LT1948 DC/DC Converter TFT-LCD Panels August 2000 FEATURES

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LT1948 DC/DC Converter TFT-LCD Panels August 2000 FEATURES

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LT1948 DC/DC Converter TFT-LCD Panels
August 2000
FEATURES
DESCRIPTIO
Complete Solution Under 1.2mm Develops Three Outputs from 3.3V Supply Externally Programmable Delay Fixed Frequency Noise Outputs Ceramic Capacitors Operates 3MHz Switching Frequency Fast Transient Response External Components Required 2.6V Input Range Tiny 8-Lead MSOP Package
APPLICATIO
TFT-LCD Notebook Display Panels TFT-LCD Desktop Monitor Display Panels Digital Cameras Handheld Computers
LT®1948 highly integrated multiple output DC/DC converter designed TFT-LCD panels. device contains independent switching regulators: main regulator adjustable output voltage with internal 1.1A switch that generate boosted voltage high while second regulator generates 10mA positive bias. simple level-shift charge pump main switch node generates negative bias voltage. external capacitor sets delay time from AVDD reaching final value appearing pin. 3MHz switching frequency allows tiny profile chip inductors capacitors throughout, providing noise, cost total solution with components under 1.25mm height. device operates from input range 2.6V available 8-lead MSOP package.
registered trademarks Linear Technology Corporation.
TYPICAL APPLICATIO
BAT54S
VOFF 15mA
2.2µH 2.5V 2.2µF 2.2µH LT1948 0.22µF 22nF 2.2µH
0.22µF MBRM120
AVDD 260mA 53.6k 2.2µF 10mA
5V/DIV 20V/DIV
CMDSH-3
AVDD 10V/DIV
VOFF 10V/DIV TAIYO YUDEN LMK212BJ105 L1-L3: TAIYO YUDEN LB2012-2R2 2ms/DIV
1948
TAIYO YUDEN LMK212BJ225 TAIYO YUDEN TMK316BJ224 TAIYO YUDEN EMK212BJ224
Figure 3.3V Powered TFT-LCD Bias Generator
Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
Start-Up Waveforms
1948 TA01a
LT1948
ABSOLUTE
(Note
RATI
PACKAGE/ORDER ATIO
VIEW
Voltage Voltage. SW1, Voltage Voltage VON, Voltage. Operating Temperature Range (Note 40°C 85°C Lead Temperature (Soldering, sec). 300°C
ORDER PART NUMBER LT1948EMS8 PART MARKING LTNR
PACKAGE 8-LEAD PLASTIC MSOP TJMAX 125°C, 200°C/W
Consult factory Industrial Military grade parts.
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. 3.3V unless otherwise specified.
SYMBOL Supply Current Reference Voltage Reference Line Source Current Voltage Turn Voltage Begin Charge Current Limit Current Limit Saturation Voltage Saturation Voltage Oscillator Frequency Maximum Duty Cycle 85°C -40°C Resistance SW1, Error Gain SW1, Error Regulation Voltage
ELECTRICAL CHARACTERISTICS
CONDITIONS Switching 2.7V VFB1 1.3V
1.26 0.01
UNITS
1.25 1.17
1.28 1.20
1.30 1.23
(Note (Note ISW1 800mA ISW2 300mA
Measured Ground
1.240 1.230 1.260 0.01 0.01 0.01 1.280 1.285 0.05
µA/V
Line Regulation Regulation Voltage Switch Drop Leakage Current Leakage Current
2.7V 25V, Load from VON, Voltage >1.30V Switch Off, Voltage 3.3V Switch Off, Voltage 3.3V
Note Absolute Maximum Ratings those values beyond which life device impaired. Note LT1948 guaranteed meet performance specifications from 70°C. Specifications over 40°C 85°C operating
temperature range assured design, characterization correlation with statistical process controls. Note Current limit guaranteed design and/or correlation static test.
LT1948
CTIO
(Pin Feedback First Switcher. Connect resistor divider here. AVDD according AVDD 1.26V(1 R1/R2). (Pin Timing Capacitor Pin. Connect 22nF capacitor from ground program delay from reaching 1.26V turning (Pin AVDD Switch Node. Connect inductor here (see Figure Minimize trace area this keep down. (Pin Ground. Connect directly local ground plane. (Pin Input Supply Pin. Must bypassed with ceramic capacitor close pin. (Pin Switch Node. Connect inductor here. Minimize trace area this keep down. (Pin Sense Output. Connect output capacitor. This node also internally connected emitter (see Block Diagram), high side switch between VON. (Pin This Delayed Output. becomes after internal timer times out.
OPERATIO
best understand operation LT1948, please refer LT1948 Block Diagram. device contains switching regulators, timer high side switch. Three outputs generated: adjustable AVDD output, charge-pumped inversion AVDD output, called VOFF, 23V/15mA output, called VON. keeps externally time interval, capacitor connected pin. switching frequency both switchers 3MHz, internally. switchers current mode internally compensated. main AVDD switcher current limited 1.5A, while second switcher limited 800mA. They share same 1.26V reference voltage.
AVDD
When input voltage below approximately 2.4V, undervoltage lockout circuit disables switching. When AVDD less than final voltage, turned holding ground. When AVDD reaches final value, lets pin, allowing 5.5µA current source charge external capacitor, When voltage reaches 1.25V, turns connecting VON. Capacitor value calculated using following formula: (5.5µA tDELAY)/1.25V 22nF capacitor results approximately delay.
L1-L2
VOFF
1948
Figure Recommended Component Placement
LT1948
BLOCK DIAGRA
0.01
SLOPE
28mV
1.26V REFERENCE UNDERVOLTAGE LOCKOUT
3MHz OSCILLATOR
SLOPE SLOPE
0.03
SLOPE
1948BD
RELATED PARTS
PART NUMBER LT1949 LT1317 LT1308B LT1615 LT1930 DESCRIPTION 600kHz, Switch DC/DC Converter 2-Cell Micropower DC/DC with Low-Battery Detect 600kHz Single Cell Step-Up Regulator Micropower Step-Up Regulator SOT-23 1.2MHz, Step-Up Regulator SOT-23 COMMENTS 175mA from 3.3V Input 3.3V 200mA from 2-Cell Input from 1-Cell Li-Ion Battery 12mA from 2.5V Input, 5-Lead SOT-23 Package 480mA from 3.3V, 5-Lead SOT-23 Package
1948i LT/TP 0800 PRINTED
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408)432-1900 FAX: (408) 434-0507 www.linear-tech.com
LINEAR TECHNOLOGY CORPORATION 2000

LT1948 DC/DC Converter TFT-LCD Panels August 2000 FEATURES

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