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LTC3524

Adjustable TFT Bias Supply with WLED Driver

Linear Technology 

FEATURES

■ Generates Three Adjustable, Low Noise Rails for

Small/Medium TFT Displays

■ Drives Up to Ten White LEDs

■ LED Dimming and Open-Circuit Protection

■ Controlled Power-Up/Power-Down Sequencing

■ 1.5MHz Fixed Frequency, Low Noise Operation

■ VIN Range 2.5V to 6V, VOUT Range 3V to 6V

■ TFT Supply Efficiency Up to 90%

■ LED Supply Efficiency Up to 78%

■ Two Independantly Enabled LED Strings

■ 200 to 1 True Color PWMTM Dimming

■ Tiny External Solution

■ 24-Lead QFN Package (4mm × 4mm × 0.75mm)

APPLICATIONS

■ PDAs, Palmtop Computers

■ Digital Still and Video Cameras

■ Handheld GPS

■ Portable Instrument Displays

■ Portable Media Players

LTC3524

Adjustable TFT Bias Supply

with WLED Driver

DESCRIPTION

The LTC®3524 is an integrated BIAS and white LED power

converter solution for small/medium-sized polysilicon thin

film transistor (TFT) liquid crystal (LCD) display panels.

The device operates from a single Lithium-Ion/polymer

battery or any voltage source between 2.5V and 6V.

A 1.5MHz synchronous boost converter generates a pro-

grammable low noise, high efficiency 25mA TFT supply

of up to 6.0V. Regulated, low ripple charge pumps are

used to generate up to +20V and –20V at 2mA. Output

sequencing is internally controlled to insure proper

initialization and rapid discharge of the LCD panel in

shutdown.

A second 1.5MHz boost converter powers one or two LED

strings with up to five series elements each. LED current

and display brightness can be controlled over a wide range

using analog or digital means up to 25mA.

The LTC3524 is offered in the 4mm × 4mm 24-pin QFN

package, minimizing the total solution footprint.

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

True Color PWM is a registered trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners.

TYPICAL APPLICATION

+5V, –7.5V, +12.5V, 8 LED Power Supply

+

–

+5V

25mA

+12.5V

2mA

Li-Ion

2.2μF

10μH 3.3μH

SW1

VIN

SW2

VLED

10μF 324k

+10V

0.47μF

0.47μF 220k

VOUT

1M

LED2

0.1μF

FBVO

VNIN

V2x

C2+

C2–

VH

LTC3524

LED1

PROG

ELED2

ELED1

ELCD

FBN

2M

FBH

VN

CH+ CH– GND CN+

0.1μF

0.1μF

10μF

100k for 20mA

470k

1M

VIN

VOUT

–7.5V

2mA

0.47μF

3524 TA01a

LCD Bias and LED Efficiency

VIN = 3.6V, VOUT = 5V, 8 LEDs

100

VIN = 3.6V

90

LCD

80

LED

70

60

5

10

15

20

25

VOUT OR LED STRING CURRENT (mA)

3524 TA01b

3524f

1

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