WEBENCH® Tools/LM5164-Q1: Negative voltage, instability

Yngve Eriksen1

Part Number: LM5164-Q1

Tool/software: WEBENCH® Design Tools

Hi.

I have the following design from Webbench:

When implemented on our PCB, I cannot get it to be stable.

In plot below the lines are as follows, the input voltage is 12V 3Amp max, load is 3x4K ohm -> 30mA

Yellow: input voltage

Green: input current (wrong scale)

Red: Switching output

Blue: negative -40V (DCDC output)

Can anybody see any clear reason for the instability?

0 Marshall_Beck over 3 years ago

Unfortunately I am unable to see your attached images.

Can you please ensure that they were uploaded properly?

0 Yngve Eriksen1 over 3 years ago in reply to Marshall_Beck

Sorry,

Please see pictures here.

0 Marshall_Beck over 3 years ago in reply to Yngve Eriksen1

Hello,

Sorry for the delay. I was out-of-office.

I need to investigate this further.

I was able to replicate your webench, though, am unable to look at the loop response.

inverting buck boost topology brings in a RHP zero, causing difficulty sometimes in compensation.

You are most likely crossing over at low frequency. Some tuning of the output filter, or possible phase boost is needed.

Allow me to get back to you.

0 Frank De Stasi over 3 years ago in reply to Marshall_Beck

Hello

I am closing this post due to inactivity.

Thanks

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