'i

2

x 1.1

'i

2

x 1.1

L =

'i

x

D

f

ISENSE

ADJ

VIN

PGATE

FB

EN

LM3489

GND

PGND

1

2

3

4

5

6

7

8

R3

R4

R4

R3

LM3489

www.ti.com

SNVS443A – MAY 2006 – REVISED JUNE 2008

(8)

Figure 7. Adjustable UVLO

Design Information

Hysteretic control is a simple control scheme. However the operating frequency and other performance

characteristics highly depend on external conditions and components. If either the inductance, output

The best approach is to determine what operating frequency is desirable in the application and then begin with

INDUCTOR SELECTION (L)

The important parameters for the inductor are the inductance and the current rating. The LM3489 operates over

a wide frequency range and can use a wide range of inductance values. A rule of thumb is to use the equations

is:

−0.366726

The inductance can be calculated based upon the desired operating frequency where:

(9)

And

(10)

The inductor should be rated to the following:

(11)

The inductance value and the resulting ripple is one of the key parameters controlling operating frequency. The

second is the inductor ESR that contribute to the steady state power loss due to current flowing through the

inductor.

Copyright © 2006–2008, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: LM3489