Part Number:DRV8305
Dear all,
we are intending to use DRV8305 for sensorless 6-step trapezoidal control. We are using evaluation board DRV8305-Q1EVM, connected to an external micro-controller (signals EN_GATE, INHA, INLA, INHB, INLB) in 1-PWM mode with active free-wheeling.
What we observe is a really bad estimation of the zero-crossing events. Minor modifications on the commutation time (around 50 us) cause the zero-crossing time to move with an unexpected 10x factor (around 500 us).
This effect made us think that the BEMF voltage measurement is disturbed by some effect we do not understand. While investigating this, we have observed current flow in the un-powered phase, which might confirm the existence of an undesired voltage component which is masking the real BEMF.
We have configured the device with maximum MOSFET currents, and different dead-time values (that do not have an impact on the observed effect).
Is there any reason why we cannot get good BEMF measurements using the out-of-the-box evaluation board? This effect is currently blocking our project since we cannot use the BEMF to estimate motor position/speed...
- Plot of current in one-phase, along with the 3 GPIOs used to implement 1-PWM mode, the zoom shows the unexpected current in the un-powered phase:
- Plot of phase voltage and current, with zoom in the current when the phase is not powered:
Best regards,