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ISOW7841: Over-voltage protection
Part Number: ISOW7841
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
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In reply to Manuel Chavez:
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.
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
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
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!
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
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.
Hi Goran,This is good to hear! Please allow me to follow up via Personal Message.Thank you for your time,Manuel Chavez
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