LM25037 / soft stop

Kensuke,

I think that the soft-stop description text appears to be missing from the datasheet. However, the function is listed in the electrical table and is shown in the block diagram on page 9.

Basically, when the controller enables (UVLO pin > enable threshold), the SS cap is slowly charged through 100 uA, as the SS pin level rises slowly, so too the PWM duty cycle is increased slowly in proportion.

During soft-stop (e.g. if UVLO pin < disable threshold), the PWM does not immediately stop in an abrupt fashion. Instead, the SS cap is slowly discharged through a similar 100 uA current sink, so as the SS cap voltage then falls at a controlled rate, so too does the PWM duty cycle, in proportion. This is the soft-stop feature, it forces a controlled ramp down of PWM duty cycle.

I hope this helps explain the feature. Please click on the link if this answers your question.

Thanks,
Bernard