SLVSC40H June 2013 – May 2020 DRV8711
PRODUCTION DATA.
To use an external microcontroller to manage stall detection, the EXSTALL bit in the CTRL register is set to 1. In this mode, the STALLn / BEMFVn output pin is used to signal a valid back EMF measurement is ready. In addition, the SDT and SDTLAT bits are also set at this time.
BEMFVn and BEMF are still valid outputs in this mode even if the step time is smaller than SMPLTH time.
When the BEMFVn pin goes active low, it is an indication that a valid back EMF voltage measurement is available. This signal could be used, for example, to trigger an interrupt on a microcontroller. The microcontroller can then sample the voltage present (using an A/D converter) on the BEMF pin.
After sampling the back EMF voltage, the microcontroller writes a 0 to the SDTLAT bit to clear the SDT bit and BEMFVn pin, in preparation for the next back EMF sample. If the SDTLAT bit is not cleared by the microcontroller, it will automatically be cleared in the next zero-current step.
For either internal or external stall detection, at very high motor speeds when the PWM duty cycle approaches 100%, the inductance of the motor and the short duration of each step may cause the time required for current recirculation to exceed the step time. In this case, back EMF will not be correctly sampled, and stall detection cannot function. This condition occurs most at high degrees of micro-stepping, because the zero current step lasts for a shorter duration. It is advisable to run the motor at lower degrees of micro-stepping at higher speeds to allow time for current recirculation if stall detection is needed in this condition.