IRU3072C datasheet(13/24 Pages) IRF

13 / 24 page

IRU3072

Rev. 1.0

3/25/04

www.irf.com

FS = FS(NOM)

Therefore, the output current limit threshhold is set by:

Where:

From equation (2), the over current limit set resistor can

be calculated by:

Where RDS(ON) has to choose the maximum over the tem-

perature for the selected MOSFET. Overall, the profile of

current limit operation is shown in Figure 17.

Figure 17 - Profile of operation switching frequency

versus output current.

(a). Normal operation.

(b). Current limit mode.

Figure 18 - Operation waveforms during normal

and current limit mode.

DIPK_PK(LIM)=

(VIN-VO(NOM))

3VO(NOM)

(VIN

3FS(NOM)3L)

IOUT(LIM) =I SET +

DIPK_PK(LIM)

RSET =

ISET

3RDS(ON)

RSET = (IOUT(LIM)-

DIPK_PK(LIM)/2)3RDS(ON)/20mA ---(3)

IO(MAX)

IO(LIM)

Switching

Frequency

IOUT

FS(NOM)

Normal

Operation

Over

Current

Limit

Mode

Shutdown

by UVLO

ISET

Select inductor L, frequency FS(NOM), IO(LIM)

Set: ISET = IO(LIM)-

∆IPK_PK/2

Select: RSET = ISET

3 RDS(ON)/20m A

(VIN-VO(NOM))

3 VO(NOM)

VIN

3 L3 FS(NOM)

Calculate:

∆IPK_PK(LIM) =

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