LM25148: LM25148

Ali Khan

Part Number: LM25148

Hi,

I designed the board and got PCB review as well before fabrication. Now when i did some testing and found an issue.
If load current is above 10A then circuit don't work. I can also hear the inductor noise coming out of it.
Can someone help me with it plz?
Thanks
Aurora Tie

Orlando Murray

6 months ago

0 Ali Khan 6 months ago

Intellectual 890 points

Just to add here,
If i linearly increase load current step by step from low value to above 10A then sometimes it works and sometimes it won't.
Also i noticed that MOSFET temperature rises about 70C in 2 minutes of continues 10A load current.
The input voltage are 16.8V and output is 8.4V at 10A load current.
Thanks

0 David Baba 6 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Hello Ali,

Can you please post your schematic and also please fill out the calculator spreadsheet with your requirements.

LM5148-LM25148 Quickstart Calculator.xlsm

Thanks,

David.

0 Ali Khan 6 months ago in reply to David Baba

Intellectual 890 points

Hi David Baba
I can send you both files in private if possible.
Thanks

0 Ali Khan 6 months ago in reply to David Baba

Intellectual 890 points

8037.LM5148-LM25148 Quickstart Calculator.xlsm

I used Webench and some suggestions from TI expert. I filled up this calculator as much i can understand. I also message you schematic.
Let me know if you have any questions.

Thanks

0 David Baba 6 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Hello Ali,

From your inputs your inductance value is too low. I have modified the calculator and suggest you follow the values I have in there, in particular the inductance value, the Rsense values and also the compensation values. Hope this helps.

8037.LM5148-LM25148 Quickstart Calculator dsb edits.xlsm

David

0 Ali Khan 6 months ago in reply to David Baba

Intellectual 890 points

Hi David Baba

My design was based on Webench.
https://webench.ti.com/power-designer/switching-regulator/customize/103?VinMin=9&VinMax=36&O1V=7.4&O1I=12&base_pn=LM25148&AppType=None&Flavor=None&op_TA=30&origin=pf_panel&lang_chosen=en-US&optfactor=3&Topology=Buck&flavor=None&VoltageOption=None

Do you think, it wasn't the right?

0 David Baba 6 months ago in reply to Ali Khan

TI__Mastermind 29310 points

According to the Calculator, When I checked your inputs, your design is not correct Ali,

Not sure what was inputted in the WEBENCH, for example WEBENCH will not let you design to 100kHz switching frequency.

When I try to follow the link you provided there is an error in the design parameters specified. Suggest you follow the guidance in the spreadsheet I provided, if you have some concern, please feel free to reopen thread to discuss.

Hope this helps,

David.

0 Ali Khan 6 months ago in reply to David Baba

Intellectual 890 points

Hi David Baba
I appreciate your help. I simply want to explore the mistake that i made in the process before fabrication so i can avoid it in the future.
Here are the steps that i followed.
1: Used Webench Design

2: Got Schematic review from TI expert and fixed issues.
3: Got PCB reviews from TI expert and fixed issues.

Then i went to fabrication and now i am facing this issue.

Now about the next steps,
I will follow that calculator to update design but i have some questions if you can help me to understand in a best possible way.

1: How i can completely understand EXTCOMP feature?
2: What other specs i should consider while designing this high current converter? I need 7.7/8.4V 12 to 15A converter

Thanks

0 Ali Khan 6 months ago in reply to Ali Khan

Intellectual 890 points

1738.WBDesign103.pdf

0 Ali Khan 6 months ago in reply to Ali Khan

Intellectual 890 points

One more thing, i want to add before selecting lower switching frequency is the size of the board.
I need very small size board as possible with following requirements.
1: Vin 9V to 36V
2: Vout 7.4/8.4V 12 to 15A

Size of the board = 17x35mm

Thanks

+1 David Baba 6 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Hello Ali,

I suggest using the external compensation, that way you can tune your loop as you need. internal compensation allows you to save of a few components, if that's not important go ahead and use EXT comp.

I created a WEBENCH design for you to follow its optimized for smallest footprint, please follow this design. Note that the higher the switching frequency the worse the losses.

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=1228274C63FD8A00

David.

0 Ali Khan 5 months ago in reply to David Baba

Intellectual 890 points

Hi David Baba
Thanks for the link,
I checked the new design, the only difference is inductor value and current sense resistor value.

Is there a way that i can have smaller size inductor?
Like this
https://www.digikey.com/en/products/detail/abracon-llc/ASPI-1367-2R2M-T/2343315

The idea size is 10x10x7mm.
Previously, I used this inductor.

Also, in your design, it is internal compensation.
Can you recheck because i can use external if it increase efficiency and reliability.
Thanks

0 David Baba 5 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Hello Ali,

the design I am suggesting is using external compensation. as far as the inductor is concern, need to use the inductor value suggested 2.2uH and 32A Isat, this should work fine.

Hope this helps,

David.

0 Ali Khan 5 months ago in reply to David Baba

Intellectual 890 points

Hi David Baba
I just want to conclude this thread. Can you give your concluded remarks what was the issue that you think caused my circuit to not work above 10A?
Here is the Webench design report that i downloaded for my previous design.
Also, i couldn't find complete detail about EXTCOMP circuit and how we can define each component value?
I know i can use WEBENCH to get some values but how we can manually choose this parameters?
WBDesign103 (1).pdf

0 David Baba 5 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Hello Ali,

If you when with the recommended values in webench and it was working well up to 10A, you may have had noise on the current sense, you can try reducing Rsense a little and see if that helps.

As for calculating manually, details of compensation are given in the datasheet, but suggest use the quickstart file for recommended values.

Hope this helps.

David.

0 Ali Khan 5 months ago in reply to David Baba

Intellectual 890 points

The very first problem is noise coming out of the inductor above 10A. What cause this issue?
Second, rise of temperature that is not important at this stage of development but need to address.

0 David Baba 5 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Hello Ali,

The noise is possibly caused layout. did you route the current feedback differentially? If not, noise can couple onto the current feedback trace.

Can you detail what your second issue is you are referring to please?

Thanks.

David.

0 Ali Khan 5 months ago in reply to David Baba

Intellectual 890 points

Hi,
Can you give me pcb layout review to find the issue?
I can share files in private
Thanks

0 David Baba 5 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Hello Ali,

We provide detailed guidelines in the datasheet. You can compare your layout to the details therein. Also, please compare your layout to the concept diagram below. If you layout is not compliant to the recommendations above, this would be my feedback should you share with me privately.

Thanks.

David.

0 Ali Khan 5 months ago in reply to David Baba

Intellectual 890 points

i didn't route differential these tracks.
So what i will do. I will route it again with these details then i will need pcb design review from a TI expert like always.
I will follow your WEBENCH design for this version and hopefully after all these reviews, it will work.
Thanks

0 David Baba 5 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Sure Ali,

feel free to open new thread when ready, thanks.

David.

0 Ali Khan 5 months ago in reply to David Baba

Intellectual 890 points

Hi David Baba
Can you tell me where i can find above picture information on datasheet?
Also what is the impedance value for differential pair routing of these tracks?

0 David Baba 5 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Hello Ali,

It's all about minimizing the parasitic inductance to a minimum. please route differentially, see below screen shot of the differential pair for current sense in the EVM user guide.

LM25149-Q1 EVM User's Guide (Rev. A) (ti.com)

Hope this helps.

David.

0 Ali Khan 5 months ago in reply to David Baba

Intellectual 890 points

Hi David Baba
In the EVM schematic, there are a resistor and capacitor connected with RSENSE resistor while in the WEBENCH design, there are not present.
Should i add them?

0 David Baba 5 months ago in reply to Ali Khan

TI__Mastermind 29310 points

Hello Ali,

Yes, please add, you can always DNP if not needed.

Thanks,

David.

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LM25148: LM25148