SLLA576 June   2022 DRV10987 , MCF8316A , MCT8316A

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Design Challenges and Solutions
    1. 2.1 Minimizing Motor Startup Time
      1. 2.1.1 Align
      2. 2.1.2 Initial Position Detect (IPD)
    2. 2.2 Minimizing Acceleration and Deceleration Slew Rate
    3. 2.3 Improving System Efficiency by Minimizing Power Losses
  5. 3References

2.1.1 Align

Below are the steps to tune the motor to achieve faster startup time using Align as the motor startup method:

  1. Select align as the motor startup method in [MTR_STARTUP].
  2. Configure align time [ALIGN_TIME] to 5 ms.
    Note: Ensure the rotor settles to a position and does not oscillate. If the rotor oscillates before spinning in open loop, increase the align time [ALIGN_TIME].
  3. Select Open loop current limit [OL_ILIMIT] to be the same as cycle by cycle current limit [ILIMIT].
    Note: If the device triggers cycle by cycle current limit [CBC_ILIMIT], it is recommended to increase [ILIMIT] up to the stall current of the motor. Configuring this to a value higher than motor stall current might overheat or damage the motor.
  4. Increase Open loop acceleration coefficient A1 [OL_ACC_A1] and Open loop acceleration coefficient A2 [OL_ACC_A2].
    Note: A1 and A2 can be increased until open loop current reaches Lock detection current threshold [LOCK_ILIMIT]. Open loop current can be measured using oscilloscope.

    Increasing Open loop acceleration coefficient A1 [OL_ACC_A1] and Open loop acceleration coefficient A2 [OL_ACC_A2] might trigger LOCK_LIMIT or CBC_ILIMIT. If this happens, reduce A1 and A2 until LOCK_LIMIT no longer triggers.

For ultra-fast startup time (less than 100 ms) it is recommended to follow below steps:

  1. Disable auto-handoff [AUTO_HANDOFF].
  2. Configure Open loop handoff cycles [OL_HANDOFF_CYCLES] to 3.
  3. Configure INTEG_ZC_METHOD to Integration.
  4. Enable Dynamic degauss [DYN_DEGAUSS_EN].
  5. Configure open to closed loop handoff threshold [OPN_CL_HANDOFF_THR] to a value lesser than or equal to 20 Hz.

For startup times above 100 ms, it is recommended to follow below steps:

  1. Enable auto-handoff [AUTO_HANDOFF].
  2. Configure Open loop handoff cycles [OL_HANDOFF_CYCLES] to 6.
  3. Enable Dynamic degauss [DYN_DEGAUSS_EN].
    Note: If Abnormal speed fault [ABN_SPEED] gets triggered, it is recommended to decrease open loop acceleration constants [OL_ACC_A1] and [OL_ACC_A2] and also retune IPD by increasing the IPD current threshold [IPD_CURR_THR] and IPD repeat times [IPD_REPEAT].
  4. Increase Closed loop acceleration rate [CL_ACC]
Note: Closed loop acceleration rate [CL_ACC] can be increased until closed loop current reaches Lock detection current threshold [LOCK_ILIMIT]. Closed loop current can be measured using oscilloscope. Increasing closed loop acceleration rate [CL_ACC] might trigger LOCK_LIMIT. If this happens, reduce closed loop acceleration rate [CL_ACC] until no longer triggers.

Figure 2-1 shows the phase current, FG and Speed curve when the motor is started using Align as the startup method. Time taken for the motor to accelerate to 100% duty cycle is around 46 ms.

GUID-20220610-SS0I-TT6L-N7RN-4P9G6VX0BRSK-low.png Figure 2-1 Startup Time Using Align as Motor Startup Method