DESIGN CONSIDERATIONS
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FIGURE 1. Basic circuit for fixed output voltage applications.
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FIGURE 2. Basic circuit for adjustable output voltage applications
Power supply design using the LM2676EP is greatly simpli-
fied by using recommended external components. A wide
range of inductors, capacitors and Schottky diodes from sev-
eral manufacturers have been evaluated for use in designs
that cover the full range of capabilities (input voltage, output
voltage and load current) of the LM2676EP. A simple design
procedure using nomographs and component tables provided
in this data sheet leads to a working design with very little
effort. Alternatively, the design software, LM267X Made Sim-
ple (version 6.0), can also be used to provide instant compo-
nent selection, circuit performance calculations for evalua-
tion, a bill of materials component list and a circuit schematic.
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 required
for a given set of operating conditions. The nomographs as-
sume 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 maximum
ripple current of 30% of the maximum load current. If the ripple
current exceeds this 30% limit the next larger value is select-
ed.
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 compo-
nents are recommended, they are not exclusively the only
components for use in a design. After a close comparison of
component specifications, equivalent devices from other
manufacturers could be substituted for use in an application.
The inductors offered have been specifically manufactured to
provide proper operation under all operating conditions of in-
put and output voltage and load current. Several part types
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200996 Version 2 Revision 3 Print Date/Time: 2011/03/24 16:39:24
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