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LT1948 Datasheet Preview

LT1948 Datasheet

DC/DC Converter

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NOT RECOMMENDED FOR NEW DESIGNS
Contact Linear Technology for Potential Replacement
FEATURES
s Complete Solution Under 1.2mm
s Develops Three Outputs from a 3.3V or 5V Supply
s Externally Programmable VON Delay
s Fixed Frequency Low Noise Outputs
s All Ceramic Capacitors
s Operates at 3MHz Switching Frequency
s Fast Transient Response
s Few External Components Required
s 2.6V to 6V Input Range
s Tiny 8-Lead MSOP Package
U
APPLICATIO S
s TFT-LCD Notebook Display Panels
s TFT-LCD Desktop Monitor Display Panels
s Digital Cameras
s Handheld Computers
Final Electrical Specifications
LT1948
DC/DC Converter for
TFT-LCD Panels
August 2000
DESCRIPTIO
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
AVDD reaching final value to 23V appearing at the VON 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
VIN
2.5V TO
6V
C1
2.2µF
L3
2.2µH
D2
CMDSH-3
C3
0.22µF
L1, 2.2µH
L2, 2.2µH
C4
0.22µF
D1
MBRM120
C5
1µF
VIN
SW2
LT1948
VO2
CT
C6
22nF
SW1
FB1
VON
GND
R1
53.6k
R2
10k
C1, C2: TAIYO YUDEN LMK212BJ225
C3: TAIYO YUDEN TMK316BJ224
C4: TAIYO YUDEN EMK212BJ224
C5: TAIYO YUDEN LMK212BJ105
L1–L3: TAIYO YUDEN LB2012-2R2
VOFF
–8V
15mA
AVDD
8V
260mA
C2
2.2µF
VON
23V
10mA
1948 F01
Figure 1. 3.3V Powered TFT-LCD Bias Generator
VIN
5V/DIV
VON
20V/DIV
AVDD
10V/DIV
VOFF
10V/DIV
Start-Up Waveforms
2ms/DIV
1948 TA01a
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.
1




LINEAR

LT1948 Datasheet Preview

LT1948 Datasheet

DC/DC Converter

No Preview Available !

LT1948
ABSOLUTE AXI U RATI GS
(Note 1)
VIN Voltage ................................................................ 8V
CT Voltage.................................................................. 6V
SW1, SW2 Voltage .................................................. 36V
FB Voltage ................................................................. 3V
VON, VO2 Voltage..................................................... 30V
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Lead Temperature (Soldering, 10 sec).................. 300°C
UW U
PACKAGE/ORDER I FOR ATIO
TOP VIEW
FB1 1
CT 2
SW1 3
GND 4
8 VON
7 VO2
6 SW2
5 VIN
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 200°C/W
ORDER PART
NUMBER
LT1948EMS8
MS8 PART
MARKING
LTNR
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS The q denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V unless otherwise specified.
SYMBOL
Supply Current
Reference Voltage
Reference Line Reg
CT Source Current
CT Voltage to Turn On Q3
FB1 Voltage to Begin CT Charge
SW1 Current Limit
SW2 Current Limit
SW1 Saturation Voltage
SW2 Saturation Voltage
Oscillator Frequency
Maximum Duty Cycle
VO2 Pin Resistance
SW1, SW2 Error Amp Gain
SW1, SW2 Error Amp Gm
FB1 Regulation Voltage
FB1 Line Regulation
VO2 Regulation Voltage
VON Switch Drop
SW1 Leakage Current
SW2 Leakage Current
CONDITIONS
Not Switching
2.7V < VIN < 8V
VFB1 = 1.3V
(Note 3)
(Note 3)
ISW1 = 800mA
ISW2 = 300mA
0°C TA 85°C
–40°C TA 0°C
Measured to Ground
2.7V < VIN < 8V
VO2 = 25V, 7mA Load from VON, CT Voltage >1.30V
Switch Off, SW1 Voltage = 3.3V
Switch Off, SW2 Voltage = 3.3V
MIN
4.5
1.25
1.17
1.2
0.5
q 2.4
70
q 69
q 67
1.240
q 1.230
22
TYP
7
1.26
0.01
5.5
1.28
1.20
1.5
0.8
350
250
3.2
75
400
100
50
1.260
0.01
23
200
0.01
0.01
MAX
13
6.5
1.30
1.23
410
300
3.6
90
1.280
1.285
0.05
24
260
5
2
UNITS
mA
V
%/V
µA
V
V
A
A
mV
mV
MHz
%
%
%
k
V/V
µA/V
V
V
V
mV
µA
µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1948 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the – 40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Current limit guaranteed by design and/or correlation to static test.
2


Part Number LT1948
Description DC/DC Converter
Maker LINEAR
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LT1948 Datasheet PDF






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