CMS06 datasheet(13/63 Pages) NISSHINBO

13 / 63 page

R1245x

No. EA-269-240903

Ripple Current and Lx Current Limit

The ripple current of the inductor may change according to the various reasons. In the R1245x, as an Lx

current limit, Lx peak current limit is used. Therefore the upper limit of the inductor current is fixed.

The peak current limit is not the average current of the inductor (output current). If the ripple current is large,

peak current becomes also large. The characteristic is used for the fold-back current limit of version B/D/F/H.

In other words, the peak current limit is maintained and the switching frequency is reduced, as a result, the

average current of the inductor is reduced. To release this condition, at 170 kHz for version B/D, at 250 kHz

for version F, at 400 kHz for version H must not be beyond the peak current limit. In the figure1, the sequence

of the Lx current limit function is described.

VOUT

short

4msec

shutdown

restart

(CE=0→"H")

short

open

FB<0.56V

VOUT

IOUT

VOUT

IOUT

FB<0.56V

Limit Latch

(R1245x00x

A/C/E/G)

Fold Back

(R1245x00x

B/D/F/H)

shutdown

4msec

Figure 1. LX Limit function sequence

CMS06 Datasheet(PDF) 13 Page - Nisshinbo Micro Devices Inc.