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DRV8434AEVM: Stall Detection Questions

Cherry Zhou
Mastermind 22235 points
Part Number: DRV8434AEVM
Other Parts Discussed in Thread: DRV8889-Q1, DRV8434A

Hi Team,

Using the DRV8434AEVM+TI Official APP to control stepper motors with 1.8° step angle, motor coils--R:4.3ohm, L:3.44mH(f=1kHz)

Now configure Pin20 TRQ_ CNT/STL _TH as torque count output mode:

Determine the status of the motor stall at different speeds, Microstep, Vref by detecting the change in output voltage at that Pin and there're few questions:

1) Pin20 TRQ_ CNT/STL _TH cannot determine motor stall at high microsteps (Microstep > =64x) when the motor speed and Vref do not exceed a certain value. For example, at 200rpm, Vref is 0.99V, at 32x Microstep, the initial voltage of TRQ_ CNT/STL _TH is approximately 1V. The voltage drop is 80mV when the motor is stalling, but when set to 64x Microstep, that Pin is initially about 30mV; and when the motor is stalling, voltage is still 30mV. 

2) The TRQ_ CNT/STL _TH initial voltage trips (1.4V-->2.4V) when the motor speed jumps from 250rpm to 300rpm. For example, 16x Microstep, Vref is 0.99V, initial voltage is approximately 1.6V at 250rpm and initial voltage is approximately 2.4V at 300rpm. However, the initial voltage does not jump significantly when the speed remains below 250rpm. 

3) I_Fs full range current is changed by changing the Vref, and it is found that when Vref is going from 1.32V to 1.65V, the TRQ_ CNT/STL _TH initial voltage has a jump (1.4V--2.4V). For example, 200rpm 16x Microstep 1.32V, initial voltage 1.4V and Vref set to 1.65V, initial voltage changes to 2.4V. However, when Vref is set to 0.99V, 0.66V, the initial voltage does not change so much. 

4) Configuring the TRQ_ CNT/STL _TH in learning mode will not allow the learning process to be completed in some cases (i.e. when the voltage at the TRQ_ CNT/STL _TH output cannot be detected in torque count mode). 

5) In high microsteps (Microstep>=64x), changing the Vref or speed above the threshold (VrefVref >=1.65V or speed >=300rpm), TRQ_ CNT/STL _TH can perform stall detection. For example, at 200rpm, 64x Microstep, Vref=0.99V, the output of the TRQ_ CNT/STL _TH is unable to detect the Stall state. However, after changing the speed to 300rpm or Vref to 1.65V, the TRQ_ CNT/STL _TH can complete stall detection. 

Could you please help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Genius 11580 points

    Hi Cherry,

    These issues will be analyzed in the lab on Monday. I will get back to you as soon as I has results.

    Best,

    David

  • +1 in reply to David Medis
    TI__Mastermind 24285 points

    Hi Cherry,

    Please refer this application note to understand the principle of stall detection, https://www.ti.com/lit/an/slvaei3/slvaei3.pdf. While this report describes the DRV8889-Q1 the principle is the same for DRV8434A except that DRV8434A has higher resolution with torque count equal to 12-bits and also a x8 torque count multiplier to support wider operating conditions.

    Stall detection requires STRC (ripple control decay) mode operation and consistent number of TOFF cycles in the current waveform quadrants. At high microsteps, high step rates and higher target currents the current may not rise fast enough to have enough number of TON and TOFF cycles within each microstep. Depending on these parameters, motor characteristics and supply voltage, at a certain transition step rate torque count calculation for stall detection will not be possible and stall cannot be detected under these conditions. I hope this helps understand this issue. Thanks.

    Regards, Murugavel