LM5008A: LM5008A - non smooth startup

Jason Dai

Part Number: LM5008A

Dear E2E,

we are suffering non smooth startup issue. We found that it is due to Vin startup too slow because RT/SD pin is tie to Vin through resistor.

so, we try to fast up Vin then Vout is more smooth startup.

However, there are no extra circuit in customer board to hold SD pin to low until Vin get ready. Could we add cap on RT/SD pin to ground to delay EN time so that Vin goes higher a little to reduce this phenomenon?

over 5 years ago

0 Frank De Stasi over 5 years ago

TI__Guru 52765 points

I would not use a C directly on this pin. It is used for the timing control and may cause

some instibility to the internal circuit. I would try a FET from this pin to ground and put the

RC delay components on the gate.

0 Jason Dai over 5 years ago in reply to Frank De Stasi

TI__Expert 3720 points

Hi Frank,
As i mentioned, customer won't have extra component to get delay control EN pin.
except it, any other way can fix non-smooth startup issue?

Jason

0 Jason Dai over 5 years ago in reply to Jason Dai

TI__Expert 3720 points

Frank,
except adding delay circuit to control FET and then control EN pin, any other way?
customer doesn't have extra circuit to control it, but they don't want to see non-smooth startup waveform.

BR,
Jason

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LM5008A: LM5008A - non smooth startup