ZHCSH31B August 2017 – February 2018 DRV10987
The ISD function is used to identify the initial condition of the motor. If the function is disabled, the DRV10987 device does not perform the initial speed detect function and treats the motor as if it is stationary.
Phase-to-phase comparators are used to detect the zero crossings of the motor BEMF voltage while it is coasting (motor phase outputs are in the high-impedance state). Figure 18 shows the configuration of the comparators.
If the UW comparator output is lagging the UV comparator by 60°, the motor is spinning forward. If the UW comparator output is leading the UV comparator by 60°, the motor is spinning in reverse.
The motor speed is determined by measuring the time between two rising edges of either of the comparators.
If neither of the comparator outputs toggles for a given amount of time, the condition is defined as stationary. The amount of time can be programmed by setting the register bits ISDThr[1:0].