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ISOW7841: ISO7841 EMI TEST Fail

chunqiu lv
Intellectual 715 points
Part Number: ISOW7841
Other Parts Discussed in Thread: ISO7841

Dear TI team:

Customer have a Ecg Project use ISO7841 ,Now there's a problem that you need to suggest.

We use creepage distance method to isolate the input and output（Similar to AC power Primary and secondary isolation）. The distance between the input and output is 8mm，this way test emi Fail ,Fail frequency  at 240MHZ

according to the reference design layout, test OK. But there is only FR-4 material isolation between the input and output . Customer are worried that we can not get the isolation

voltage standard, so we need a better solution

 

  • 0
    TI__Mastermind 49445 points

    Hi Chunqiu,

    Thank you for reaching out to us regarding customer EMI issue. I understand customer's concern in using inter-layer stitching capacitor where the insulating material is going to be FR4 material.

    If you can share customer emissions test results then I will be able to better understand how much is the fail and how much improvement is required. Please do share the below details to help you better.

    1. What is input supply voltage, VCC? Output supply VISO? Max output current requirement?
    2. What is the emissions standard does customer need to meet? CISPR 2 Class A? Please share emissions test results also.
    3. If possible, please do share emissions test setup picture. Any cables or electrodes connected to customer PCB will also largely impact emissions results.
    4. If customer is not comfortable sharing all this information in this E2E post, then please let me know I can send you an email.

    Stitching capacitor is important to reduce radiated emissions but if the failure is only happening at a small band of frequencies then emissions can be reduced by using suitable common-mode chokes (CMC) on input and output supplies as shown in the image below.

    If customer emissions are only failing at 240MHz then customer should choose CMCs with impedance >>1kΩ @ 240MHz. In addition, it is also recommended to have >1kΩ resistance in series to all I/O pins. This should help reduce emissions at 240MHz. Let me know if you have any questions, thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Intellectual 715 points

    Dear Koteshwar Rao :

    Thank you for your reply，

    1.What is input supply voltage, VCC? Output supply VISO? Max output current requirement?

    input 3.3V ,output3.3V, output current 10mA

    2.What is the emissions standard does customer need to meet? CISPR 2 Class A? Please share emissions test results also.

    emissions standard :CISPR 2 ClassB,The actual test class A  failed

    3.If possible, please do share emissions test setup picture. Any cables or electrodes connected to customer PCB will also largely impact emissions results.

    We are now excluding the influence of other factors, only retain your chip and its peripherals can not pass. You can provide a DEMO board that you think can pass EMI to test

    4.If customer is not comfortable sharing all this information in this E2E post, then please let me know I can send you an email.

    Customer email:zlbeck@126.com  web: www.blt.com.cn 

  • 0 in reply to chunqiu lv
    TI__Mastermind 49445 points

    Hi Chunqiu,

    Thank you for sharing the requested information. I will write to you on your email requesting further information. Thanks.

    Regards,
    Koteshwar Rao