LMR14050-Q1: Necessity for soft start capacotor

Rod Brick

Part Number: LMR14050-Q1
Other Parts Discussed in Thread: LMR14050

What is the effect if no soft start capacitor is installed which the datasheet says limits inrush current. My power supply is fed by mains, the 18VAC secondary is rectified and feeds 5400uF, so it seems power-on inrush current to the LMR14050 would be minimal or zero because the bulk filter capacitors would absorb it all. But, if the LMR14050 is disabled during operation there could be some inrush current depending on the load when the LMR14050 becomes again enabled. Would this cause a deleterious effect in the LMR14050?

over 5 years ago

0 Frank De Stasi over 5 years ago

TI__Guru 72315 points

It is always best to have a soft-start on a DC/DC. Not only does this help to prevent in-rush current

but also can help reduce overshoot of the output voltage when starting up. There should be no damaged

to the device without a soft-start. I would leave a space on the PCB for a soft-start capacitor and leave it as "don't populate"

in case you need it later.

0 Rod Brick over 5 years ago in reply to Frank De Stasi

Intellectual 580 points

Thanks Frank. My problem is self-generated and construction, not design. I am replacing the LMR14050 for the third time, and the previous unsoldering damaged a couple of feed traces; the one that feeds the soft start capacitor is nigh on unrepairable.