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EVAL6482 TCC and IGATE parameters

Question asked by Fournier.Peter.001 on May 20, 2013
Latest reply on May 24, 2013 by Enrico Poli
Let me set you up on my situation before I ask my question.

I am experimenting with an EVAL6482 with my design.  I am trying to reach 2900 steps/sec with my mechanical hardware.  I manage to get to 2200 steps/sec without a real problem.  The next jump to  2900 causes it to run then stall.  One of my thoughts was that the MOSFETS were not on long enough to reach the current.  So I tried adjusting TCC in GATECFG1 register.  I thought increasing the value would keep the gate drive on for longer.  Interestingly there seemed to be little to no effect UNLESS I brought the TCC value down to 0 or 1, 125nS or 250nS.  At those levels the 6482 tripped the OCD!  This was totally unexpected,  I figured it would just not run.  To get to TCC=2 I had to turn the TVAL_RUN and TVAL_ACC vary low.  I increased TCC all the way to the maximum and nothing noteworthy happened.  I finally put a scope on one of the gates and found that the gate voltage width was ALWAYS 684 uS no matter what I set TCC to.  Am I looking at the wrong thing here?

BTW, I originally chose IGATE of 96mA and TCC of 625nS because gate charge is 55nC and those were 2 settings that got me at least 55nC.  If I had chosen a lower current I would have had to choose a longer TCC.