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LM5069: LM 5069 -Mosfet not turn ON , hysteresis too long during recovery

vikas salvi
Prodigy 170 points
Part Number: LM5069


Hello  , 

We are using LM5069 circuit for OVP protection and reverse polarity  as per application note SNVA683 , Please find below snap 

We observed that, LM5069 not providing gate signal to the MosFET to turn ON.

But whenever we probe at test point TP 19 shown in above schematics then it starts functioning and Mosfets getting ON. 

 Also, we have observed that hysteresis is very high than the calculated recovery voltage during recovery after OVP.

please help to know the root cause.

Thank you ,

Vikas

8182.Presentation1.pdf

  • 0
    TI__Guru** 106191 points

    Hi Vikas,

    Thanks for reaching out.

    D1 in the ground path will shift the OVP threshold. Can you please short the D1 and test.

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Prodigy 170 points

    Hi Rakesh,

    thanks for your feedback. yes, i agree diode D1 in GND path will shift the OVP threshold. The OVP cut off happens correctly as expected but recovery is taking too much hysteresis around 7~ 8 V. Why is it so?

    Another important issue is LM5069 not providing any gate signal to Mosfet  even when Input voltage in normal operation range but switch ON when we touch (by Multimeter probe) at OVP pin or at TP 19 as shown in schematics.  This is really strange, and we could not be able to produce any further parts. 

    We cannot remove the diode D1 as we need RVP.

    please guide us as it is really very much concerning to us.

    thank you .

    Vikas 

       

  • 0 in reply to vikas salvi
    TI__Guru** 106191 points

    Hi Vikas,

    Can you quickly confirm.

    • Are the OVP cut-off thresholds fine without D1? If not - can you share test waveform of Vin, Vout, GATE and OVP voltages
    • Is GATE signal coming up without any sensitivity issue when you short D1 ?

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Prodigy 170 points

    Hello Rakesh, 

    1) Yes, the OVP cut off thresholds are fine as required without Diode D1.

    2) Yes, gate signal coming fine without diode, without any sensitivity issue on same board.

    What could be the reason? please guide us as we cannot remove the diode D1 from circuitry  

    thank you,'

    Vikas 

  • 0 in reply to vikas salvi
    TI__Guru** 106191 points

    Hi Vikas,

    Thanks for the confirmation!

    The multimeter impedance might be affecting the OVP pin node. Please use high impedance 10 MΩ probes for measurement and check.

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Prodigy 170 points

    Hello Rakesh,

    the main problem is why LM5069 not working with Diode D1 or having wide voltage Recovery. 

    please let us know your feedback 

     Thank you  ,

    Vikas 

  • 0 in reply to vikas salvi
    TI__Guru** 106191 points

    Hi Vikas,

    Can you share

    1. Diode D1 part number
    2. Test waveform of Vin, Vout, GATE and OVP pin during recovery. Please use high impedance 10 MΩ probes
    3. What additional circuits are there on your system board
    4. layout of LM5069 design

    Best Regards,

    Rakesh