LM5164-Q1: CISPR-25 Class-3 failed

Subhash Dhyani

Part Number: LM5164-Q1
Other Parts Discussed in Thread: LM5164

Dear CC,

In our BMS board we have used LM5164 device. This circuit is design for 12V/1A. But nominal current is only 50mA.

During conducted emission test this is failed even we have removed BMS PCB load (MCU and other peripherals). we have connected fixed 100 Ohm resistance at output.

Could you please help to pass this buck converter in CISPR Class 3. I have tuned input EMI filter and output snubber circuit but there is no much benefit.

this is urgent and solution is needed on an urgent basis.

Please see the attached schematics and failed frequency range and graph.

12V_1Amp Dc-Dc converter.pdf

Conducted emission failed at 535KHz to 710 KHz range.pdf

Thanks and regards

Subhash Dhyani

8 months ago

0 Joshua Austria 8 months ago

TI__Expert 6535 points

Hi Subhash,

Thank you for your question. I will take a look at your schematic. In the meantime, can you please send over your layout as well as this is critical to review for EMI performance.

Thank you,

Joshua Austria

0 Subhash Dhyani 8 months ago in reply to Joshua Austria

Intellectual 270 points

HI Joshua,

Thanks for your reply.

Please see the attached ppt for power section of six layer BMS board.

Please suggest some improvement. here and also suggest some improvement in existing board as well.

early reply is highly appreciated.

Thanks and regards

Subhash Dhyani

4555.POWER SECTION LAYOUT.pptx

0 Joshua Austria 8 months ago in reply to Subhash Dhyani

TI__Expert 6535 points

Hi Subhash,

I had a quick question about your schematic.

What is the upper trace from the RON pin going to? I was unable to locate this component in your schematic.

Additionally, please download this calculator and fill it out with your operating conditions as it will give us a better insight as to what there is best to do about your schematic/layout.

Thank you,

Joshua Austria

0 Subhash Dhyani 7 months ago in reply to Joshua Austria

Intellectual 270 points

Hello, Joshua,

A ICT test point is there from RON PIN.

We have tried with all calculated value in xls but no improvement.'

thanks and regards

Subhash Dhyani

0 Joshua Austria 7 months ago in reply to Subhash Dhyani

TI__Expert 6535 points

Hi Subhash,

Please send your calculator that you filled out.

Additionally, I noticed that your inductor has a bit of a larger size. Can you try with a different inductor that you could use with a smaller size? Sometimes having a large size inductor can negatively affect conducted emissions and actually cause some circuits that would otherwise pass to not.

Thank you,

Joshua Austria

0 Joshua Austria 7 months ago in reply to Joshua Austria

TI__Expert 6535 points

Hi Subhash,

I am closing this thread due to inactivity. Please feel free to open it if you need assistance.

Thank you,

Joshua Austria

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LM5164-Q1: CISPR-25 Class-3 failed