Functional description

L7987

18/37

DocID025589 Rev 3

Figure 8. OCP and frequency scaling

(400 mV typ.) the peak current limit threshold is reduced to 1/3 of the nominal value. This

additional feature helps to reduce the IC stress in case of output short-circuit.

threshold is restored. This fold back protection is disabled during the soft-start.

This kind of overcurrent protection is effective if the inductor can be completely discharged

during HS MOS turn-off time, in order to avoid the inductor current to run away. In case of

output short-circuit the maximum switching frequency can be computed by Equation 4.

Equation 4

duration, the maximum FSW frequency which avoids the inductor current run away in case

If the programmed switching frequency is higher than the above computed limit, an estimation

of the inductor current in case of output short-circuit fault is provided by Equation 5:

Equation 5

Equation 6

page 8.



8

 V

F



LIM

+



+



–

 I

LIM

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

1



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







–







 R

ON

+





+



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

=

20k



----------



=