LT1942
Quad DC/DC Converter
for Triple Output TFT Supply
Plus LED Driver
U
FEATURES
DESCRIPTIO
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.
■
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
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
preciselymatchtheLEDcurrentsiftwostringsofLEDsare
used. Soft-start is built into the LED driver as well as the
primary TFT supply.
(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)
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APPLICATIO S
■
Poly-Silicon TFT Displays
Amorphous Silicon TFT Displays
■
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.
TFT Bias and White LED Backlight Power Supply
CMDSH-3
22µH
AV
5V
Si2301BDS
1M
DD
V
IN
3V TO 4.2V
22µH
40mA
0.22µF
301k
100k
4.7pF
698k
100k
D3
FB3
SW3
V
SW1
FB1
CC
V
0.22µF
4.7µF
ON
20mA
20mA
4.7µF
10V
PGND14
PGOOD
SW4
2mA
PGND23
10k
V
IN
V
OUT3
LT1942
33µH
0.22µF
NFB2
D2
D4
665k
LED1
LED2
47µH
47µH
V
–10V
2mA
OFF
0.1µF
SW2
SHDN
CTRL4 AGND SS1
FB4
SS4 CT
SGND/
V
IN
SHUTDOWN
1942 TA01
4.99Ω
0.1µF
0.1µF
0.1µF
LED CONTROL
1942fa
1