Final Electrical Specifications
NOT RECOMMENDED FOR NEW DESIGNS
Contact Linear Technology for Potential Replacement
LT1948
DC/DC Converter for
TFT-LCD Panels
August 2000
FEATURES
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DESCRIPTIO
Complete Solution Under 1.2mm
Develops Three Outputs from a 3.3V or 5V Supply
Externally Programmable V
ON
Delay
Fixed Frequency Low Noise Outputs
All Ceramic Capacitors
Operates at 3MHz Switching Frequency
Fast Transient Response
Few External Components Required
2.6V to 6V Input Range
Tiny 8-Lead MSOP Package
APPLICATIO S
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TFT-LCD Notebook Display Panels
TFT-LCD Desktop Monitor Display Panels
Digital Cameras
Handheld Computers
The LT
®
1948 is a highly integrated multiple output DC/DC
converter designed for use in TFT-LCD panels. The device
contains two independent switching regulators: the main
regulator has an adjustable output voltage with an internal
1.1A switch that can generate a boosted voltage as high as
30V while the second regulator generates 23V at up to
10mA for positive bias. A simple level-shift charge pump
off the main switch node generates the negative bias
voltage. An external capacitor sets the delay time from
AV
DD
reaching final value to 23V appearing at the V
ON
pin.
The 3MHz switching frequency allows the use of tiny low
profile chip inductors and capacitors throughout, provid-
ing a low noise, low cost total solution with all components
under 1.25mm in height. The device operates from an
input range of 2.6V to 6V and is available in an 8-lead
MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
D3A
BAT54S
D3B
C5
1µF
V
OFF
–8V
15mA
L1, 2.2µH
V
IN
2.5V TO
6V
C1
2.2µF
L3
2.2µH
V
IN
SW2
LT1948
VO2
C3
0.22µF
C
T
C6
22nF
L2, 2.2µH
C4
0.22µF
D1
MBRM120
AV
DD
8V
260mA
R1
53.6k
C2
2.2µF
R2
10k
V
ON
23V
10mA
V
IN
5V/DIV
V
ON
20V/DIV
SW1
FB1
D2
CMDSH-3
V
ON
GND
AV
DD
10V/DIV
V
OFF
10V/DIV
C5: TAIYO YUDEN LMK212BJ105
L1–L3: TAIYO YUDEN LB2012-2R2
2ms/DIV
1948 F01
C1, C2: TAIYO YUDEN LMK212BJ225
C3: TAIYO YUDEN TMK316BJ224
C4: TAIYO YUDEN EMK212BJ224
Figure 1. 3.3V Powered TFT-LCD Bias Generator
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
Start-Up Waveforms
1948 TA01a
U
U
1
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
