Analog Devices ADM8846 pra Datasheet

Charge Pump Driver for LCD

Preliminary Technical Data

FEATURES

ADM8846 drives 6 LEDs from a 2.6 V to 5.5 V (li-ion) input supply

1x/1.5x/2x Fractional Charge Pump to maximise 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 9mm Package height only 0.9mm Low power shutdown mode Shutdown Function Soft-start limiting inrush current

APPLICATIONS

Mobile phones with Main and Sub Displays White LED Backlighting Camera Flash/Strobes and Movie Light Applications Micro TFT color displays DSC PDA’s

2

(3mm x 3mm)

FUNCTIONAL BLOCK DIAGRAM

C1 C2

White LED Backlights

ADM8846

GENERAL DESCRIPTION

The ADM8846 provides the power required to drive up to six LEDs, using charge pump technology. The LEDs are used for backlighting a color LCD display, with up to four LEDs in the main display and up to two LEDs in the sub display, with regulated constant current for uniform brightness intensity. Two digital input control pins, CTRL1 and CTRL2 control the shutdown operation and the brightness of the main and sub displays.

To maximize power efficiency, a charge pump that can operate in either of 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 sufficient drive for the LED anodes at the highest 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 matching accuracy of 1%.

VCC

Rset

C4

CTRL1 CTRL2

Iset

ADM8846

Control

Logic

LED Current Control Circuit

Charge Pump 1x/1.5x/2x mode

Osc

Vref

Current

Control

2

1

Current Controlled Sinks

Current Control

GND

3

Figure 1. ADM8846 FUNCTIONAL BLOCK DIAGRAM

Rev. PrA_06/04

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.

+

-

Current Control

Vout

C3

MAIN

FB1

FB2

FB3 FB4

FB5 FB6

Current

Control

5

4

6

SUB

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ADM8846 Preliminary Technical Data

TABLE OF CONTENTS

General Description..................................................................... 1

ADM8846—Specifications...............................................................3

Thermal Characteristics .............................................................. 3

Absolute Maximum Ratings.............................................................4

ESD Caution.................................................................................. 4

Pin Configuration and Function Description ...............................5

Typical Performance Characteristics ..............................................6

ADM8846 Operation ..................................................................... 10

Output Current Capability........................................................ 11

Automatic Gain Control............................................................ 11

Current Matching....................................................................... 11

ADM8846 Brightness Control With a Digital PWM Signal..... 12

REVISION HISTORY

REV. PrA 06/04

ADM8846 LED Brightness Control Using a PWM Signal Applied to V

ADM8846 LED Brightness Control Using a DC Voltage Applied to V

ADM8846 Applications ..................................................................15

Layout considerations and noise .............................................. 15

White LED Shorting .................................................................. 15

Driving Fewer than six LEDs.................................................... 15

Driving Flash LEDs.................................................................... 15

Driving Camera Light, Main and sub leds.............................. 16

ADM8846 Power Efficiency...........................................................17

Outline Dimensions........................................................................18

Ordering Guide .......................................................................... 18

.......................................................................... 14

PWM

....................................................................... 14

BRIGHT

Rev. PrA 06/04 | Page 2 of 18

Preliminary Technical Data ADM8846

ADM8846—SPECIFICATIONS

(VCC = +2.6V TO 5.5V; T

Table 1.

PARAMETER Min Typ Max Units Test Conditions

Input Voltage,VCC 2.6 5.5 V Supply Current,ICC 2.6 4 m A All 6 LEDs Disabled, Vcc = 3.3V, R CTRL1 = 1, CRTL2 = 1 Shutdown Current 5 uA TA= 25°C Charge-Pump Frequency 1.5 M H z Charge Pump Mode Thresholds

1.5x to 2x 3.33 V Accuracy 4 %

2x to 1.5x 3.36 V

Accuracy 4 % Hysteresis 40 m V

1x to 1.5x 4.77 V

Accuracy 4 %

1.5x to 1x 4.81 V Accuracy 4 % Hysteresis 40 m V

Iset Pin

LED : LED Matching -1 +1 % I LED : I

Accuracy -1 +1 %

SET

Iset pin voltage 1.18 V I

to I

LED

Ratio 120

SET

Min Compliance on FB pin 0.2 0.3 V I Charge Pump Output Resistance 1.2 1.7 Ohm 1x Mode

3.5 4.5 Ohm 1.5x Mode

8.0 11 Ohm 2x Mode LED Current 30 m A See Note 1 and Figure 22 PWM 0.1 200 KHz Digital Inputs Input Hi 1.6 V Input Low 0.4 V

Input Leakage Current 1 uA Charge Pump Power Efficiency 88 % CTRL1 = 1, CRTL2 = 1, Vcc = 3.4V, V I Vout Ripple 30 m V Vcc = 3.6V, I

THERMAL CHARACTERISTICS

16-Lead LFCSP Package:

θ

= 50°C/Watt

JA

= -40°C to 85°C unless otherwise noted; C1,C2 = 1.0µF; C3 = 2.2µF; C4 = 4.7µF)

A

= 20mA, VFB =0.4V

LED

= 20mA, R

I

LED

= 7.08K, VFB =0.4V, Vcc = 3.6V, TA = 25°C,

SET

Note 2

= 20mA

SET

2.6V ≤ Vcc ≤ 4.2V

= 20mA

FB

= 20mA, All 6 LEDs Enabled

LED

= 7.08kOhm

SET

= 0.2V,

FB

Rev. PrA 06/04| Page 3 of 18

ADM8846 Preliminary Technical Data

ABSOLUTE MAXIMUM RATINGS

Table 2. (TA = 25°C unless otherwise noted)

Parameter Rating

Supply Voltage VCC –0.3 V to +6.0 V I

–0.3 V to +2.0 V

SET

CTRL1, CTRL2 –0.3 V to +6.0 V V

shorted (Note 3) Indefinite

OUT

Feedback pins FB1 to FB6 –0.3 V to +6.0 V Operating Temperature Range –40°C to +85°C V

(Note 4) 180mA

OUT

Storage Temperature Range –65°C to +125°C Power Dissipation 2mW ESD Class 1

Note 1: LED Current should be derated above T

> 65C, refer to

A

Figure 22. Note 2: Guaranteed by design. Not 100% production tested. Note 3: Short through LED. Note 4: Based on long term current density limitations.

Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

ESD CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.

Main Display

Sub Display

Vcc

2.6V- 5.5V

VOUT

ADM8846

CTRL1 CTRL2

I

SET

R

SET

GND

FB1 FB2 FB3 FB4 FB5 FB6

Figure 2. ADM8846 Typical Application Diagram

Rev. PrA 06/04 | Page 4 of 18

Preliminary Technical Data ADM8846

PIN CONFIGURATION AND FUNCTION DESCRIPTION

Table 3.

ADM8846

1 VOUT

2 C2+ Flying Capacitor 2 Positive Connection

3 I

4 FB1

5 FB2

6 FB3

7 FB4

8 FB5

9 FB6

10 G N D Device Ground Pin. 11 C2− Flying Capacitor 2 Negative Connection.

12 CTRL2

13 CTRL1

14 C1− Flying Capacitor 1 Negative Connection.

15 Vcc

16 C1+ Flying Capacitor 1 Positive Connection.

- EP Expose Paddle. Connect the exposed paddle to GND.

Mnemonic Function

Charge Pump Output. A 2.2µF capacitor to ground is required on this pin. Connect Vout to the anodes of all the LEDs.

SET

Bias current set input. The current flowing through the R I

curent. Connect a resistor R

LED

LED1 Cathode connection and Charge Pump Feedback. The current flowing in LED1 is 120 times the current flowing through R

LED2 Cathode connection and Charge Pump Feedback. The current flowing in LED2 is 120 times the current flowing through R

LED3 Cathode connection and Charge Pump Feedback. The current flowing in LED3 is 120 times the current flowing through R

LED4 Cathode connection and Charge Pump Feedback. The current flowing in LED4 is 120 times the current flowing through R

LED5 Cathode connection and Charge Pump Feedback. The current flowing in LED5 is 120 times the current flowing through R

LED6 Cathode connection and Charge Pump Feedback. The current flowing in LED6 is 120 times the current flowing through R

Digital Input. 3 V CMOS Logic. Used with CTRL1 to control the shutdown operation of the main and sub LEDs.

Digital Input. 3 V CMOS Logic. Used with CTRL2 to control the shutdown operation of the main and sub LEDs.

Positive Supply Voltage Input. Connect this pin to a 2.6 V to 5.5 V supply with a 4.7µF decoupling capacitor.

resistor I

to GND to set the bias current as V

SET

, I

.

SET

, I