LMR43620: The design from Webench Power Design does not match the latest datasheet. Want to know which one is correct.

Hello

I will ask the Application engineer for this product to help answer your questions.

Thanks

Hello,

Thank you for highlighting this. The datasheet revised Dec. 2021 is the most up-to-date, the version revised in October 2021 is still in the Advanced Information stage and will be revised to match the other version once these devices are released. 

Please refer to the datasheet revised Dec. 2021 for the correct RFBT and RFBB configuration values. In terms of the External UVLO resistors, again please use the datasheet revised Dec. 2021. 

The input filter caps, output caps and inductor selected by Webench should be correct. If you share the link to your design here I will confirm.

Regards,

Harrison 

Harrison,

I had sent you the link. do you have a chance to take a look? Thanks

Hi Rong,

I don't see the link anywhere. 

Could you copy-paste the link here in this post? 

Regards,

Harrison

Harrison,

Below is the link

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=56DB0B00D689274A

Thank you

Hi Rong,

Thanks for sending the link. 

It looks like the input capacitance is lower than I would suggest. Try using a 4.7uF input capacitor instead.

In terms of Cout, I think it would be a good idea to add another footprint in your board layout to accommodate an extra output cap to optimize load transient performance during your initial testing. 

Let me know if you have any further questions. 

Regards,

Harrison

Hi Harrison,

Thank you. I will change them. For Lf_inpflt and L1, are they OK?

Rong 

Harrison,

I was planning to use fixed 3.3V output version, but Webench power design warned the 3.3V fixed output is not stable based on my input and output condition. 

Rong

Hi Rong,

L1 seems ok, but 2.2uH or 3.3uH would result in less inductor current ripple ad therefore less output voltage ripple. In terms of the EMI filter I would use the filter offered on page 37 of the datasheet for the LMR43620-Q1. 

I am sorry you are having difficulties with this webench model. I will need to look into this with our Webench team further to get to the bottom of this. 

In the mean time, I'll point you to our evaluation module (EVM) for this device. The EVM offers an example schematic that you can use to base your design off of. We also offer the EVM design files that you can import into your PCB editing software to get started with your design. 

LMR43620-Q1 EVM User's Guide (Rev. B) (ti.com)

snvc247.zip

Regards,

Harrison 

Harrison,

Thanks for the reply. I noticed the EVK was released in Nov 2021, but the latest datasheet was released in Dec 2021. I want to know if the design on EVK matches the current production chip? 

Thanks

Rong

Hi Rong,

Yes the design of the EVM matches the current production chip. 

Regards,

Harrison 

Harrison,

Thank you.

Rong

Thank you. I am fine now and will come back if I have problem or need help.

Regards

Rong