LM5021: How to deal pre-bias start up with LM5021?

Ray Chang

Intellectual 1345 points

Part Number: LM5021
Other Parts Discussed in Thread: TL431

Hi, Team

My customer has a flyback design fro DC/DC module, they are using the LM5021 as main controller on primary side.

We met an issue the output overshoot over 10% when the DC/DC module doing the ON/OFF testing fastly.

Could you let us know how to implement pre-bias function when system start up for LM5021?

over 7 years ago

0 Kuan Wei Chen (Kevin Chen) over 7 years ago

TI__Genius 9710 points

Dear Ray,

For solving the issue of the overshoot, increase the capacitance on the SS pin will be the easiest way.

Can you help me to increase this capacitor to check the over voltage decrease or not?

In the same time, I will also help you to find pre-bias circuit.

Best Regards

Kevin

0 Ray Chang over 7 years ago in reply to Kuan Wei Chen (Kevin Chen)

TI__Intellectual 1345 points

Hi, Kevin

In the normal start-up, the output voltage ramp smooth.
The capacitance of SS, we think the value should be fine.
But we found the overshoot will over spec when we did the rapid on/off testing,.

For the pre-bias circuit, do you have any recommend?