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ISOW7841: using with ADS131A04 to isolate SPI lines from noise wireless module

Mahesh Hooli
Intellectual 740 points
Part Number: ISOW7841
Other Parts Discussed in Thread: ADS131A04, , ISO7741

Hello Team ,

We need to keep noise low at the ADC (ADS131A04)  end so thinking of isolating the digital lines (SPI) connecting from ADC to Wireless module. For power, we use only LDOs to avoid switching noise.

The part ISOW7841 has built in DC-DC and we are worried of switching noise. Wondering if we can use this device for digital isolation in our design. Can we leave its secondary power (near ADC) unconnected ?.

The analog inputs to ADC are at 65uV. Please suggest on digital isolation requirements ?

Thanks

Mahehs

  • 0
    TI__Mastermind 49445 points
    Hi Mahesh,

    Could you please confirm if you are powering ADS121A04 with ISOW7841 or are you powering Wireless Module with ISOW7841? Can you please share us with your noise / ISOW output ripple requirements?

    Regarding your question on leaving secondary power (VISO of ISOW7841) unconnected, yes it is not mandatory to have load on VISO. VISO powers ISOW7841's internal circuitry on secondary side.

    If you already have power available for ADC / Wireless Module and not using VISO of ISOW7841, then you could also think of use a digital isolator without DC-DC integrated in place of ISOW7841. ISO7741 could be a suitable device. Please correct me if my understanding about your application and device usage is incorrect. Thanks.


    Regards,
    Koteshwar Rao
  • 0 in reply to Koteshwar Rao
    Intellectual 740 points
    Thank you Koteshwar for suggesting the part. ISO7741 might for work for us. We won't be using power isolation through transformer so we will be connecting GND1 and GND2 of ISO7741. hope this is fine ?
    We are powering ADC through LDO (battery powered). We are aiming for 22 bit ENOB (with 5V). Please let me know if you have any questions.
  • 0 in reply to Mahesh Hooli
    TI__Mastermind 49445 points
    Hi Mahesh,

    I am still unclear about power and signal connections between isolator, ADC & Wireless Module. Is it possible for you to share either a block diagram or schematic of your system so that I can better comment which device is suitable and how much does it impact your system design. Let me know, thanks.

    Regards,
    Koteshwar Rao
  • 0 in reply to Koteshwar Rao
    Intellectual 740 points

    Hi Koteshwar,

    I have added the block diagram below.

    WiFi module and Isolator shares same 3.3V supply

    ADC has its own 3.3V LDO

    But we are not separating the ground.  Please provide your suggestion. Thank you.

    Mahesh

  • 0 in reply to Mahesh Hooli
    TI__Expert 6195 points
    Hi Mahesh,

    I see that there has not been any communication in this thread for a few weeks. If this issue is not resolved, please reply to this thread or start a new one and we will be happy to further assist you. Otherwise, I am going to assume that you were able to resolve this issue.

    Best regards,
    Dan