WEBENCH® Tools/LMZM33606: This design is not stable due phase margin either smaller than 35 or greater than 120

Hi Damiano,

We are able to replicate this issue and we are looking into the loop model of this device. We will get back to you on this.

Thanks & Regards,
Praveen 

Hi Praveen,

Thanks for your work!

I look forward to hearing from you.

Best regards

Damiano

Hi Praveen,

Do you have news?

Thanks

Best regards

I had the exact same issue in Webench for LMZM33606.
Unfortunately on the datasheet there is no mention of phase margins whatsoever, therefore I am not sure whether I should trust this simulation warning or not.

I hope this is cleared asap. Thank you.

Hi Domiano,

The effective value of the total output capacitor is coming out to be very low and hence it is causing a low phase margin. We are working on the component selection of the output capacitor (Cout). We will keep you updated on this.

Thanks & Regards,

Praveen  

Hi Domiano,

We are working on it. We will keep you updated on this.

Thanks & Regards,

Praveen 

Hi Praveen,

Thanks for your work!

I hope for good news.

Best Regards

Damiano

Hi Damiano,

We are updating the component selection. We will let you know once this issue is fixed.

Thanks & Regards,

Praveen

Hi Praveen,

i have bought the eavaluation board.

I have done some test with different Vin for 12Vout. The load is 50W.

In the following table you can find the measured voltage value.

It seems work good until 12.5Vin without voltage drop on Vout.

Below 12.5Vin appears a voltage drop on Vout until 11.7Vin when the power good signal goes down. 

Furthermore i have done another test to see the transient effects. 

The test consists in activating/disactivating the 50W load (1 second on - 1 second off) 13Vin - 12Vout.

In the image you can see the Vout when the load is activated (12.06 V) and when the load is deactivated (12.2V). 

It seems stable.

I have added a 470uF output capacitor to reduce the Vout voltage drop during transient load activation. 

What do you think about that? can you recommend further tests to do?

Thanks

Regards

Damiano

Hi Damiano,

It looks like the device is operating as expected. We recommend a conservative VINmin of Vout*1.1 and we are observing much better headroom in the above results.

Thanks & Regards,
Praveen

Hi Praveen,

Thanks for your work

Best regards

Damiano