Application information

AN1518

20/30

9.4

Short-circuit protection

In overcurrent protection mode, when the peak current reaches the current limit, the device

frequency to approximately one third of its nominal value (see Section 3.4: Current

protection). In these conditions, the duty cycle is strongly reduced and, in most applications,

this is enough to limit the current to ILIM. In any event, in case of heavy short-circuit at the

of external components) the current peak could reach values higher than ILIM. This can be

understood considering the inductor current ripple during the ON and OFF phases:

●

ON phase

Equation 28

●

OFF phase

Equation 29

inductor.

inductor is very small and it could occur that the current ripple in this phase does not

condition for an extended period, the external components (mainly the inductor and diode)

must be selected based on this value.

Figure 14.

I

L

∆

V

IN

V

out

–

DCR

L

I

•

–

()

L

--------------------------------------------------------------

T

ON

=

=

I

L

∆

V

D

V

out

–

DCR

L

I

•

–

()

L

------------------------------------------------------------

T

OFF

=

=