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TPS54340: Not qualify EMI/EMC - CISPR25 Radiated Emission

Joice J Paliyath
Prodigy 20 points
Part Number: TPS54340

Dear Sir,

We are facing Radiated Emission test failure issue due to the TPS54340BQDDAQ1, that radiated emissions above the limits at 74.15Mhz , 75Mhz and 171.6Mhz frequencies. Could you please suggest solutions to reduce the radiated emissions? I have attached the test results and schematics of the power supply side.

Horizontal Results

Frequency

Avg

Limit

Margin

dBuV/m

dBuV/m

dB

41.4

41.98

49.467

7.49

74.15

43.06

42.189

-0.87

75

43.01

42

-1.01

100.05

40.00

42.848

2.85

146.55

43.85

44.422

0.58

171.6

45.77

45.269

-0.50

217.1

29.28

46.809

17.53

286.8

33.81

49.168

15.36

348

31.40

51.24

19.84

429.85

10.89

53

42.11

521.16

13.46

53

39.54

600.31

13.15

53

39.85

884.23

12.49

53

40.51

Thanks and Regards

Joice J Paliyath

  • 0
    TI__Genius 11085 points
    The radiated EMI performace of a buck is highly related to the PCB layout. A few things you can try before redo the layout.

    You can add a small HF ceramic bypass cap (.1uF to .47uF) as close as possible between the VIN pin and the ground pad of D11.

    You can add a snubber circuit from SW node to ground.

    You can also add a small bypass cap (1uF) between Vout to ground.

    The most effective way is to add a pi filter at the input port. It will improve both conducted and radiated emission.

    -Yang
  • 0 in reply to YangZhang
    Prodigy 20 points
    Dear Yang,

    Thank you for your suggestions.

    I will test it and revert back to you.

    Thanks and Regards
    Joice J Paliyath