202289A.pdf

EVALUATION BOARD DATA SHEET
EV171
Evaluation Board for the AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Introduction
The AAT2868 EVAL board demonstrates the functionality of the AAT2868 and its application as a backlight driver with
dual LDO outputs.
The AAT2868 is a low-noise, constant-frequency charge pump DC/DC converter that uses a dual-mode load switch (1x)
and fractional (1.5x) conversion to maximize efficiency for white LED Content Adaptive Brightness Control (CABC)
applications. The AAT2868 is capable of driving 4 white LEDs at a total of 124mA and two 150mA low dropout (LDO)
linear regulators from a 2.7V to 5.5V input. All these functions can be programmed using the AS2Cwire™ interface.
Skyworks' AS2Cwire™ serial digital input is used to enable, disable and set the maximum LED current to one of 32
levels for the LEDs. Each LED current ranges from 31mA to 0.4mA. An external PWM input is adopted to dim the LED
current from 100% to 1% of the maximum LED current by varying the PWM duty cycle with frequencies up to 100kHz.
The AS2Cwire interface is also used to enable and disable LDOs and set the LDOs' output voltages. Five output voltage
levels and sixteen combinations of LDOA and LDOB can be set via the interface.
This document describes the AAT2868 evaluation board and its accompanying user interface. A brief “Getting Started”
section is also included to help the user to begin operating the evaluation board. The AAT2868 evaluation board is
shown in Figure 1; Figures 2 and 6 depict the board schematic and layout. Figure 4 illustrates the functions of the three
buttons on the EVAL board. For additional information, please consult the AAT2868 product datasheet.
Board Picture
(a) Top Side
(b) Bottom Side
Figure 1: AAT2868 Evaluation Board.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
1
EVALUATION BOARD DATA SHEET
EV171
Evaluation Board for the AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Evaluation Board Schematic
U1
AAT2868
C1
1µF
J1
1
18
7
6
DC+
V_LDO
CIN
2.2µF
DC-
8
5
AAT2868
White LED
Driver
R1
0
D1
FCAP
CF
56nF
EP
D1
D2
D3
D4
LDOA
LDOB
R2
0
R3
0
R4
0
D3
D2
10
11
12
13
3
D4
LDOA
2
LDOB
CLDOB
2.2µF
PWM
CLDOA
2.2µF
EN/SET
R10 R11 R12
1k 1k 1k
SELECT
R7
50k
VOUT
COUT
1µF
EN/SET
PWM
9
R8
50k
C2
1µF
16
15
17
GND
AGND
14
4
V _MCU
C2+
C2OUTCP
C1+
C1IN
INLDO
1
2
3
4
U2
VDD
GP5
GP4
GP3
PIC12F675
VSS
GP0
GP1
GP2
C3
0.1µF
8
7
6
5
R9
1k
LED2
Red
R6
1k
DETAIL
LED1
SEND
AS2Cwire
Microcontroller
Figure 2: AAT2868 Evaluation Board Schematic.
2
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
EVALUATION BOARD DATA SHEET
EV171
Evaluation Board for the AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
Getting Started
The board has two terminals labeled DC+ and DC- for the input power supply connection. Set J1 to the left position;
jump the V_MCU and apply 2.7V to 5.5V power to the DC+ and DC- terminals to power the AAT2868 (U1) and microcontroller (U2); the red LED (LED2) should illuminate when the microcontroller is powered. EN/SET option provides
access to the microcontroller program. Jump the EN/SET terminal when using microcontroller program to generate
AS2Cwire data for the AAT2868. Figure 3 shows the connection of the AAT2868 board.
Figure 3: AAT2868 Evaluation Board Demonstration Connection.
The three buttons on the AAT2868 evaluation board are used to set address and data for the registers and send the
selected address and data to the AAT2868 through the EN/SET signal line. Figure 4 shows the functions of the three
buttons.
Button Functions
Three buttons are located on the evaluation board: SELECT, DETAIL, and SEND. The SELECT button is used to select
a register address. Each press of the SELECT button selects a register address from 0 to 5 then wraps back to 0 (register address 1 is reserved and the processor program is designed to skip this address selection). The DETAIL button
is used to select data for a particular address register. The SEND button sends the selected address and data to the
EN/SET signal line. Details of the button functions are shown in Figure 4.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
3
EVALUATION BOARD DATA SHEET
EV171
Evaluation Board for the AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
SELECT
Button
DETAIL
Button
Pressed times Register Addr.
0
1
2
Backlight MSB
2
3
Backlight LSBs
3
4
LDO Enable/Disable
4
5
LDO Output Voltage
Selected Register
Addr. 0
Addr. 2
Three
Button
Functions
Addr.3
Addr. 4
Addr. 5
SEND
Button
Register Function
0
Backlight Enable
Pressed times
0
Detail selected
Backlighting Enable
1
Backlighting Disable
0
BL[4] = 0
1
BL[4] = 1
0
BL[3~0] = 0000
1
BL[3~0] = 0001
15
BL[3~0] = 1111
0
LDOA off, LDOB off
1
LDOA off, LDOB on
2
LDOA on, LDOB off
3
LDOA on, LDOB on
0
LDOA=3.0V LDOB=2.8V
1
LDOA=3.0V LDOB=1.8V
2
LDOA=3.0V LDOB=1.5V
3
LDOA=3.0V LDOB=1.2V
4
LDOA=2.8V LDOB=2.8V
5
LDOA=2.8V LDOB=1.8V
6
7
LDOA=2.8V LDOB=1.5V
LDOA=2.8V LDOB=1.2V
8
LDOA=1.8V LDOB=2.8V
9
LDOA=1.8V LDOB=1.8V
10
LDOA=1.8V LDOB=1.5V
11
LDOA=1.8V LDOB=1.2V
12
LDOA=1.5V LDOB=2.8V
13
LDOA=1.5V LDOB=1.8V
14
LDOA=1.5V LDOB=1.5V
15
LDOA=1.5V LDOB=1.2V
Send Selected Address and Data through EN/SET Signal Line
Figure 4: Button Functions of the AAT2868 Evaluation Board.
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
EVALUATION BOARD DATA SHEET
EV171
Evaluation Board for the AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
LED Current Control
AS2Cwire Interface
The LED current can be programmed from 0.4mA to 31mA with 32 steps via the AS2Cwire interface. Address 3 and 2
with 5 bits from BL[0] to BL[5] are used to set the LED current value as shown in Table 1.
Addr2
Addr3
LED Current Codes
BL4
BL3
BL2
BL1
BL0
LED Current (mA)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0.4
0.9
1.9
2.9
3.9
4.9
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0 [Default]
21.0
22.0
23.0
24.0
25.0
26.0
27.0
28.0
29.0
30.0
31.0
Table 1: AAT2868 Maximum LED Current Set Registers.
The LED current changes to the programmed value only after the “Backlight LSBs” register is written. For example, the
LED current settings can be reset from the default setting of 20mA to 31mA via the following steps:
1.
2.
3.
4.
5.
6.
Press
Press
Press
Press
Press
Press
the
the
the
the
the
the
SELECT button to select the Address 2 “Backlight MSB” register.
DETAIL button to set BL[4] to 1.
SEND button to send the selected address and data to AAT2868 via the EN/SET pin.
SELECT button to select Address 3 “Backlight LSBs” register.
DETAIL button to set BL[3~0] to 1111.
SEND button to set each LED's current to 31mA.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
5
EVALUATION BOARD DATA SHEET
EV171
Evaluation Board for the AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
PWM Interface
An external PWM signal with a frequency of 1kHz to 100kHz and duty cycle varying from 100% to 1% can be fed into
the AAT2868's PWM pin to dim the LED current from the programmed maximum value to 1% of maximum through the
PWM terminal on the board for CABC applications. Figure 5 shows an example of linear change of the LED current level
as the PWM duty cycle varies with the current level set to a maximum of 20mA.
22
20
18
ILED (V)
16
14
12
10
8
6
4
2
0
100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5
0
PWM Duty Cycle (%)
Figure 5: LED Current Dimming vs. PWM Duty Cycle
(Maximum Current = 20mA).
LDO Control
The AAT2868 includes two LDOs: LDOA and LDOB. The LDOs' enable, disable, and output voltage values are controlled
by writing register through AS2Cwire interface. Figure 4 shows how to use the three buttons on the evaluation board
to select and send LDO settings.
Printed Circuit Board
(a) Top Layer
(b) Bottom Layer
Figure 6: AAT2868 Evaluation Board Layout.
6
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
EVALUATION BOARD DATA SHEET
EV171
Evaluation Board for the AAT2868
CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators
AAT2868 EVAL Component List
Component
Part Number
Description
Manufacturer
U1
U2
R1, R2, R3, R4
R7, R8
R6, R9, R10, R11, R12
C1, C2, COUT
CIN, CLA, CLB
C3
CF
D1, D2, D3, D4
LED1
LED2
CYCLE,UP, DOWN
AAT2868IDT-T1
PIC12F675
RC0603FR-070RL
RC0603FR-0749K9L
RC0603FR-071KL
GRM188R71C105K
GRM188R61A225K
GRM188R71C104K
GRM188R71C563K
RS-0805UW
0805KGCT
0805KRCT
6*6*5
High Efficiency, 4 Channel Backlight Driver with Dual LDOs
8-Pin FLASH-Based 8-Bit CMOS Microcontroller
Res 0Ω 1/10W 1% 0603 SMD
Res 49.9KΩ 1/10W 1% 0603 SMD
Res 1KΩ 1/10W 1% 0603 SMD
Cap Ceramic 1μF 0603 X7R 16V 10%
Cap Ceramic 2.2μF 0603 X5R 10V 10%
Cap Ceramic 0.1µF 0603 X7R 16V 10%
Cap Ceramic 0.056μF 0603 X7R 16V 10%
20mA White LED 0805
Green LED 0805
Red LED 0805
12V 50mA Pushbutton
Skyworks
Microchip
Yageo
Murata
Realstar
HB
E-LT
Table 2: AAT2868 Evaluation Board Component List.
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202289A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 23, 2012
7