Test Circuit and Layout Guidelines (Continued)

where VREF = 1.23V

UNREGULATED

DC INPUT

Adjustable Output Voltage Versions

R2

LOCATE THE PROGRAMMING RESISTORS NEAR

THE FEEDBACK PIN USING SHORT LEADS

FEEDBACK

LM2596/

LM2596HV

ADJUSTABLE

GND 5 ON/OFF

OUTPUT

Select R, to be approximately 1 k2, 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 pH, L38

R1 -1 k2, 1%

CFF-See Application Information Section

HEAVY LINES MUST BE KEPT SHORT AND USE

GROUND PLANE CONSTRUCTION FOR BEST RESULTS

VOUT - VREF

R₂-R₁

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 IC as possible using ground plane construction or

single point grounding.

000

L1

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,

IC groundpath and Cour Wiring can cause problems.

D1

REF (1 + R₂)

YOUT

VREF

¹)

KEEP FEEDBACK WIRING AWAY

FROM INDUCTOR FLUX

REGULATED OUTPUT

Cour

FIGURE 1. Standard Test Circuits and Layout Guides

LOAD

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.)