LT1074/LT1076

1

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

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

Step-Down Switching

Regulator

The LT

bipolar switching regulator which requires only a few

external parts for normal operation. The power switch, all

oscillator and control circuitry, and all current limit com-

ponents, are included on the chip. The topology is a classic

s

Buck Converter with Output Voltage Range of 2.5V

to 50V

s

Tapped-Inductor Buck Converter with 10A Output

at 5V

s

Positive-to-Negative Converter

s

Negative Boost Converter

s

Multiple Output Buck Converter

s

5A Onboard Switch (LT1074)

s

100kHz Switching Frequency

s

Greatly Improved Dynamic Behavior

s

Available in Low Cost 5 and 7-Lead Packages

s

Only 8.5mA Quiescent Current

s

Programmable Current Limit

s

Operates Up to 60V Input

s

Micropower Shutdown Mode

positive “buck” configuration but several design innova-

tions allow this device to be used as a positive-to-negative

converter, a negative boost converter, and as a flyback

converter. The switch output is specified to swing 40V

below ground, allowing the LT1074 to drive a tapped-

inductor in the buck mode with output currents up to 10A.

The LT1074 uses a true analog multiplier in the feedback

loop. This makes the device respond nearly instanta-

neously to input voltage fluctuations and makes loop gain

independent of input voltage. As a result, dynamic behav-

ior of the regulator is significantly improved over previous

designs.

On-chip pulse by pulse current limiting makes the LT1074

nearly bust-proof for output overloads or shorts. The input

voltage range as a buck converter is 8V to 60V, but a self-

boot feature allows input voltages as low as 5V in the

inverting and boost configurations.

The LT1074 is available in low cost TO-220 or TO-3

packages with frequency pre-set at 100kHz and current

limit at 6.5A (LT1076 = 2.6A). A 7-pin TO-220 package is

also available which allows current limit to be adjusted

down to zero. In addition, full micropower shutdown can

be programmed. See Application Note 44 for design

details.

A fixed 5V output, 2A version is also available. See LT1076-5.

Buck Converter Efficiency

Basic Positive Buck Converter

+

+

GND

FB

LT1074

5V

5A

C1

500

R1

2.8k

1%

R2

2.21k

1%

MBR745*

10V TO 40V

C3

†

200

R3

2.7k

C2

0.01

L1**

50

100

USE MBR340 FOR LT1076

COILTRONICS #50-2-52 (LT1074)

#100-1-52 (LT1076)

PULSE ENGINEERING, INC.

#PE-92114 (LT1074)

#PE-92102 (LT1076)

HURRICANE

#HL-AK147QQ (LT1074)

#HL-AG210LL (LT1076)

RIPPLE CURRENT RATING

*

**

†

LT1074•TA01

25V

OUTPUT LOAD CURRENT (A)

0

60

70

80

90

12

3

4

LT1074•TPC27

5

6

100

50

L = 50

µH TYPE 52 CORE

DIODE = MBR735

V

= 5V, V

= 15V

OUT

IN

V

= 12V, V

= 20V

OUT

IN

LT1074