Test Circuit and Layout Guidelines (Continued)
Adjustable Output Voltage Versions
01258323
where V
= 1.23V
REF
Select R to be approximately 1 kΩ, use a 1% resistor for best stability.
1
C
C
— 470 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”
— 220 µF, 35V Aluminum Electrolytic, Nichicon “PL Series”
IN
OUT
D1 — 5A, 40V Schottky Rectifier, 1N5825
L1 — 68 µH, L38
R1 — 1 kΩ, 1%
C
— See Application Information Section
FF
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,
external components should be located as close to the
switcher lC as possible using ground plane construction or
single point grounding.
When using the adjustable version, special care must be
taken as to the location of the feedback resistors and the
associated 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.)
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 COUT wiring can cause problems.
9
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