LTC4364 OV triggering early

Hello, 

When trying to Verify our protection circuit using the LTC4364, the overvoltage protection triggers below the 1.25V level on the OV pin.  We have designed for an OV level of around 60V but the device shuts off the HGATE Pin at 51V.  All other protection aspects of the device appear to be working correctly (under voltage, over current).  The schematic is attached below

When the device shuts off the output, the Timer pin toggles with a sawtooth wave up to 1.35V and back as expected.  I have noticed that there is a 1V drop across the 2.2K recommended pullup on the VCC line.  From other posts it looks like this will affect how quickly the Timer pin voltage rises, however the overvoltage pin is still less than 1.25V.  Is there a maximum allowed difference between VCC and Vout, above which the device will disable the output?  If this is the case, how much smaller of a VCC resistor is recommended to still protect the IC?

Thanks,

Andrew



fixed behavior of timer pin
[edited by: andrewlints at 12:51 PM (GMT 0) on 29 Jan 2019]
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  • +1
    •  Analog Employees 
    on Feb 7, 2019 7:04 PM

    Hi Andrew,

    The part is timing out since the output clamp is set to 51 V. LTC4364 is designed to regulate 1.25V at FB pin for the time set by the timer capacitor.

    As you increase the input above the clamp voltage set by external feedback resistors, the timer runs , and HGATE is regulated for the time set by the timer capacitor, and then shuts off the MOSFET. This is normal behavior.Since LTC4364 is is surge stopper , it does not shut-off due to OV , it just inhibits startup and auto-retry during input OV.  

    Let us know if you have any further questions. 

    Best Regards,
    Ritesh

Reply
  • +1
    •  Analog Employees 
    on Feb 7, 2019 7:04 PM

    Hi Andrew,

    The part is timing out since the output clamp is set to 51 V. LTC4364 is designed to regulate 1.25V at FB pin for the time set by the timer capacitor.

    As you increase the input above the clamp voltage set by external feedback resistors, the timer runs , and HGATE is regulated for the time set by the timer capacitor, and then shuts off the MOSFET. This is normal behavior.Since LTC4364 is is surge stopper , it does not shut-off due to OV , it just inhibits startup and auto-retry during input OV.  

    Let us know if you have any further questions. 

    Best Regards,
    Ritesh

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