Currently have 3 TMC9660 boards, all exhibiting the same behavior. I set them up in UBLTools and TMCL-IDE using the default parameters specified in the datasheet for a 3-phase BLDC motor. I used the Wizard to test the TMC9660 configuration process before writing application code. Up to this point, there were no problems. However, once it was time to start the system, all phases had their bootstrap undervoltage flags go up, even Y2, which is unused. Clearing these bits was pretty easy (except for Y2, for which the protection flag needed to be disabled again, even though it was already disabled, to clear the flag). This seems to happen every time I first switch to open-loop mode. Once in open-loop mode, power was immediately being consumed, despite being at 0 duty cycle. The amount of power lost through shoot-through did not change with the duty cycle; it scaled with voltage. Upon checking with an oscilloscope, shoot-through occurs on every phase.
I tried every combination of adaptive drive time on/off, the break before make time, gate drive current, etc., and nothing affected how much shootthrough was occurring. All three units have the same exact problem.
The only setting that affected shoot-through was setting the switching scheme to flat bottom, which reduced it by 20%.
This power loss is present in all modes available to me: open-loop current, voltage, and Hall-effect. In system off, but with the Low-side or High-side fets set to high, there is no power loss.
To summarize, I'm facing these problems:
- Unknown undervoltage bootstrap warning on startup and first initiation of the gate drive unit.
- Shootthrough that is not affected by any parameter setting except switching scheme type, and is present in all modes.
Attached is an image of the schematic.
I'd appreciate any help. Thank you.
