LT1578CS8 datasheet(28/28 Pages) LINER

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LT1578/LT1578-2.5

PART NUMBER

DESCRIPTION

COMMENTS

LT1074/LT1076

Step-Down Switching Regulators

40V Input, 100kHz, 5A and 2A

LTC1174

High Efficiency Step-Down and Inverting DC/DC Converter

0.5A, 150kHz Burst Mode

TM Operation

LT1370

High Efficiency DC/DC Converter

42V, 6A, 500kHz Switch

LT1371

High Efficiency DC/DC Converter

35V, 3A, 500kHz Switch

LT1372/LT1377

500kHz and 1MHz High Efficiency 1.5A Switching Regulators Boost Topology

LT1376

High Efficiency Step-Down Switching Regulator

25V, 1.5A, 500kHz Switch

LT1507

High Efficiency Step-Down Switching Regulator

15V, 1.5A, 500kHz Switch

LT1676/LT1776

High Efficiency Step-Down Switching Regulators

7.4V to 60V Input, 100kHz/200kHz

LTC1772

SOT-23 Low Voltage Step-Down DC/DC Controller

550kHz, Drives PFET, 6-Lead SOT-23 Package; up to 4.5A Output Current

LTC1735

High Efficiency Step-Down Converter

Synchronous Buck Controller Drives External MOSFETs

LT1777

Low Noise Step-Down Switching Regulator

48V Input, Internally Limited dV/dt, Programmable di/dt

Burst Mode is a trademark of Linear Technology Corporation.

1578f LT/TP 0100 4K • PRINTED IN USA

©LINEAR TECHNOLOGY CORPORATION 1999

TYPICAL APPLICATION

Dual Output SEPIC Converter

The circuit in Figure 17 generates both positive and

negative 5V outputs with a single piece of magnetics. The

inductor L1 is a 33

µH surface mount inductor from

Coiltronics. It is manufactured with two identical windings

that can be connected in series or parallel. The topology for

the 5V output is a standard buck converter. The – 5V

topology would be a simple flyback winding coupled to the

buck converter if C4 were not present. C4 creates the

SEPIC (Single-Ended Primary Inductance Converter) to-

pology which improves regulation and reduces ripple

current in L1. Without C4, the voltage swing on L1B

compared to L1A would vary due to relative loading and

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408)432-1900 q FAX:(408)434-0507 q www.linear-tech.com

BOOST

LT1578

VIN

OUTPUT

–5V†

* L1 IS A SINGLE CORE WITH TWO WINDINGS

COILTRONICS CTX33-2

** AVX TSPD107M010

† IF LOAD CAN GO TO ZERO, AN OPTIONAL

PRELOAD OF 1k TO 5k MAY BE USED TO

IMPROVE LOAD REGULATION

INPUT

6V TO 15V

GND

1578 F17

0.33

µF

100pF

1N5818

C1**

100

µF

10V TANT

C5**

100

µF

10V TANT

µF

35V TANT

C4**

100

µF

1N914

15.8k

4.99k

1N5818

L1A*

µH

L1B*

VSW

GND

SHDN

RELATED PARTS

Figure 17. Dual Output SEPIC Converter

coupling losses. C4 provides a low impedance path to

maintain an equal voltage swing in L1B, improving regu-

lation. In a flyback converter, during switch on time, all the

converter’s energy is stored in L1A only, since no current

flows in L1B. At switch off, energy is transferred by

magnetic coupling into L1B, powering the – 5V rail. C4

pulls L1B positive during switch on time, causing current

to flow, and energy to build in L1B and C4. At switch off,

the energy stored in both L1B and C4 supply the – 5V rail.

This reduces the current in L1A and changes L1B current

waveform from square to triangular. For details on this

circuit see Design Note 100.

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