4393244ADM8845EB_prb| Application Note
Evaluation Board for Charge Pump Driver for LCD White LED Backlights
Preliminary Technical Data
FEATURES
ADM8845 drives 6 white LEDs from a 2.6V to 5.5V (li-ion) input supply 1x/1.5x/2x Fractional Charge Pump to maximize power efficiency 1% LED Current Matching Power Sub and main Display LEDs Low Power Shutdown Mode Package footprint only 9mm2 (3mm x 3mm) Package height only 0.9mm Shutdown Function Soft-start limiting inrush current
EVAL-ADM8845
The ADM8845 provides two digital input control pins, CTRL1 and CTRL2, which control the operation and the brightness of the LEDs. The ADM8845 is configured with a sub and main display, the main display refers to 4 of the 6 LEDs (FB1 - FB4) and the sub display refers to the remaining 2 LEDs (FB5 FB6). The ADM8845 provides the option to control the brightness of the LEDs with a digital PWM signal. The duty cycle of the PWM signal determines the brightness of the backlight LEDs. Brightness control of the LEDs can also be controlled by a DC voltage. The ADM8845 has soft-start circuitry to limit inrush current flow at power up. The ADM8845 is fabricated using CMOS technology for minimal power consumption. The part is packaged in a 16-lead LFCSP (Lead Frame Chip Scale Package).
APPLICATIONS
White LED Backlighting Micro TFT Color displays Mobile Phones with Main and Sub Displays DSC PDAs
INTRODUCTION
The ADM8845 Evaluation Board allows the ADM8845 Charge Pump Driver for LCD white LED backlights to be quickly and easily evaluated. The evaluation board allows all of the input and output functions to be exercised without the need for external components.
EVALUATION SYSTEM PACKAGE CONTENTS
The evaluation system contains the following items: ADM8845 Evaluation Board PC Parallel to Serial Cable CD containing evaluation board software
EVALUATION BOARD HARDWARE ADM8845 GENERAL DESCRIPTION
The following gives a brief description of the ADM8845 and the evaluation board hardware overview. Further information can be found in the data sheet for the device. The ADM8845 provides the power required to drive up to 6 white LEDs, using charge pump technology. The LEDs are used for backlighting a color LCD display. To maximize power efficiency, a charge pump that can operate in either a 1x, 1.5x or 2x mode is used. The charge pump automatically switches between 1x/1.5x/2x modes based on the input voltage, to maintain correct output levels at a high power efficiency. Improved brightness matching of the LEDs is achieved by the use of a feedback pin to sense individual LED current with a maximum ILED to ILED matching accuracy of 1% and ILED to ISET maximum matching of 1%.
Rev. PrB
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective companies.
The ADM8845 evaluation board contains the following main components, which can be identified from the block diagram, the schematic diagram and the printed circuit board silkscreen of figures 1,3 and 4 overleaf. 13 jumper points to facilitate the connection of external inputs and internal circuitry. 21 test points for signal connection and measurement A patchwork area to facilitate the connection up the ADM8845 Eval Board to external components.
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