LMR36015: EMC issues

Armin P

Part Number: LMR36015
Other Parts Discussed in Thread: BQ25302,

Tool/software:

Hi everyone,
I mounted the LMR36015BRNX step-down converter on a 4-layer PCB. It is a handheld device equipped with a single lithium polymer cell.

During the usual CE EMC measurements in the lab, I failed the radiation test and the cable-connected feedback test.
I determined the main cause to be the BQ25302, and asked for help in the following thread.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1421283/bq25302-emc-issues

I also suspect relevant interference signals from the LMR36015BRNX. This is also the IC closest to the device input/output.

Does anyone have suggestions for solutions?
What are the relevant components in the circuit diagram and layout to keep interference signals to a minimum?

11 days ago

0 Armin P 11 days ago

Prodigy 20 points

SCHEMATIC

BOTTOM LAYER (mirrored view)

BOTTOM VIEW

WIRED FEEDBACK SIGNAL

RADIATION SIGNAL

0 Richard Fu22 10 days ago in reply to Armin P

TI__Mastermind 22740 points

Hi Armin,

Usual factors that occur are switched currents and large current loops which can propagate radiated EMI.

One thing you could look at is the input current loop and making sure that it is as tight as possible and the SW node. From my point of view, it looks like you've followed the layout guidelines of the LMR36015 quite well so it may be due to U3 device.

You may also try adding an input EMI filter as well. A pi-filter may be a good starting point, I would recommend following a butterfly layout.

https://www.ti.com/lit/an/slua929a/slua929a.pdf?ts=1728598221694&ref_url=https%253A%252F%252Fwww.google.com%252F

Thanks,

Richard

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LMR36015: EMC issues