Issue with dual ADM1278 connection.

Hi Experts,

I have a issue with the design dual ADM1278 hot swap controller connection as picture below:

The issue is in the case when PSU1 is delivering power to 12V_main and PSU2 doesn't provide power to 12V_main but at the PSU2 side, we measured a unexpected voltage 12V and a fault event (FET health) in HSC2. After debugging, we found that there is a current from 12V_main to PSU2 via body diode at MOSFET Q2.

Could you please explain why HSC2 notificate FET health? and could you suggest the way connection for dual HSC to avoid the current unexpected in that case?

Thank you so much

Tuan Le

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    •  Analog Employees 
    on Nov 11, 2020 6:19 PM 5 months ago

    Hi Tuan,

        You have correctly observed that when you reverse the drain-to-source bias on FET Q2 the body diode forward biases and conducts current "backwards" from output to input. This is normal behavior. The best way to avoid it is to place two FETs in series in a back-to-back configuration so that when the FETs are off (Vgs = 0) one body diode will always be reverse-biased and no current will flow (actually, there will be some small amount of leakage current).

        Note that the ADM1278 is not the same as an ideal diode (like LTC4412) or prioritizer (LTC4229, LTC4236). You are using the ADM1278 in a way that was not intended, and may or may not be suitable. You can try disabling FET HEALTH checking in the ADM1278's DEVICE_CONFIG[11] register and test the circuit to see if it performs acceptably.

        Check the following article for more information and product ideas that may be more appropriate to what you are doing.

    https://www.analog.com/media/en/news-marketing-collateral/solutions-bulletins-brochures/idp-web.pdf

    Thanks!
      Nathan

  • Hi Nathan,

    Could you please send a document or guideline to guide for disable FET HEALTH function in the ADM1278's DEVICE_CONFIG[11] register? Because my team said that they tried but they can't disable this function?

    Thanks

    Tuan Le

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