LT1942

1

1942fb

The LT

lator designed to provide all necessary power supply

functions for TFT displays, including the white LED

backlight driver. The TFT supply incorporates two boost

and one inverting DC/DC converters. The TFT supply

output voltages are independently set, unlike charge

pump solutions which have many limitations. Power

sequencing for the TFT supply is built into the part and is

user programmable.

The LED driver is a boost DC/DC converter that can be

independently controlled. The LED driver has built-in

dimming control for precise control of LED current. An 8:1

dimming range is achieved by adjusting the CTRL4 volt-

age. The user can elect to drive a single string or two

strings of LEDs. An LED ballast circuit is included to

precisely match the LED currents if two strings of LEDs are

used. Soft-start is built into the LED driver as well as the

primary TFT supply.

The LT1942 is available in a low profile (0.75mm) 24-lead

QFN (4mm

× 4mm) package.

Power Sequencing

Matching in White LEDs

(Not Charge Pump Derived)

× 4mm)

Quad DC/DC Converter

for Triple Output TFT Supply

Plus LED Driver

CTRL4

SGND/

AGND

D3

SW3

LT1942

SW1

FB1

PGND14

PGOOD

SW4

D4

LED1

LED2

FB4

FB3

PGND23

NFB2

D2

SW2

0.1

µF

0.22

µF

47

µH

47

µH

SHDN

SS1

SS4

CT

22

µH

22

µH

CMDSH-3

Si2301BDS

33

µH

301k

1M

100k

4.7pF

0.1

µF

0.1

µF

0.1

µF

1942 TA01

0.22

µF

2.2

µF

SHUTDOWN

LED CONTROL

5V

40mA

4.7

µF

4.7

µF

698k

100k

10k

3V TO 4.2V

10V

2mA

–10V

2mA

665k

4.99

Ω

20mA

20mA

TFT Bias and White LED Backlight Power Supply

APPLICATIO S

DESCRIPTIO

FEATURES

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

All other trademarks are the property of their respective owners.

TYPICAL APPLICATIO