Inductor selection for DC to DC buck converter LM73606

[Calex]

Hello everyone!

On my analysis have come up with the following ratings for my inductor: L = 6.94uH with I_MAX > 9.85A. I wonder how I should select a proper component for my circuit as with those ratings it's been difficult to find the suitable one, especially when trying to balance both values of Inductance and Current rating. But also which type of inductor suits the Converter? which factors or parameters should I consider in addition to Inductance and current rating?

[Steve.Picotest]

This is complex. These ratings relate to temperature rise and inductance droop. There are shielding options that impact EMI as well as cure temperature and overcurrent protection issues. Many larger inductor manufacturers can help select, or design the appropriate inductor for your application.

For lowest noise, consider a toroidal inductor, many manufacturers offer these.

[Calex]

Okay, thank you for the advice, Steve!

[Steve.Picotest]

You bet . Feel free to ask more questions as you navigate this.

[Calex]

I'll never miss a chance!

[karimoviç]

hello , i think that the table in page 27 on the datasheet can help you . lm73606.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&DCM=yes&ref_url=https%3A%2F%2Fwww.mouser.fr%2F&distId=26.pdf

[Calex]

Thank you very much Karimovic, this too has helped me!

[Steve.Picotest]

The datasheet is pretty much worthless. Provides some basic guidance, but it isn't that simple. For example what about SRF. AC loss. Shielding and EMI? Most inductor datasheets don't. Include that info either.

[Calex]

I see! what about WEBENCH from TI? Is it worthwhile?

[Steve.Picotest]

We bench is OK, so long as the models are good. I did many of the older models. Webench won't limely have decent inductor models. I did publish an inductor model with saturation about 30byrs ago. It didn't include AC losses or shielding effect. I am working with Keysight on that now for their ADS simulator

[Calex]

Okay!  Very interesting! Therefore I am chatting with the Power supply Guru 😊! Looking forward to sharing more with you!

[Steve.Picotest]

Happy to help when I can. My articles on inductors are old, but the inductor model is also in my switchmode book that was re-released on Amazon

[Calex]

What's the name of the book, Please?

[Steve.Picotest]

https://www.amazon.com/Switched-Mode-Power-Supply-Simulation-SPICE/dp/1941071848/ref=sr_1_2?dchild=1&keywords=switched-mode&qid=1612123610&sr=8-2

[Calex]

The book looks very practical indeed! oh! Now I got you! I saw you recently on LinkedIn as Robert posted about a certain book from Picotest. Nice to meet you, Steve!

[Steve.Picotest]

nice to meet you too

[robertferanec]

A good start is always have a look on the chip manufacturer development board BOM:

https://www.ti.com/tool/LM73606EVM-5V-400K

https://www.ti.com/lit/ug/snvu579/sn...606EVM-5V-400K

Looks like they used XAL7070-682MEB
https://www.coilcraft.com/en-us/prod...0/xal7070-682/

[Calex]

Thank you, Robert! This has increased my design resource to be consulted now and then!

[Steve.Picotest]

Robert, only if you trust the chip manufacturer to choose a good one

[Calex]

As TI used the chip for evaluation does it not promote trust at least for me who I'm not much aware of many manufacturers?

[Steve.Picotest]

Calex, in some case, perhaps. Having tested 100's of these evaluation boards, and am not generally a fan. They are often created by interns and I have seen many that are pretty hideous. It could be a good starting place unless it isn't. I'll try to write an article about inductor selection soon.

The magnetics manufacturers will likely be more help, but there are still many dependencies. What are the goals? Max performance or min cost? Min size or min EMI? SRF? Shortest lead time? There are generally many competing factors. SRF (self resonant frequency) is generally an important factor and many datasheets don't even include it. Same with AC losses.

[Calex]

I'm eagerly waiting for the article, Steve!

[Calex]

In case you have any old but gold article about this, I'll be thankful to learn from it also as I'm waiting.

[Steve.Picotest]

Calex, will do. I started the article today, looked up this part and ordered the EVAL board. As always, most is ignored in the TI datasheet and also in the XAL7070 inductor datasheet...

[Calex]

This is good news! 🙂