Evaluation Board for the AAT2868 CABC Compatible Four-Channel Backlight Driver with Dual LDO Regulators

Transcription

1 Introduction EVALUATION BOARD DATA SHEET The AAT88 EVAL board demonstrates the functionality of the AAT88 and its application as a backlight driver with dual LDO outputs. The AAT88 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 AAT88 is capable of driving white LEDs at a total of 1mA and two 15mA low dropout (LDO) linear regulators from a.7v to 5.5V input. All these functions can be programmed using the AS Cwire interface. Skyworks' AS Cwire serial digital input is used to enable, disable and set the maximum LED current to one of 3 levels for the LEDs. Each LED current ranges from 31mA to.ma. An external PWM input is adopted to dim the LED current from 1% to 1% of the maximum LED current by varying the PWM duty cycle with frequencies up to 1kHz. The AS Cwire 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 AAT88 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 AAT88 evaluation board is shown in Figure 1; Figures and depict the board schematic and layout. Figure illustrates the functions of the three buttons on the EVAL board. For additional information, please consult the AAT88 product datasheet. Board Picture (a) Top Side Figure 1: AAT88 Evaluation Board. (b) Bottom Side 1

2 Evaluation Board Schematic DC+ J1 C IN.µF C1 1µF V_LDO GND AGND DC- U1 AAT88 C1+ C1- IN INLDO C+ C- OUTCP C OUT 1µF C 1µF R1 D1 R R3 R D D3 D VOUT AAT88 White LED Driver V_MCU R8 5k EN/SET PWM R7 5k 1 9 C F 5nF EN/SET PWM FCAP EP D1 D D3 D LDOA LDOB C LDOB.µF LDOB C LDOA.µF LDOA SELECT R1 R11 R1 1k 1k 1k 1 3 U PIC1F75 VDD VSS GP5 GP GP GP1 GP3 GP C3.1µF R9 1k LED Red DETAIL SEND R 1k LED1 AS Cwire Microcontroller Figure : AAT88 Evaluation Board Schematic.

3 Getting Started EVALUATION BOARD DATA SHEET 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.7v to 5.5V power to the DC+ and DC- terminals to power the AAT88 (U1) and microcontroller (U); the red LED (LED) 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 AS Cwire data for the AAT88. Figure 3 shows the connection of the AAT88 board. Figure 3: AAT88 Evaluation Board Demonstration Connection. The three buttons on the AAT88 evaluation board are used to set address and data for the registers and send the selected address and data to the AAT88 through the EN/SET signal line. Figure shows the functions of the three buttons. 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 to 5 then wraps back to (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. 3

4 SELECT Pressed times Register Addr Register Function Backlight Enable Backlight MSB Backlight LSBs LDO Enable/Disable LDO Output Voltage Three Functions DETAIL Selected Register Addr. Pressed times Detail selected Backlighting Enable 1 Backlighting Disable Addr. BL[] = 1 BL[] = 1 Addr.3 BL[3~] = 1 BL[3~] = 1 15 BL[3~] = 1111 Addr. LDOA off, LDOB off 1 LDOA off, LDOB on LDOA on, LDOB off 3 LDOA on, LDOB on Addr. 5 LDOA=3.V LDOB=.8V 1 LDOA=3.V LDOB=1.8V LDOA=3.V LDOB=1.5V 3 LDOA=3.V LDOB=1.V LDOA=.8V LDOB=.8V 5 LDOA=.8V LDOB=1.8V LDOA=.8V LDOB=1.5V 7 LDOA=.8V LDOB=1.V 8 LDOA=1.8V LDOB=.8V 9 LDOA=1.8V LDOB=1.8V 1 LDOA=1.8V LDOB=1.5V 11 LDOA=1.8V LDOB=1.V 1 LDOA=1.5V LDOB=.8V LDOA=1.5V LDOB=1.8V LDOA=1.5V LDOB=1.5V LDOA=1.5V LDOB=1.V SEND Send Selected Address and Data through EN/SET Signal Line Figure : Functions of the AAT88 Evaluation Board.

5 LED Current Control AS Cwire Interface The LED current can be programmed from.ma to 31mA with 3 steps via the AS Cwire interface. Address 3 and with 5 bits from BL[] to BL[5] are used to set the LED current value as shown in Table 1. LED Current Codes Addr Addr3 BL BL3 BL BL1 BL LED Current (ma) [Default] Table 1: AAT88 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 ma to 31mA via the following steps: 1. Press the SELECT button to select the Address Backlight MSB register.. Press the DETAIL button to set BL[] to Press the SEND button to send the selected address and data to AAT88 via the EN/SET pin.. Press the SELECT button to select Address 3 Backlight LSBs register. 5. Press the DETAIL button to set BL[3~] to Press the SEND button to set each LED's current to 31mA. 5

6 PWM Interface EVALUATION BOARD DATA SHEET An external PWM signal with a frequency of 1kHz to 1kHz and duty cycle varying from 1% to 1% can be fed into the AAT88'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 ma. ILED (V) PWM Duty Cycle (%) Figure 5: LED Current Dimming vs. PWM Duty Cycle (Maximum Current = ma). LDO Control The AAT88 includes two LDOs: LDOA and LDOB. The LDOs' enable, disable, and output voltage values are controlled by writing register through AS Cwire interface. Figure shows how to use the three buttons on the evaluation board to select and send LDO settings. Printed Circuit Board (a) Top Layer Figure : AAT88 Evaluation Board Layout. (b) Bottom Layer

7 AAT88 EVAL Component List Component Part Number Description Manufacturer U1 AAT88IDT-T1 High Efficiency, Channel Backlight Driver with Dual LDOs Skyworks U PIC1F75 8-Pin FLASH-Based 8-Bit CMOS Microcontroller Microchip R1, R, R3, R RC3FR-7RL Res Ω 1/1W 1% 3 SMD R7, R8 RC3FR-79K9L Res 9.9KΩ 1/1W 1% 3 SMD Yageo R, R9, R1, R11, R1 RC3FR-71KL Res 1KΩ 1/1W 1% 3 SMD C1, C, COUT GRM188R71C15K Cap Ceramic 1μF 3 X7R 1V 1% CIN, CLA, CLB GRM188R1A5K Cap Ceramic.μF 3 X5R 1V 1% C3 GRM188R71C1K Cap Ceramic.1µF 3 X7R 1V 1% Murata CF GRM188R71C53K Cap Ceramic.5μF 3 X7R 1V 1% D1, D, D3, D RS-85UW ma White LED 85 Realstar LED1 85KGCT Green LED 85 LED 85KRCT Red LED 85 HB CYCLE,UP, DOWN **5 1V 5mA Pushbutton E-LT Table : AAT88 Evaluation Board Component List. Copyright 1 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. Skyworks may change its documentation, products, services, specifications 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 conflicts, incompatibilities, or other difficulties 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 hereunder, 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 environmental 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 specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. 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 specifications 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 identification purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at are incorporated by reference. 7