LT1942_15 Datasheet, PDF (1/16 Pages) Linear Technology – Quad DC/DC Converter for Triple Output TFT Supply Plus LED Driver

FEATURES
■ _{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)}
U
APPLICATIO S
■ _{Poly-Silicon TFT Displays}
■ _{Amorphous Silicon TFT Displays}
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
LT1942
Quad DC/DC Converter
for Triple Output TFT Supply
Plus LED Driver
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.
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.
TYPICAL APPLICATIO
TFT Bias and White LED Backlight Power Supply
V_IN
3V TO 4.2V
2.2µF
V_ON
0.22µF
10V
2mA
10k
0.22µF
V_OFF
–10V
2mA
665k
V_IN
SHUTDOWN
LED CONTROL
47µH
47µH
22µH ^CMDSH-3
22µH
301k 4.7pF
698k _{D3 SW3}
V_CC
SW1
FB3
FB1
100k 4.7µF
100k
PGND14
PGND23
PGOOD
V_OUT3
NFB2
LT1942
SW4
33µH
V_IN
D4
D2
0.1µF
SW2
LED1
LED2
SHDN _SGND/
CTRL4 AGND SS1
FB4
SS4 CT
0.1µF
0.1µF ^4.99Ω
0.1µF
Si2301BDS
1M
AV_DD
5V
40mA
4.7µF
20mA 20mA
1942 TA01
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