LM5021: not starting up.

Sankalp Gitaje

Prodigy 201 points

Part Number: LM5021

I am designing a flyback for below specs:

Vin: 100V to 280Vdc

PO:20W

Vo:17.3V

I have attached snapshot below, at power on I am getting the >8V at VIN pin but controller is not start switching. I am not getting any voltages at CSS or VCC pin. Can you please let me know what I am missing.

over 3 years ago

0 Sankalp Gitaje over 3 years ago

Prodigy 201 points

understood my mistake...Vin should be 20V typ.

0 Ulrich Goerke over 3 years ago in reply to Sankalp Gitaje

TI__Mastermind 40580 points

Hello Sankalp,

I'm glad that you were able to determine the issue and solve it yourself.

To be clear, Vin needs to rise up to 20V (typ, 23V max) first to start the IC, but does not need to stay there. After starting, VIn may drop to close to 7.25V, but for operating margin, Vin > 8V is a good idea.

Regards,
Ulrich

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LM5021: not starting up.