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ISOW1412: 54MHZ noise pulses of 568mV embedded in the A and B signal lines for both HIGH and LOW signals

lance Forman
Intellectual 280 points
Part Number: ISOW1412

Tool/software:

I am using the ISOW1412BDFMR

I am getting a ripple voltage on the A and B output line of  mV. (see picture below)

I am trying to understand what the cause of this 54MHZ noise of around 568mV on the A and B 485 signal lines

Currently there is nothing else connected to these lines as I was transmitting a character.

On the low driven side it has pulses of the 54MHZ noise

I am trying to understand the cause of this noise and if it could be eliminated

 

  • +1
    TI__Guru 54675 points

    Hi Iance,

    Thank you for reaching out.

    As you may already know, ISOW1412 integrates isolated DC/DC converter in the same package including the transformer. To achieve such integration, the DC/DC needs to switch at a high frequency of 25MHz and the noise that you are observing should be a harmonic of this switching noise.

    If the power supply output VISOOUT is filtered out appropriately, we shouldn't see such noise on A/B lines, at least not as much. Could you please share the schematic and PCB layout of ISOW1412 so that I can review to see if the design looks good and if the datasheet guidelines are followed?


    Regards,
    Koteshwar Rao