Post Go back to editing

LT4363 - Back-EMF voltage protection

Category: Choose a category
Product Number: LT4363CDE-2

The LT4363 Data Sheet shows a circuit for reverse INPUT voltage protection, using two back-to-back NFETs in a common-drain configuration. We have a large inductive load that can generate back-EMF up to 70V, our input voltage is 48V. The reverse INPUT voltage protection circuit does not work in our case, as it is the load generating back-EMF, not reverse voltage on the input. We believe that if we just connect the two NFETs in a common-source configuration, use a 10-Ohm resistor in series with each gate to prevent oscillation, then the LT4363 will generate the same Vgs for both NFETs, turning them on and off at the same time, and the body diodes will be opposite each other, so voltage cannot flow from input to load or load to input unless the LT4363 enables the NFETs. Is this a reasonable design?

I realize that this proposal is just an implementation of a bidirectional switch, using the LT4363 as a NFET controller. We are using the LT4363 because we need to turn this DC path ON and OFF, it will detect when the output voltage is higher than the input voltage, or more correctly, higher than the feedback pin programmed voltage, and it will detect when there is over current.

Added additional information.
[edited by: daveboston at 7:52 PM (GMT -4) on 6 Oct 2022]
  • Hi Dave,
    Check out the LTC4364.
    It has ideal diode functionality, so when when OUT>IN, the "diode FET" will turn off.


  • We already use the LT4363 in several circuits and were hoping to use two NFETs in a common source configuration to act like a bidirectional switch, not change over to the LT4364. We know that the LTC7000 data sheet shows such a connection example and thought the LT4363 would also work the same. It is a simple implementation and we just wanted to understand if there were any obvious/subtle reasons why the LT4363 would not be able to be used in this configuration? We would add separate 10-ohm gate resistors to both NFETs.

    LTC7000 Data Sheet Example