UCC3945 datasheet(7/11 Pages) ETC1

7 / 11 page

UCC2941-3/-5/-ADJ

UCC3941-3/-5/-ADJ

1.0V input.

Inductor Section

An inductor value of 22

µH will work well in most applica-

tions, but values between 10

µH and 100µH are also ac-

ceptable. Lower value inductors typically offer lower ESR

and smaller physical size. Due to the nature of the

“bang-bang” controllers, larger inductor values will typi-

cally result in larger overall voltage ripple, because once

the output voltage level is satisfied the converter goes

discontinuous, resulting in the residual energy of inductor

causing overshoot.

It is recommended to keep the ESR of the inductor below

0.15

Ω for 500mW applications. A Coilcraft DT3316P-223

surface mount inductor is one choice since it has a cur-

rent rating of 1.5A and an ESR of 84m

Ω. Other choices

for surface mount inductors are shown in Table 1.

Output Capacitor Selection

Once the inductor value is selected the capacitor value

will determine the ripple of the converter. The worst case

peak to peak ripple of a cycle is determined by two com-

ponents, one is due to the charge storage characteristic,

and the other is the ESR of the capacitor. The worst case

ripple occurs when the inductor is operating at maximum

current and is expressed as follows:

()

∆V

ESR

•

••

−

+•

where

ICL = the peak inductor current I

Power Limit













∆V = output ripple

VO = output voltage

VI = input voltage

CESR = ESR of the output capacitor

A Sanyo OS-CON series surface mount capacitor

(10SN100M) is one recommendation. This part has an

ESR rating of 90m

Ω at 100µF. Other potential capacitor

sources are shown in Table 2.

Input Capacitor Selection

Since the UCC3941 family does not require a large de-

coupling capacitor on the input voltage to operate prop-

erly, a 10

µF capacitor is sufficient for most applications.

Optimum efficiency will occur when the capacitor value is

large enough to decouple the source impedance. This

usually occurs for capacitor values in excess of 100

µF.

APPLICATION INFORMATION (cont.)

MANUFACTURER

PART NUMBER

Sanyo Video

Components

San Diego, California

OS-CON Series

Tel: 619-661-6322

Fax: 619-661-1055

AVX

Sanford, Maine

TPS Series

Tel: 207-282-5111

Fax: 207-283-1941

Sprague

Concord, New Hampshire

695D Series

Tel: 603-224-1961

Table 2. Capacitor Suppliers

MANUFACTURER

PART NUMBERS

Coilcraft

Cary, Illinois

DT Series

Tel: 708-639-2361

Fax: 708-639-1469

Coiltronics

Boca Raton, Florida

CTX Series

Tel: 407-241-7876

Table 1. Inductor Suppliers

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