ZHCSH31B August 2017 – February 2018 DRV10987
The start-up current setting is to control the peak start-up current during open loop. During open-loop operation, it is desirable to control the magnitude of drive current applied to the motor. This is helpful in controlling and optimizing the rate of acceleration. The limit takes effect during reverse drive, align, and acceleration.
The start current is set by programming the OpenLCurr[1:0] bits. The current should be selected to allow the motor to reliably accelerate to the handoff threshold. Heavier loads may require a higher current setting, but it should be noted that the rate of acceleration is limited by the acceleration rate (StAccel[2:0], StAccel2[2:0]). If the motor is started with more current than necessary to reliably reach the handoff threshold, it results in higher power consumption.
The start current is controlled based on the relationship shown in Equation 4 and Figure 25. The duty cycle applied to the motor is derived from the calculated value for ULimit and the magnitude of the supply voltage, VCC, as well as the drive state of the motor.