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Original question:

ISOW7841EVM: ISOW7841EVM

ISOW7841: EM radiated emission Failure

Pedro Mietto83
Prodigy 130 points
Part Number: ISOW7841
Other Parts Discussed in Thread: ADS124S08

Hello,

We are developing a board with the ISOW7841 that supplies two ADS124S08, and we are facing failure on radiated emission testing, as we can see below:

Our equipment has the following configuration / requirements:

  • Medical equipment that must be in compliance to 60601
  • Input Voltage = Output Voltage = 3.3V
  • Maximum load = 100mA
  • 4kVac Hipot isolation requirement

There are 6 cables of 3m length connected to the ADCs; 3 cables on each ADC.

When we unplug all cables, the emissions fall below the limit.

Could you review our current design and provide some modifications to improve these results? We can share board schematic and layout on email.

Best regards.

  • 0
    TI__Mastermind 49535 points

    Hi Pedro,

    Thanks for sharing this information and sorry to hear about the emissions issue.

    Please do note that ISOW can only support a max current of 75mA when VCC = VISO = 3.3V. I see you have stated that your max current can be upto 100mA, we do not recommend drawing any more current than 75mA.

    Thanks for testing ISOW for emissions without the cables and sharing the information. Yes, the cables along big PCB sizes do contribute to worsen overall system level emissions. Please do follow the recommendation of using CMC for power rails and FB/resistors for data lines as stated in the below E2E.

    Implementing the above suggestions should definitely improve the emissions and enable you to meet your emissions requirements. Could you please confirm if your requirement is to meet CISPR 11 Class A or Class B?

    I will reach out to you over email requesting for schematic and PCB layout for review. Thanks.

    Regards,
    Koteshwar Rao