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StealthChop2 Autotuning not working

Category: Hardware
Product Number: TMC5240

Currently I am developing new electroncis for one of our products using TMC5240 motor drivers. As recommended by the reference manual for StealthChop2, I want to determine the motor specific parameters for PWM_GRAD and PWM_OFS with the TMC5240-EVAL board and TMCL-IDE (version 4.3.0).

The motor parameters are:

Phase resistance: 40Ohm

Phase inductance: 23mH

Motor max. current: 0.32A

Holding torque: 0.18Nm

The TMC5240 operating conditions/settings are:

Supply voltage: 24V

Reference resistor: 48K

IRUN: 24 (0.14A)

IHOLD: 24 (0.14A)

PWM_REG: 4 (default)

PWM_FREQ: 0 (default)

As recommended for AT#1 step, I set IRUN and IHOLD identical and enabled StealthChop with both PWM_AUTOSCALE and PWM_AUTOGRAD enabled. I see PWM_OFS_AUTO = 238 and PWM_SCALE_SUM = 740 in the register browse after a short delay.

Afterwards I moved the motor for AT#2, but unfortunately it does not succeed. For example with a velocity of 60RPM, I get:

PWM_SCALE_SUM = 957

PWM_SCALE_AUTO = 52

PWM_GRAD_AUTO = 0

With 30RPM, I get:

PWM_SCALE_SUM = 809

PWM_SCALE_AUTO = 15

PWM_GRAD_AUTO = 0

I tried this step with different velocities, but I cannot fulfill the conditions given in the manual. PWM_GRAD_AUTO always remains zero and PWM_SCALE_AUTO does not regulate to zero.

Am I doing something wrong or is my motor exceeding the limits of StealthChop2?