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LM5574/LM5574-Q1 break "isolation"

Hello

        According to your experience is it possible internally for any reason or a failure to connect the input with the output?  The component is used  to create 12V from 48V.  Is it possible internally to put the MOSFET in short or impendent circuit and to connect the input with output 

sincerely

Panagiotis

  • Hello Panagiotis,

    As far as I know, in normal operation, it is not possible to force this IC to keep the MOSFET on all the time. There is time needed to re-charge the bootstrap circuit every switching cycle and also to sample and hold the catch diode current level. So every cycle there is a forced off-time imposed on the MOSFET.

    If the MOSFET fails short for some reason (e.g. due to EOS), you could have a path from VIN to VOUT (with the inductor sitting in between). I am not sure how you can induce such failure in your 48V to 12V system.

    What are you trying to do?

    Regards,
    Denislav
  • This part has a forced off time to recharge the high side drive and sense the low side current for emulated current mode operation.

    Page 12 of the datasheet described the min off time and max duty cycle.

    'Maximum Duty Cycle / Input Drop-out Voltage There is a forced off-time of 500ns implemented each cycle to ensure sufficient time for the diode current to be sampled. This forced off-time limits the maximum duty cycle of the buck switch. The maximum duty cycle will vary with the operating frequency. DMAX = 1 - Fs x 500ns'

    It cannot provide 100% duty cycle to short Vout to Vin.

    Regards,

    Yang