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LT1947

1947fa

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TFT-LCD Notebook Display Panels

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TFT-LCD Desktop Monitor Display Panels

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Digital Cameras

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Handheld Computers

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Complete Solution Under 1.2mm

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Develops Three Outputs from a 3.3V or 5V Supply

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Externally Programmable V

Delay

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Fixed Frequency Low Noise Outputs

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All Ceramic Capacitors

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3MHz Switching Frequency

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Fast Transient Response

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Few External Components Required

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2.7V to 8V Input Range

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Adjustable AV

and V

Voltages

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Tiny 10-Lead MSOP and Thermally Enhanced

10-Lead MSOP Packages

Adjustable Output TFT-LCD

Triple Switching Regulator

Figure 1. 3.3V Powered TFT-LCD Bias Generator

The LT

1947 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. The second regulator’s output is also adjustable up

to 30V and can deliver 10mA for positive bias. A simple

level-shift charge pump off the main switch node gener-

ates the negative bias voltage. An external capacitor sets

the delay time from AV

’s final value to the rising edge at

the V

pin. The 3MHz switching frequency allows the use

of tiny low profile chip inductors and capacitors through-

out, providing a low noise, low cost total solution with all

components under 1.2mm in height. The device operates

from an input range of 2.7V to 8V and is available in

10-lead MSOP and thermally enhanced 10-lead MSOP

packages.

SW2

SW1

3.3µH

4.7µH

D3 D4

SHDN

LT1947

GND

182k

53.6k

3.3µF

CERAMIC

×2

C1: TAIYO YUDEN LMK316BJ225MD

C2: TAIYO YUDEN LMK325BJ335MD × 2

C3: AVX 0.22µF 25V X7R

C4, C6: TAIYO YUDEN LMK107BJ684MA

0.68µF

CERAMIC

0.68µF

200mA

24V

10mA

OFF

–8V

10mA

10k

1947 F01

10k

FB1

10nF

220nF

2.2µF

CERAMIC

SHUTDOWN

FB2

D1: MBRM120LT3

D2: CMDSH-3

D3, D4: BAT54S DUAL DIODE

L1: SUMIDA CLQ4D103R3

L2: TAIYO YUDEN LB2012B4R7M

2ms/DIV 1947 TA01.tif

SHDN

5V/DIV

20V/DIV

10V/DIV

OFF

10V/DIV

Start-Up Waveforms

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

, LTC and LT are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

Summary of content (12 pages)

PAGE 1
LT1947 Adjustable Output TFT-LCD Triple Switching Regulator U FEATURES DESCRIPTIO ■ The LT®1947 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. The second regulator’s output is also adjustable up to 30V and can deliver 10mA for positive bias.
PAGE 2
LT1947 W W W AXI U U ABSOLUTE RATI GS (Note 1) VIN Voltage ................................................................ 8V CT Voltage.................................................................. 6V SW1, SW2 Voltage .................................................. 36V VON, VO2 Voltage ..................................................... 30V FB1, FB2 .................................................................... 3V SHDN................................................................
PAGE 3
LT1947 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V, VSHDN = 3.3V unless otherwise specified. SYMBOL CONDITIONS Error Amplifier Voltage Gain EA1 and EA2 CT Current Source VFB1 = 1.3V MIN TYP MAX UNITS 100 V/V µA 4 5.5 6.5 CT Threshold to Turn On Q3 1.25 1.28 1.30 V FB1 Voltage to Begin CT Charge 1.17 1.2 1.23 V 1.4 2 A SW1 Current Limit (Note 3) 1.
PAGE 4
LT1947 U W TYPICAL PERFOR A CE CHARACTERISTICS SW2 Current Limit 1.0 1.6 0.8 SW2 CURRENT (A) SW1 CURRENT (A) SW1 Current Limit 1.8 1.4 1.2 1.0 0.6 0.4 0.2 0.8 –50 –25 0 25 50 TEMPERATURE (°C) 75 0 –50 100 –25 0 25 50 TEMPERATURE (°C) 75 1947 G04 1947 G05 Switch 2 Saturation Voltage Switch 1 Saturation Voltage 800 SWITCH 2 SATURATION VOLTAGE (mV) SWITCH 1 SATURATION VOLTAGE (mV) 500 400 25°C 300 90°C 200 –45°C 100 0 25°C 600 90°C 400 –45°C 200 0 0 0.2 0.4 0.6 0.
PAGE 5
LT1947 U U U PI FU CTIO S FB1 (Pin 1): Feedback Pin for First Switcher. Connect resistor divider tap here. Set AV DD according to: AVDD = 1.26V(1 + R1/R2). FB2 (Pin 2): Feedback Pin for Second Switcher. Connect resistor divider 2 here and set V ON using: VON = 1.26V (1 + R3/R4) – 160mV. VIN (Pin 6): Input Supply Pin. Must be bypassed with a ceramic capacitor close to the pin. SW2 (Pin 7): VO2 Switch Node. Connect L2 and D2 here. Minimize trace area at this pin to keep EMI down.
PAGE 6
LT1947 W BLOCK DIAGRA VIN GND SHDN VIN 5.5µA – 28mV +– R Q1 REF + – REF Q3 ∑ REF VO2 + 0.01Ω + SLOPE 1 OSC – FB2 – OSC SLOPE 1 SLOPE 2 1.26V REFERENCE AND UNDERVOLTAGE LOCKOUT SW2 S + 3MHz OSCILLATOR Q + Q4 + SW1 S + – VON OSC – FB1 CT SHUTDOWN R Q Q2 + REF REF ∑ + 0.
PAGE 7
LT1947 U OPERATIO To best understand operation of the LT1947, please refer to the LT1947 Block Diagram. The device contains two switching regulators, a timer and a high side switch. Three outputs can be generated: an adjustable AVDD output, a charge-pumped inversion of the AVDD output called VOFF, and a time delayed adjustable output called VON. Q3 keeps VON off for an externally set time interval, set by a capacitor connected to the CT pin. C = (5.5µA • tDELAY)/1.
PAGE 8
LT1947 U OPERATIO D3 D4 VOFF –8V 10mA C4 0.68µF CERAMIC AVDD 8V 200mA C6 0.68µF L1 3.3µH VIN D1 L2 4.7µH VIN SW1 SW2 C1 2.2µF CERAMIC VSS FB1 D2 VO2 C3 220nF RSS 33.2k R1 53.6k R2 10k LT1947 R3 182k FB2 R4 10k SHDN CT C2 3.3µF CERAMIC ×2 VON 24V 10mA VON GND C5 10nF CSS 33nF VOFF 1947 F03 C1: TAIYO YUDEN LMK316BJ225MD C2: TAIYO YUDEN LMK325BJ335MD ×2 C3: AVX 0.
PAGE 9
LT1947 U TYPICAL APPLICATIO S TFT-LCD Bias Generator: 12V, 20V, – 6V Output 34k Q1 BAT54S D3 C6 R1 86.6k SW1 VIN SW2 C1 4.7µF AVDD 12V 120mA D1 L2 4.7µH 34k C4 L1 4.7µH VIN 3.3V Q2 D4 C2 3.3µF CERAMIC ×2 FB1 D2 VO2 C3 0.22µF R2 10k LT1947 R3 147k FB2 R4 10k SHUTDOWN VON 20V 10mA VON GND SHDN CT VOFF –6V 20mA C5 10nF C1: TAIYO YUDEN JMK316BJ475MD 4.7µF 6.3V X7R C2: TAIYO YUDEN LMK325BJ335MD 3.3µF 10V X7R ×2 C3: AVX 0.22µF 25V X7R C4, C6: TAIYO YUDEN LMK107BJ684MA 0.
PAGE 10
LT1947 U PACKAGE DESCRIPTIO MS Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 10 9 8 7 6 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0.497 ± 0.076 (.0196 ± .003) REF 0° – 6° TYP GAUGE PLANE 1 2 3 4 5 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 1.10 (.
PAGE 11
LT1947 U PACKAGE DESCRIPTIO MSE Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1663) BOTTOM VIEW OF EXPOSED PAD OPTION 2.794 ± 0.102 (.110 ± .004) 5.23 (.206) MIN 0.889 ± 0.127 (.035 ± .005) 1 2.06 ± 0.102 (.081 ± .004) 1.83 ± 0.102 (.072 ± .004) 2.083 ± 0.102 3.20 – 3.45 (.082 ± .004) (.126 – .136) 10 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) 0.
PAGE 12
LT1947 U TYPICAL APPLICATIO TFT-LCD Bias Generator: 7.5V, 15V, – 10V Output C7 0.68µF C6 0.68µF D7 C8 D3 D5 D4 BAT54S C4 0.68µF D6 34k Q1 34k VOFF –10V 20mA L1 3.3µH VIN 3.3V D1 L2 4.7µH C1 1µF CERAMIC ×2 SW2 R1 49.9k FB1 D2 VO2 BAT54S C3 0.68µF SHUTDOWN SW1 VIN AVDD 7.5V 200mA R2 10k LT1947 R3 105k FB2 R4 10k SHDN CT C2 3.3µF CERAMIC ×2 VON GND VON 15V 10mA C5 10nF C1: TAIYO YUDEN JMK107BJ105MA 1µF 6.3V X7R ×2 C2: TAIYO YUDEN LMK325BJ335MD 3.