ADM8845ACPZ-REEL7;ADM8845ACPZ-REEL;ADM8845EB-EVALZ;中文规格

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

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Brightness Control with a Digital PWM Signal ..................... 11 LED Brightness Control Using a PWM Signal Applied to

VPWM ............................................................................................. 13 LED Brightness Control Using a DC Voltage Applied to

VBRIGHT .......................................................................................... 13 Applications ..................................................................................... 14 Layout Considerations and Noise ............................................ 14 White LED Shorting .................................................................. 14 Driving Fewer than Six LEDs ................................................... 14 Driving Flash LEDs .................................................................... 15 Driving Camera Light, Main, and Sub LEDs.......................... 15 Driving Four Backlight White LEDs and Flash LEDs ........... 16 Power Efficiency ......................................................................... 17 Outline Dimensions ....................................................................... 18 Ordering Guide .......................................................................... 18

TABLE OF CONTENTS

Features .............................................................................................. 1 Applications ....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 Specifications ..................................................................................... 3 Absolute Maximum Ratings ............................................................ 4 Thermal Characteristics .............................................................. 4 ESD Caution .................................................................................. 4 Pin Configuration and Function Descriptions ............................. 5 Typical Performance Characteristics ............................................. 6 Theory of Operation ...................................................................... 10 Output Current Capability ........................................................ 11 Automatic Gain Control ............................................................ 11 Current Matching ....................................................................... 11

REVISION HISTORY

1/11—Rev. B to Rev. C

Changes to Figure 18 and Figure 19 ................................................ 8 Changes to Ordering Guide ........................................................... 18 4/10—Rev. A to Rev. B

Changes to Figure 2 ........................................................................... 5 Changes to Figure 4 ........................................................................... 6 Changes to Figure 16 to Figure 19 ................................................... 8 Changes to Brightness Control with a digital PWM

Signal Section ................................................................................... 11 Added Exposed Pad Notation to Outline Dimensions .............. 18 Changes to Ordering Guide ........................................................... 18 7/05—Rev. 0 to Rev. A

Changes to Table 3 ............................................................................. 5 C …… 此处隐藏：5583字，全部文档内容请下载后查看。喜欢就下载吧 ……