Author: Murugavel Raju
Stepper motor drivers such as the DRV8434 family have integrated H-Bridge drivers for each of the two phases A and B of the stepper motor. The Excel calculator tool “Integrated Stepper Driver Thermal Estimator.xlsx” provided in this FAQ, combines all the formulae provided in the Thermal Application section of the device datasheet and automated the calculation. For example, refer DRV8434 datasheet https://www.ti.com/lit/ds/symlink/drv8434.pdf, “Thermal Application” section. Please note this is an estimator tool. The real-world results may vary according to the free air to the PCB radiating surface thermal resistance.
- TOFF can either be fixed TOFF values while in decay modes other than Smart Tune Ripple Control STRC mode. For STRC mode TOFF can be measure using an oscilloscope. Else using Smart Tune Dynamic Decay STDD mode TOFF value in its highest setting could get closer results.
- Back emf amplitude can either be measure by spinning the motor using another motor couple to it and running it at the target velocity or can be estimated using this formula. approximate_back_emf_amplitude = sqrt(2) x pi x rated_holding_torque x revs_per_second / rated_current
Note: This formula requires the holding torque value is specified with both phases energised with the rated current. If the holding torque value is specified with only one phase energized use this formula.
approximate_back_emf_amplitude = 2 x pi x rated_holding_torque x revs_per_second / rated_current
