VIPER26LD 310VDC to 15VDC Converter Design Issue

[AAdin.1]

Hi, 

I have used following STM reference design for the buck converter. When I power the circuit output doesn't stabilize. What am I missing?

This is from. STEVAL-IHM023V3

Here is my design.

Here is the layout

Best Regards.

 

[Peter BENSCH]

> When I power the circuit output doesn't stabilize.

What does it mean?

What is your load?

Regards
/Peter

[AAdin.1]

Output rises and collapses. There is no active load at startup state, when I supply 15V with my bench power supply output circuit draws 0.025Amps.

Best regards.

[Peter BENSCH]

The buck regulator must have a sufficient load, 50...100mA should always flow as a minimum.

Where have you connected the 15V - at the input of this regulator, which requires an AC of at least 80V at the input, which corresponds to about 110V peak voltage?

What is the saturation current of your inductor L2 and what the expected output current?

Regards
/Peter

[AAdin.1]

The regulator will supply current to motor controller IC and two relays (edit: there is 3V3 LDO for MCU), there is no steady current at the startup. The supply voltage of the Viper is 310VDC. 

When I mentioned 15V from bench supply I checked the output of the Viper whether there is a short-circuit or not. 

Do you recommend dummy load for testing? 

Thank you for your time, I appreciate it.

Regards.

[Peter BENSCH]

Yes, I recommend a dummy load and also a test with a normal input voltage, possibly with an isolating transformer for safety reasons. Then you can also view the output signal with a scope.