44-24 B7XYY AAT2823IBK-T1
TQFN44-24 F9XYY AAT2823IBK-1-T1
TQFN44-24 AAT2824IBK-T1
TQFN44-24 AAT2824IBK-1-T1
TQFN44-24 AAT2825IBK-T1
TQFN44-24 AAT2825IBK-1-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information3
TQFN44-24
4.000 ± 0.050
2.700 ± 0.050
Pin 1 Dot By Marking
4.000 ± 0.050 2.700 ± 0.050
0.214 ± 0.036
0.500 BSC 0.400 ± 0.050
0.750 ± 0.050
0.255 ± 0.025
Pin 1 Identification
Chamfer 0.300 ×
45
°
1
Top View Bottom View
Side View
0.000 − 0.050
All dimensions in millimeters.
AAT2822/2823/2824/2825
DATA SHEET
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
28 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202081B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a
service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Sky-
works may change its documentation, products, services, specications or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no
responsibility whatsoever for conicts, incompatibilities, or other difculties arising from any future changes.
No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided here-
under, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale.
THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR
PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES
NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, IN-
CLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM
THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or en-
vironmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper
use or sale.
Customers are responsible for their products and applications using Skyworks products, which may deviate from published specications as a result of design defects, errors, or operation of products outside of pub-
lished parameters or design specications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product
design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specications or parameters.
Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for
identication purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference.
