LM5025A: PMP4468 - EMC Issue

Yue TANG

Part Number: LM5025A
Other Parts Discussed in Thread: INA159

Hi ,

My customer have used LM5025A for a long time, and TI design PMP4468 was exactly designed based on their requirement long time ago. their design closely followed this design and the BOM is exactly the same.

but this design has a electromagnetic radiation problem which have impacted their ADC[accuracy reduction] and their VGA interface[diplay interference]. This issue have last for a long time. they even designed a metal shield, but the improvement is small.

BTW, They tried to use a integrated power modules to replace LM5025A and the issue gone. so,They strongly suspect that this design has EMC problems.

Is there any expert who can help with some suggestions? How to reduce the interference? Thanks.

below is the schematic and part of PCB

GTS-800.rar

In PCB, I highlighted related symbols, You can find what is it from schematic:

U140 - LM5025A

U100 - ADS7229IPW

U98- ADG408 [Mux]

U101- INA159[Difference Amplifier]

over 5 years ago

0 Teng Feng over 5 years ago

TI__Genius 13660 points

Hi Yue Tang, an expert will get back to you soon.—— Teng

0 Teng Feng over 5 years ago in reply to Teng Feng

TI__Genius 13660 points

Hi Yue Tang,

Here are my several ideas:
1) please first check the ripple voltage of each IC's VDD.
2) The bead and filter capacitors are needed for each IC's power supply. and try to use different beads and filter caps for different frequency suppress.
3) Does the mentioned metal shielding covered whole power module? and if the shielding connected to ground?
another method you can try is to shield the IC which been interfrenced respectively.
4) I recommend to test EMI (CE & RE) to check if it out of standards' spec..

Regards,
Teng

0 Yue TANG over 5 years ago in reply to Teng Feng

TI__Expert 8565 points

Teng,

Thanks for the reply. What is your suggestion to do the ripple test? Is there any material to show how to do the ripple test right.. Actually, They said they did test the ripple before, but no abnormalities were found. I can ask them to do the test again following your suggestion. thanks

0 Teng Feng over 5 years ago in reply to Yue TANG

TI__Genius 13660 points

Hi Yue,

please set Oscilloscope AC coupling and maximum bandwidth to see peak-peak voltage for testing the voltage ripple.

Besides, may you help update another suggestions I proposed.

Teng

0 Teng Feng over 5 years ago in reply to Teng Feng

TI__Genius 13660 points

Hi Yue,

Since We are discussing this issue on email, I will close this thread now. Thanks.

Regards,

Teng

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LM5025A: PMP4468 - EMC Issue