This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

  • Resolved

ISOW7841: Overvoltage protection for ISOW7841

Prodigy 225 points

Replies: 9

Views: 253

Part Number: ISOW7841

Hi Koteshwar,

We have build the board with several ISOW7841 + overvoltage protection circuit as per SLLA440 and revised resistor values from our previous correspondence. Unfortunately, none of ISOW7841s turns on - it seems that PFET is preventing it (when PFET is removed, the output voltage is fine).

I have attached my schematic - could you please have a look and advise!?

Thanks,

Goran320879-B 11_RS422-3 Interface-Isolated.pdf

  • Hi Goran,

    I am Manuel Chavez, a colleague of Koteshwar's. Gate capacitance of PMV30XPEA might be too high for TLV3012 to drive, so the P-FET may be continuously shorting +3V3-ISO3 to 0V-ISO3. Can you attempt to use DMP3056L instead?


    Thank you,
    Manuel Chavez

  • In reply to Manuel Chavez:

    Hi Manuel,

    Thank you very much for your prompt reply - I'll try DMP3056L (it will take few days to get it in).

    My only concern is that DMP3056L has much higher gate-source threshold voltage than PMV30XPEA, so UVTP might need to be increased as well - I'll let you know the outcome.

    Thanks,

    Goran

  • In reply to Gorbal:

    Hi Goran,

    No problem! Thank you for anticipating the request and placing an order for DMP3056L.

    Before modifying UVTP levels, can you re-attempt tests of PMV30XPEA with the drain and source pins switched? I had not realized earlier, but this component might be connected incorrectly.

    I look forward to your response.


    Best,
    Manuel Chavez

  • In reply to Manuel Chavez:

    Hi Goran,

    Hopefully all is well. Please let us know if switching the drain and source pins of the P-FET as mentioned above allowed the ISOW7841s in this circuit to power on.


    Have a great weekend!

    Manuel Chavez

  • In reply to Manuel Chavez:

    Thanks Manuel!

    Sure will do - the reason I have been quiet was that I had some urgent things to do on other projects - I hope I'll get back to this one mid-week and will let you know how it goes. Having said that (and looking again at the AN and my drawings), I am quite sure that the swapping drain and source pins will solve it - sometimes the most obvious errors are easily missed :-(.

    I'll be in touch as soon as I get some results!

    Best regards,

    Goran

  • In reply to Gorbal:

    Hi Goran,

    No worries! I apologize for initially missing this.. I'm glad we've found a possible solution and look forward to hearing back from you :)


    Respectfully,
    Manuel Chavez

  • In reply to Manuel Chavez:

    Hi Manuel,

    We've managed to get back on this project late last week.

    We have tested the circuit (without ISOW7841) with swapped drain and source pin and different P-MOSFET (Rohm, RQ5C035BCTCL) and it behaves as expected at OVTP=3.7V.

    We can't see any issue when testing full circuit (with ISOW7841) and it is very hard to detect whether ISOW7841 goes out of regulation at all - we will do more testing, of course, but it would help if you are aware of easy way to induce ISOW7841 into unregulated mode, so we can see that P-MOSFET kicks back in as expected when the voltage drops under UVTP=1.9V.

    Best Regards,

    Goran

  • In reply to Gorbal:

    Hi Goran,

    This is good to hear! Please allow me to follow up via Personal Message.


    Thank you for your time,
    Manuel Chavez

  • In reply to Manuel Chavez:

    Thanks Manuel!

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.