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APPLICATION INFORMATION

Layout Guidelines

LM2575

(ADJ)

100

µF

+

16

5, 12, 13

GND

9 ON/OFF

D1

11DQ06

OUTPUT

3

L1

330

µH

330

µF

+

FEEDBACK

7

L

O

A

D

7-V to 60-V

Unregulated

DC Input

Adjustable Output Voltage Versions

Where

R1 = 2 kW

R2 = 6.12 kW

R2

R1

Input Capacitor (C

I

C,RMS

u 1.2(

T

) I

T

+

V

OUT

V

IN

{buck regulator}, and

T

+

|V

(|V

{buck−boost regulator}

Output Capacitor (C

LM2575

1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR

SLVS569E – JANUARY 2005 – REVISED JANUARY 2006

With any switching regulator, circuit layout plays an important role in circuit performance. Wiring and parasitic

inductances, as well as stray capacitances, are subjected to rapidly switching currents, which can result in

unwanted voltage transients. To minimize inductance and ground loops, the length of the leads indicated by

heavy lines (see Figure 1) should be minimized. Optimal results can be achieved by single-point grounding or by

ground-plane construction. For the same reasons, the two programming resistors used in the adjustable version

should be located as close as possible to the regulator to keep the sensitive feedback wiring short.

Figure 1. Test Circuit and Layout Guidelines

possible to the regulator. For operating temperatures below –25

°C, C

addition, since most electrolytic capacitors have decreasing capacitances and increasing ESR as temperature

drops, adding a ceramic or solid tantalum capacitor in parallel increases the stability in cold temperatures.

To extend the capacitor operating lifetime, the capacitor RMS ripple current rating should be:

For both loop stability and filtering of ripple voltage, an output capacitor also is required, again in close proximity

to the regulator. For best performance, low-ESR aluminum electrolytics are recommended, although standard

aluminum electrolytics may be adequate for some applications. Based on the following equation:

5