Step 2: Select Align or Slow first cycle current reference [ALIGN_OR_SLOW_CURRENT_ILIMIT]. Lower current
reference may lose synchronization of motor. Higher current may lead to sustained oscillations for high inertia
motors, or sudden jerky motion for low inertia motors. It is recommended to start with 50% of the rated current
of the motor. In applications where the startup torque is high, the motor might lose synchronization. In such
applications, it is recommended to increase the current reference. In applications where, sustained oscillations or
sudden jerks are observed, it is recommended to decrease the current reference.
Step 3: Select Align or slow first cycle current ramp rate [ALIGN_SLOW_RAMP_RATE]. Current reference is
ramped to avoid reverse rotation of the motor. Lower current ramp rate may lose synchronization of motor. A
higher current ramp rate may lead to sustained oscillations for high inertia motors, or sudden jerking motion for
low inertia motors. It is recommended to start with setting up the ramp time to 0.5 sec to ramp to rated current
of the motor. In applications where the startup torque is high, the motor might lose synchronization. In such
applications, it is recommended to increase the current ramp rate. In applications where, sustained oscillations
or sudden jerks are observed, it is recommended to decrease the current ramp rate.
Step 4: Select Frequency of first cycle [SLOW_FIRST_CYC_FREQ]. Lower frequency may give a jerky motion
at startup. Higher frequency may not be able to synchronize the motor. It is recommended to start with 20%
of the maximum speed of the motor. In applications where the startup torque is high, the motor might lose
synchronization. In such applications, it is recommended to decrease the frequency. In applications where jerky
motions are observed, it is recommended to increase the frequency.
4.3.5 Faster Startup Timing
Startup time is the time taken for the motor to reach the target speed from zero speed. For applications that
require quick startup time, we recommend choosing either Initial Position Detection (IPD) or Slow first cycle as
the startup method.
Option 1:
Initial Position Detection (IPD)
Step 1: Select IPD [MTR_STARTUP] as the motor startup method.
Step 2: Increase IPD current threshold [IPD_CURR_THR] to rated current of the motor.
Step 3: Increase IPD clock value [IPD_CLK_FREQ] to higher frequency up to a value where the device does not
trigger IPD frequency fault. Check
Step 4: Select IPD repeating times [IPD_REPEAT] to 1 time.
Step 5: Select Open loop current limit [OL_ILIMIT] to be the same as Current limit for Torque PI Loop [ILIMIT].
If the device triggers Lock current limit [LOCK_LIMIT], it is recommended to increase [LOCK_ILIMIT] upto the
stall current of the motor. Configuring this to a value higher than motor stall current will overheat or damage the
motor.
Step 6: 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. If this happens, reduce A1 and A2 until LOCK_LIMIT no longer triggers.
Step 7: Select Minimum BEMF for handoff [AUTO_HANDOFF_MIN_BEMF] to 0 mV.
If the device triggers Abnormal BEMF [ABN_BEMF] fault, then it is recommended to increase the
[AUTO_HANDOFF_MIN_BEMF].
Step 8: Keep increasing ramp rate for reducing difference between estimated theta and open loop theta to 2
deg/ms.
Step 9: Increase Closed loop acceleration rate [CL_ACC]
Basic Controls
18
MCF8316A Tuning Guide
SLLU335A – AUGUST 2021 – REVISED JANUARY 2022
Copyright © 2022 Texas Instruments Incorporated
