Quote:
Originally Posted by MPaulHolmes
1. I re-enable pwm in the software automatically after <= 1mS regardless of if current has gotten under control.
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Our controller has software-only overcurrent control, which means we are much more careful about it. (Plus we had two batches of counterfeit IR MOSFETs which caused us to rewrite the limit code a few times.)
We check just before setting the PWM register, and skip the next PWM cycle (set the width to 0) whenever the current is above the limit.
This is a separate, explicit check that is not part the normal control loop. That way changing the control loop constants won't accidentally defeat the current limit.
We hit the current limit frequently, and can tell immediately by the hissing noise from the motor that results.
We also clamp the MOSFET to the live bus bar. We haven't seen any gate drive issues from that configuration, even with one DC-DC converter and a single gate driver driving all of the MOSFETs. It may be because we run a twisted pair from the gate driver board to each MOSFET. The actual connection to the MOSFET pins is made with a tiny (0.5"x0.325") circuit board that has a 10R gate resistor and 1R0 source resistor.
That reminds me, you might consider adding a gate drive LED for debugging.
Our gate connection circuit board has pads for a TVS (SMBJ12A), and a LED+resistor (both 0805 size). The LED is only installed on the end MOSFET board. Even pointed the wrong way, the reflected glow lets us know that the gate driver is working during tests. In retrospect, we should have put LEDs on the gate driver board itself, but they had already been made.