Test Circuit and Layout Guidelines
Fixed Output Voltage Versions
DS012565-22
C
IN
— 120 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”
C
OUT
— 120 µF, 25V Aluminum Electrolytic, Nichicon “PL Series”
D1 — 3A, 40V Schottky Rectifier, 1N5822
L1 — 100 µH, L29
Adjustable Output Voltage Versions
DS012565-23
C
IN
— 120 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”
C
OUT
— 120 µF, 25V Aluminum Electrolytic, Nichicon “PL Series”
D1 — 3A, 40V Schottky Rectifier, 1N5822
L1 — 100 µH, L29
R
1
— 1 kΩ, 1%
C
FF
— See Application Information Section
FIGURE 1. Standard Test Circuits and Layout Guides
As in any switching regulator, layout is very important. Rap-
idly switching currents associated with wiring inductance can
generate voltage transients which can cause problems. For
minimal inductance and ground loops, the wires indicated by
heavy lines should be wide printed circuit traces and
should be kept as short as possible.
For best results, ex-
ternal components should be located as close to the
switcher lC as possible using ground plane construction or
single point grounding.
If
open core inductors are used,
special care must be
taken as to the location and positioning of this type of induc-
tor. Allowing the inductor flux to intersect sensitive feedback,
lC groundpath and C
OUT
wiring can cause problems.
When using the adjustable version, special care must be
taken as to the location of the feedback resistors and the as-
sociated wiring. Physically locate both resistors near the IC,
and route the wiring away from the inductor, especially an
open core type of inductor. (See application section for more
information.)
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