LT1943
High Current Quad Output
Regulator for TFT LCD Panels
FEATURES
■ 4 Integrated Switches: 2.4A Buck, 2.6A Boost,
0.35A Boost, 0.35A Inverter (Guaranteed Minimum
Current Limit)
■ Fixed Frequency, Low Noise Outputs
■ Soft-Start for all Outputs
■ Externally Programmable VON Delay
■ Integrated Schottky Diode for VON Output
■ PGOOD Pin for AVDD Output Disconnect
■ 4.5V to 22V Input Voltage Range
■ PanelProtectTM Circuitry Disables VON Upon Fault
■ Available in Thermally Enhanced 28-Lead TSSOP
U
APPLICATIO S
■ Large TFT-LCD Desktop Monitors
■ Flat Panel Televisions
, LTC and LT are registered trademarks of Linear Technology Corporation.
PanelProtect is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
DESCRIPTIO
The LT®1943 quad output adjustable switching regulator
provides power for large TFT LCD panels. The device,
housed in a low profile 28 pin thermally enhanced TSSOP
package, can generate a 3.3V or 5V logic supply along with
the triple output supply required for the TFT LCD panel.
Operating from an input range of 4.5V to 22V, a step-down
regulator provides a low voltage output VLOGIC with up to
2A current. A high-power step-up converter, a lower-
power step-up converter and an inverting converter pro-
vide the three independent output voltages AVDD, VON and
VOFF required by the LCD panel. A high-side PNP provides
delayed turn-on of the VON signal and can handle up to
30mA. Protection circuitry ensures that VON is disabled if
any of the four outputs are more than 10% below the
programmed voltage.
All switchers are synchronized to an internal 1.2MHz
clock, allowing the use of low profile inductors and ce-
ramic capacitors throughout. A current mode architecture
provides excellent transient response. For best flexibility,
all outputs are adjustable. Soft-start is included in all four
channels. A PGOOD pin can drive an optional PMOS pass
device to provide output disconnect for the AVDD output.
TYPICAL APPLICATIO
VOFF
–5.5V
50mA
VIN, 8V TO 20V
2.2µF 44.2k
0.47µF
10µF
10µH
33µH
VLOGIC
3.3V
2A
10.0k
16.2k
10.0k
22µF
SW4
NFB4
10pF 10µH
0.22µF
4.7µH
FB4
BIAS
BOOST
SW1
FB1
VC1
VIN SW3 SW2
FB2
RUN-SS
LT1943
SS-234
CT
PGOOD
VON
E3
FB3
GND
SGND
VC2 VC3
VC4
1µF
10µH
88.7k
10.0k
0.015µF
0.015µF
0.047µF
PGOOD
274k
10.0k
2.2µF
18k
100pF
2.2nF
100pF
2.2nF
6.8k 27k
100pF
680pF
13k
100pF
2.2nF
AVDD
12.2V
500mA
10µF
VON
35V
30mA
0.47µF
Quad Output TFT-LCD Power Supply
1943 TA01
RUN-SS
2V/DIV
VLOGIC
5V/DIV
AVDD
10V/DIV
VOFF
10V/DIV
VE3
20V/DIV
VON
50V/DIV
IIN(AVG)
1A/DIV
Startup Waveforms
5ms/DIV
1943fa
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