Charge Pump Driver for LCD
GENERAL DESCRIPTION
The ADM8845 uses charge pump technology to provide the power required to drive up to six LEDs. The LEDs are used for backlighting a color LCD display, having regulated constant current for uniform brightness intensity. The main display can have up to four LEDs, and the sub display can have one or two LEDs. The digital CTRL1 and CTRL2 input control pins control the shutdown operation and the brightness of the main and sub displays.
To maximize power efficiency, the charge pump can operate in a 1×, 1.5×, or 2× mode. The charge pump automatically
switches between 1×/1.5×/2× modes, based on the input voltage, to maintain sufficient drive for the LED anodes at the highest power efficiency.
Improved brightness matching of the LEDs is achieved by a feedback pin to sense individual LED current with a maximum matching accuracy of 1%.
FEATURES
Drives 6 LEDs from 2.6 V to 5.5 V (Li-Ion) input supply 1×/1.5×/2× fractional charge pump to maximize power efficiency
1% max LED current matching
Up to 88% power efficiency over Li-Ion range
Powers main and sub display LEDs with individual shutdown Package footprint only 9 mm2 (3 mm × 3 mm) Package height only 0.9 mm Low power shutdown mode Shutdown function
Soft-start limiting in-rush current
APPLICATIONS
Cellular phones with main and sub displays White LED backlighting
Camera flash/strobes and movie lights Micro TFT color displays DSC PDAs
C1C2FUNCTIONAL BLOCK DIAGRAM
4.7µR
Figure 1.
Rev. C
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 owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 http://www.77cn.com.cn Fax: 781.461.3113© 2004–2011 Analog Devices, Inc. All rights reserved.