SLLA663 March   2025 MCF8315A , MCF8315C , MCF8315C-Q1 , MCF8315D , MCF8316A , MCF8316C-Q1 , MCF8316D , MCF8329A , MCT8315A , MCT8316A , MCT8329A

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2End Application Configuration Recommendation
    1. 2.1 Resynchronization
    2. 2.2 Reverse Drive
    3. 2.3 Coasting (Hi-Z)
    4. 2.4 Startup Brake
    5. 2.5 Direction Change Mode
  6. 3Tuning Guidance
    1. 3.1 Initial Speed Detection Module
      1. 3.1.1 Initial Speed Detection
      2. 3.1.2 ISD Times
      3. 3.1.3 Stationary Detect Threshold
    2. 3.2 Resynchronization
      1. 3.2.1 Forward Drive Resync Threshold
      2. 3.2.2 Reverse Drive
      3. 3.2.3 Reverse Acceleration Parameters
      4. 3.2.4 Reverse Drive Current Limits
      5. 3.2.5 Reverse Drive Handoff Threshold
      6. 3.2.6 Reverse Drive Open Loop Deceleration (REV_DRV_OPEN_LOOP _DEC)
    3. 3.3 Coasting (Hi-Z)
    4. 3.4 Brake
      1. 3.4.1 Brake Config (BRK_CONFIG)
  7. 4Feature Availability of MCx Devices
    1. 4.1 FOC Family (MCF83xx devices)
    2. 4.2 TRAP Family (MCT83xx devices)
  8. 5Summary
  9. 6References

3.1 Initial Speed Detection Module

When pre-startup begins, with ISD enabled, the back-EMF(BEMF) induced needs to be sensed to extract direction and speed information. The following configurations affect the robustness of the ISD module.

Table 3-1 ISD Tuning Parameters
Tuning Parameter Sub-Feature Description Tuning Considerations
ISD_EN Enables initial motor speed and direction detection Enable if frequent start-stop requests part of operation and there is possibility of motor windmilling at the time of start. Enable for high inertia applications like fans
FAST_ISD_EN Enable fast speed detection during ISD.

To be enabled when fast startup time of less than 100ms is required.

Due to lesser BEMF samples than normal ISD, some angle inaccuracy is observed occasionally leading to initial current spike or reverse rotation.
ISD_STOP_TIME Persistence time for declaring motor has stopped.

Start with low persistence time settings.

Noise in the sensed motor BEMF can cause erroneous motor state detection. Increase to improve reliability.

Decrease for low inertia motor to allow faster speed and direction detection before the BEMF signal decays.

If motor detected stationary even when run command issued with sufficient speed decrease these settings.
ISD_RUN_TIME Persistence time for declaring motor is running
ISD_TIMEOUT Timeout in case ISD is unable to reliably detect speed or direction

Keep timeout times high to allow sufficient time to detect the speed of the motor if the application allows.

If kept too low, ISD sometimes fails to detect speed and direction especially with high ISD_RUN_TIME settings leading to stop and start instead of resync with the drive.
ISD_BEMF_FILT_ENABLE Enable BEMF Filter during ISD Keep BEMF filtering enabled for reliable speed and direction detection especially for motors with non-sinusoidal BEMF.
STAT_DETECT_THR Sets the BEMF threshold below which motor is detected to be stationary.

Set STAT_DETECT_THR with some margin to allow some time for ISD execution and persistence times.

Note: BEMF generated = BEMF constant of the motor * motor speed. Speed below which the motor is detected stationary can be calculated by dividing the STAT_DETECT_THR with BEMF constant.

If set too low, then motor BEMF can be unreliable after ISD is completed leading failed startup.

If set too high, a motor coasting with sufficient BEMF can be detected as stationary.
DIR_CHANGE_MODE Dictates the flow when a direction change command is received. Decides whether to go through ISD routine or use reverse drive to change motor direction while driving continuously. Set to 1b if direction change is part of application use case to decelerate motor in a controlled manner and change direction. Otherwise the recommendation is to coast and brake to stop the motor before changing drive direction.