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I am creating an ESC for a BLDC motor. Here is my schematic:

enter image description here

I'm still in the testing stage to make the motor spin with this ESC and while I'm testing, somehow the FAN7392N ICs always break and I have no idea why.

I hooked my circuit up to an LED with a resistor in series and everything worked fine the way I wanted it to. Then I hooked my circuit up to my motor instead of the LED and resistor and suddenly the motor doesn't work.

Then when I try to go back to the LED and resistor to see what's wrong suddenly the LED doesn't work either. Then if I switch out the FAN7392N IC with a brand new FAN7392N IC the LED will start working the way I want it to. So obviously somehow the motor is breaking these ICs.

I've gone through about 6 of these chips now and I don't understand why they keep breaking because I have it hooked up exactly like they recommend in the datasheet.

While testing the motor there were about 2 or 3 times when I had both the upper and lower MOSFET "ON" at the same time which caused a short circuit between the source of the upper MOSFET and drain of the lower MOSFET but it was for less than a few milliseconds. This caused about 7 A to flow through the source/drain for a short period of time.

This short circuit is the only thing that I can think of which could have potentially damaged it, but even then would a short circuit affect the FAN7392N IC since the IC is hooked up to the gate of the MOSFET, not the source/drain?

Despite this short circuit the motor will be running at about 50 A max. so if these ICs can't even handle 7 A running through the drain/source then I've got a problem because I need 50 A flowing through it.

Does anyone have any recommendations so I don't keep breaking these ICs?

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  • \$\begingroup\$ Also just realizing this now, but I accidentally connected the Vs pin to the Gate of upper mosfet in my circuit diagram, but this was a mistake. Ignore that, the Vs pin should be connected between the source / drain of the upper and lower mosfet, not the gate. \$\endgroup\$
    – Trev347
    Commented Sep 23, 2022 at 22:48
  • \$\begingroup\$ What is the Vcc in your circuit? \$\endgroup\$
    – Math Keeps Me Busy
    Commented Sep 23, 2022 at 23:02
  • \$\begingroup\$ While I was testing its 15V, but when I put my real battery it will be 36V \$\endgroup\$
    – Trev347
    Commented Sep 23, 2022 at 23:02
  • \$\begingroup\$ figure 1 diagram is different from your diagram \$\endgroup\$
    – jsotola
    Commented Sep 23, 2022 at 23:09
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    \$\begingroup\$ First, make the circuit diagram complete and accurate. If the circuit is wired this way it will not work. The 1N4007 will not work. The data sheet indicates the diodes that you should use. Put decoupling caps from VDD to Vss. If you are breadboarding, still follow the placement guidelines on page 15 of the datasheet the best that you can. The inductive load will take out the chips if you don't follow good layout. Short wires and minimize the area of current loops is imperative. \$\endgroup\$
    – user319836
    Commented Sep 23, 2022 at 23:57

2 Answers 2

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There are multiple mistakes in the schematic you provided. As you said, you forgot to connect HO to the gate of your high side FET for phase 1 and have incorrectly connected the gate instead to Vs. In phase 2, you forgot to connect Vs, and have incorrectly connected the bootstrap diode. In all three phases, COM needs to be connected to ground for the high side switching to function properly, which you have not done.

Also, I do not see bypass capacitors anywhere in the provided circuit. Your circuit will not survive an attempt to commute a BLDC motor running at 50A 36V with 0 bypass capacitors.

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The back emf is killing your fets. you need to have 'freewheel' diodes in there to direct the generated back EMF. look at more schematics of h-bridges, there will be a diode in parralell with each transistor. The Body diode of the FET is not suitable to take the place of a freewheeling diode.

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  • \$\begingroup\$ I also added fly back diodes after destroying the first 3, and that didn't seem to help because even with them I destroyed the other 3. \$\endgroup\$
    – Trev347
    Commented Sep 23, 2022 at 23:36
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    \$\begingroup\$ Power MOSFETs include an intrinsic body diode that is rated at least as much, reverse, as forward drain current. This part is rated 557A. See: infineon.com/dgdl/… \$\endgroup\$
    – Tim Williams
    Commented Sep 24, 2022 at 0:47

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