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LP8863-Q1: LP8863-Q1_EMC

Part Number: LP8863-Q1

Hi,

We faced some EMC issues while evaluating/testing RE (Radiated Emission) and CE(Conducted Emission).

and it seems it's realted to LED dimming driver (LP8863-Q1) solution.

In addtion to your layout recommendation, is there any other recommendation for this/EMC issue  ??

for example, how to improve/enhance EMC ??  EMC layout guideline of LP8863-Q1.  EMC lesson and learnt (of LP8863-Q1) ...

or do TI/you have any other good advice ??

Thanks a lot

CD

 

  • Hi CD,

    What is the frequency range that the RE/CE test fail? Can you share the test result? And what is your switching frequency? In addition to the layout, some other ways to improve the EMI includes adding the gate drive resistor to slow down the switching speed, or adding input EMI filter.

  • Hi, Shirley :

    Let me describe at the beginning.

    RE03 would be failed (page 6) while setting boost frequency at 300 KHz. Measurement level would be over the limit from 0.614 MHz to 1.524 MHz.

    When boost frequency was setting to 2.2 MHz, RE03 can pass (page 7) the low freqency those failed in setting boost frequency at 300 KHz.

    However,

    CE02 seems quite good (page 3) while setting boost frequency at 300 KHz. and

    CE02 would be failed (page 4 and 5) When boost frequency was setting to 2.2 MHz.

    As for the detail test data, you can refer to the attached file.

    We showed you the LED driver (LP8863-Q1) schematic at the same time (at the first two page).

    Do you have any good idea or any experience on such kind situation  ??

    How about your recommendation  ??

    Thanks

    CDLP8863-Q1_CE-RE pre-scan_0613.pdf 

  • Hi CD,

    Thanks for sending the detailed results.

    For the CE issue at 300kHz switching frequency (page 6), it fails at switching frequency and its harmonics. Enable the spread spectrum can help to mitigate.

    For the other failed frequency range, please add gate resistor from the GD pin to the gate of the external FET. Resistance range around 10-30ohm should be ok. But be noted that the switching loss will be increased. So it's a tradeoff between efficiency and EMI performance.

  • Hi, Shirley :

    No matter we enable spread spectrum or not, we can't pass/lower current limitation so far.

    We knew it would be helpful, especially for those peak (value). so we would like to enable spread spectrum currently.

    As for your second recommendation (add gate resistor from the GD pin to the gate of the external FET),

    In fact, we evaluated it while debugging CE/RE and can't get good result (improve too much) till now.

    Let's think about it further.

    Finally, do you any other recommendation ??

    No matter your lesson learnt or other customer's experiecne or ...  can be provided  ??

    Thanks

    CD

  • Hi CD,

    Firstly, we think the most important thing is the layout. Usually optimizing the layout can improve a lot. If the layout is fixed that can't be optimized, some recommendation includes:

    1. Increasing the gate resistor. If the switching frequency is not high, such as 400kHz, you can try to increase the gate resistance to 30ohm. But be sure to pay attention to the efficiency.

    2. Using a E-shield inductor, such as the IHLE series inductor from Vishay.

    www.vishay.com/.../redemiwihle.pdf

    3. Optimizing the input EMI filter, especially adding a common mode choke.

  • Hi, Shirley :

    Understood, we optimized our layout design now, and our inductor was with E-shield type originally.

    Of course, We hope it could improve EMI result in the near futhre.

    Anyway, thanks a lot for your recommendation.

    Regards

    CD