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LT3461/LT3461A

3461af

TYPICAL APPLICATIO

FEATURES

DESCRIPTIO

APPLICATIO S

■

Digital Cameras

■

CCD Bias Supply

■

XDSL Power Supply

■

TFT-LCD Bias Supply

■

Local 5V or 12V Supply

■

Medical Diagnostic Equipment

■

Battery Backup

5V to 12V, 70mA Step-Up DC/DC Converter

Efficiency

10µH

261k

30.1k

1µF

15pF

1µF

OUT

12V

70mA

OUT

SHDN

GND

LT3461A

3461 TA01a

OFF ON

■

Integrated Schottky Rectifier

■

Fixed Frequency 1.3MHz/3MHz Operation

■

High Output Voltage: Up to 38V

■

Low V

CESAT

Switch: 260mV at 250mA

■

12V at 70mA from 5V Input

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5V at 115mA from 3.3V Input

■

Wide Input Range: 2.5V to 16V

■

Uses Small Surface Mount Components

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Low Shutdown Current: <1µA

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Soft-Start

■

Low Profile (1mm) SOT-23 (ThinSOT

) Package

1.3MHz/3MHz Step-Up

DC/DC Converters with

Integrated Schottky in ThinSOT

The LT

3461/LT3461A are general purpose fixed fre-

quency current mode step-up DC/DC converters. Both

devices feature an integrated Schottky and a low V

CESAT

switch allowing a small converter footprint and lower parts

cost. The LT3461 switches at 1.3MHz while the LT3461A

switches at 3MHz. These high switching frequencies en-

able the use of tiny, low cost and low height capacitors and

inductors. The constant switching frequency results in

predictable output noise that is easy to filter, and the

inductor based topology ensures an input free from switch-

ing noise typically present with charge pump solutions.

The high voltage switch in the LT3461/LT3461A is rated at

40V making the device ideal for boost converters up to

38V.

The LT3461/LT3461A are available in a low profile (1mm)

SOT-23 package.

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

ThinSOT is a trademark of Linear Technology Corporation.

LOAD CURRENT (mA)

EFFICIENCY (%)

3461 TAO1b

= 5V

= 3.3V

Summary of content (8 pages)

PAGE 1
LT3461/LT3461A 1.3MHz/3MHz Step-Up DC/DC Converters with Integrated Schottky in ThinSOT U FEATURES DESCRIPTIO ■ The LT®3461/LT3461A are general purpose fixed frequency current mode step-up DC/DC converters. Both devices feature an integrated Schottky and a low VCESAT switch allowing a small converter footprint and lower parts cost. The LT3461 switches at 1.3MHz while the LT3461A switches at 3MHz. These high switching frequencies enable the use of tiny, low cost and low height capacitors and inductors.
PAGE 2
LT3461/LT3461A U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) Input Voltage (VIN) .................................................. 16V VOUT, SW Voltage .................................................... 40V FB Voltage ................................................................. 5V SHDN Voltage .......................................................... 16V Operating Ambient Temperature Range (Note 2) .................. – 40°C to 85°C Maximum Junction Temperature ......
PAGE 3
LT3461/LT3461A U W TYPICAL PERFOR A CE CHARACTERISTICS Oscillator Frequency (LT3461) Current Limit 1.6 FB Pin Voltage 1.28 480 TA = 25°C 1.27 1.4 1.3 1.2 360 FB VOLTAGE (V) CURRENT LIMIT (mA) FREQUENCY (MHz) 1.5 240 1.26 1.25 1.24 120 1.1 1.23 1.0 –40 –20 40 20 60 0 TEMPERATURE (°C) 80 0 10 100 20 30 40 50 60 70 DUTY CYCLE (%) 80 3461a G01 1.22 –40 –20 90 480 320 TA = 25°C 3.0 2.7 2.4 280 SHDN PIN CURRENT (µA) CURRENT LIMIT (mA) FREQUENCY (MHz) TA = 25°C 420 3.
PAGE 4
LT3461/LT3461A U U U PI FU CTIO S SW (Pin 1): Switch Pin. Connect inductor here. Minimize trace at this pin to reduce EMI. SHDN (Pin 4): Shutdown Pin. Tie to 1.5V or higher to enable device; 0.4V or less to disable device. Also functions as soft-start. Use RC filter (47k, 47nF typ) as shown in Figure 1. GND (Pin 2): Ground Pin. Tie directly to local ground plane. VOUT (Pin 5): Output Pin. Connect to resistor divider. Put capacitor close to pin and close to GND plane. FB (Pin 3): Feedback Pin.
PAGE 5
LT3461/LT3461A U W U U APPLICATIO S I FOR ATIO The LT3461 has a built-in Schottky diode. When supply voltage is applied to the VIN pin, the voltage difference between VIN and VOUT generates inrush current flowing from input through the inductor and the Schottky diode to charge the output capacitor. The maximum nonrepetitive surge current the Schottky diode in the LT3461 can sustain is 1.5A. The selection of inductor and capacitor value should ensure the peak of the inrush current to be below 1.5A.
PAGE 6
LT3461/LT3461A U W U U APPLICATIO S I FOR ATIO Inductor Selection The inductors used with the LT3461/LT3461A should have a saturation current rating of 0.3A or greater. If the device is used in an application where the input supply will be hot-plugged, then the saturation current rating should be equal to or greater than the peak inrush current. For the LT3461, an inductor value between 10µH and 47µH, depending upon output voltage, will usually be the best choice for most designs.
PAGE 7
LT3461/LT3461A U TYPICAL APPLICATIO S 3.3V to 5V Step-Up Converter Efficiency 80 3.3V to 5V Step-Up Converter (LT3461A) L1 4.7µH VIN 3.3V C1 1µF OFF ON R1 45.3k EFFICIENCY (%) 75 1 SW 6 5 VIN VOUT LT3461A 4 3 SHDN FB GND 2 VOUT 5V 115mA 15pF C2 1µF R2 15k C1, C2: TAIYO YUDEN X7R LMK212BJ105 L1: MURATA LQH32CN4R7M33 OR EQUIVALENT 70 65 3461a TA03a 60 0 30 60 90 LOAD CURRENT (mA) 120 3461a TA03b U PACKAGE DESCRIPTIO S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.
PAGE 8
LT3461/LT3461A U TYPICAL APPLICATIO S Low Profile (1mm) 3.3V to 15V Step-Up Converter 3.3V to 15V Efficiency L1 10µH C1 1µF OFF ON 1 SW 5 VIN VOUT LT3461A 4 3 SHDN FB GND 2 70 VOUT 15V 25mA 6 332k EFFICIENCY (%) VIN 3.3V 75 22pF C2 2.2µF 30.