为何无论我将TCC设置为什么，栅极电压宽度总是为684 uS？

在我提出问题之前，让我告诉你我的情况。


我正在用我的设计试验EVAL6482。我试图用我的机械硬件达到2900步/秒。我设法达到2200步/秒而没有真正的问题。下一次跳转到2900会使其运行然后失速。我的一个想法是，MOSFET的长度不足以达到电流。所以我尝试在GATECFG1寄存器中调整TCC。我认为增加该值会使栅极驱动保持更长时间。有趣的是，似乎几乎没有效果，除非我将TCC值降低到0或1,125nS或250nS。在那些级别，6482绊倒了强迫症！这完全出乎意料，我认为它不会运行。要达到TCC = 2，我必须将TVAL_RUN和TVAL_ACC变低。我将TCC一直增加到最大值并且没有任何值得注意的事情发生。我终于在其中一个门上放了一个示波器，发现无论我将TCC设置为什么，栅极电压宽度总是为684 uS。我在这看错了吗？

顺便说一句，我最初选择的是96mA的IGATE和625nS的TCC，因为栅极电荷是55nC，这两个设置让我至少55nC。如果我选择了较低的电流，我将不得不选择更长的TCC。
＃l6482



以下为原文




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.   
#l6482