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ISOW7721: using isolator for only digital signals (no load)

NORM NOVOTNEY
Prodigy 30 points
Part Number: ISOW7721
Other Parts Discussed in Thread: ISOM8710,

Tool/software:

What changes/simplification can be mad if the isolated side does not power anything (only provide the isolated logic signals.  We do not want o power anything , ut we cannot use any power form the isolated side circuitry (hence isolator needs internal power).  Our data rate is more like 1-2MHz.  Is there a simpler part or simpler  hookup (such as not requiring ferrite beads?)

  • 0
    Guru 317250 points

    Digital isolators have active circuits on both sides, so they need power on both sides. Even when you do not have another load in addition to the isolated receivers and the logic outputs, you cannot avoid running the DC/DC. A lower load results in less noise, but all switching supplies require some filtering.

    Opto-emulators (and the optocouplers they replace) would need power only on the output side; their inputs are powered from the input signal. But the ISOM8710 has only a single channel.

    If your data rate were below 10 kHz, then you would be able to use a phototransistor optocoupler as a simple switch.

  • 0
    TI__Guru 55815 points

    Hi Norm,

    If I understand your question correctly, you would like to use ISOW7721 to isolate digital signals and you do not like to add any additional load on VISOOUT pin. I am assuming that you do not have any concerns in connecting VISOOUT to VISOIN.

    If this is the case, then yes, this is perfectly normal use case. The DC/DC converter in ISOW7721 is primarily to power the internal circuit and optionally support additional external load. If there is no external load, then that is not a problem. The device will operate normal without any issues.

    If my understanding of your question is incorrect, please do correct me and rephrase your question. Thanks.


    Regards,
    Koteshwar Rao