LT1942
Quad DC/DC Converter
for Triple Output TFT Supply
Plus LED Driver
FEATURES
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DESCRIPTIO
Triple Output TFT Supply with Built-In
Power Sequencing
Integrated White LED Backlight Driver
Integrated Schottky Diodes
Active Ballast Circuitry Ensures Precise Current
Matching in White LEDs
Low Noise 1MHz Fixed Frequency Operation
2.6V to 16V Input Voltage Range
Soft-Start Limits Inrush Current
TFT Supply Output Voltages Independently Set
(Not Charge Pump Derived)
Power Good and Output Disconnect for TFT Supply
Built-In LED Dimming Capability
Open LED Protection for LED Driver
24-Lead QFN Package (4mm
×
4mm)
The LT
®
1942 is a highly integrated quad switching regu-
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
voltage.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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
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Poly-Silicon TFT Displays
Amorphous Silicon TFT Displays
TFT Bias and White LED Backlight Power Supply
V
IN
3V TO 4.2V
0.22µF
698k
V
ON
10V
2mA
10k
0.22µF
V
OFF
–10V
2mA
665k
47µH
47µH
0.1µF
0.22µF
100k
PGND23
V
OUT3
NFB2
D2
SW2
SHDN SGND/
CTRL4 AGND
SS1
SS4
0.1µF
0.1µF
LT1942
D3
FB3
SW3
22µH
22µH
V
CC
SW1
FB1
PGND14
PGOOD
SW4
D4
LED1
LED2
FB4
CT
0.1µF
4.99Ω
1942 TA01
CMDSH-3
301k
4.7pF
4.7µF
100k
33µH
V
IN
V
IN
SHUTDOWN
LED CONTROL
U
Si2301BDS
1M
AV
DD
5V
40mA
4.7µF
20mA
20mA
1942fa
U
1
LINER [ LINEAR TECHNOLOGY ]
