LM2670 datasheet(11/26 Pages) NSC

11 / 26 page

Application Hints (Continued)

DESIGN CONSIDERATIONS

Power supply design using the LM2670 is greatly simplified

by using recommended external components. A wide range

of inductors, capacitors and Schottky diodes from several

manufacturers have been evaluated for use in designs that

cover the full range of capabilities (input voltage, output

voltage and load current) of the LM2670. A simple design

procedure using nomographs and component tables pro-

vided in this data sheet leads to a working design with very

little effort. Alternatively, the design software, LM267X Made

Simple (version 6.0), can also be used to provide instant

component selection, circuit performance calculations for

evaluation, a bill of materials component list and a circuit

schematic.

The individual components from the various manufacturers

called out for use are still just a small sample of the vast

array of components available in the industry. While these

components are recommended, they are not exclusively the

only components for use in a design. After a close compari-

son of component specifications, equivalent devices from

other manufacturers could be substituted for use in an ap-

plication.

Important considerations for each external component and

an explanation of how the nomographs and selection tables

were developed follows.

INDUCTOR

The inductor is the key component in a switching regulator.

For efficiency the inductor stores energy during the switch

ON time and then transfers energy to the load while the

switch is OFF.

Nomographs are used to select the inductance value re-

quired for a given set of operating conditions. The nomo-

graphs assume that the circuit is operating in continuous

mode (the current flowing through the inductor never falls to

zero). The magnitude of inductance is selected to maintain a

10094207

FIGURE 1. Basic circuit for fixed output voltage applications.

10094208

FIGURE 2. Basic circuit for adjustable output voltage applications

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