Test Circuit and Layout Guidelines (Continued)

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.

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

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.)

Adjustable Output Voltage Versions

where VREF = 1.23V

Select R1 to be approximately 1 kΩ, use a 1% resistor for best stability.

CIN

— 470 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”

COUT

— 220 µF, 35V Aluminum Electrolytic, Nichicon “PL Series”

D1

— 5A, 40V Schottky Rectifier, 1N5825

L1

— 68 µH, L38

R1

— 1 k

Ω,1%

CFF

— See Application Information Section

FIGURE 1. Standard Test Circuits and Layout Guides

9

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UMW LM2575/LM2575HV

UMW LM2575/LM2575HV