Note
Determining number of motor poles without a motor datasheet:
1. Use a lab power supply and make sure the current limit is set to less than the motor rated current.
Do not turn on the supply
2. Connect V+ of the supply to phase A and V- of the supply to phase B of the motor. Any 2 of the 3
phases can be chosen at random if they are not labeled
3. Turn on supply The rotor should have settled at one position with the injecting current.
4. Manually rotate the rotor until rotor snaps to another settle position. It will have several settle-
down positions around one mechanical cycle
5. Count the number of settle-down positions for one fully mechanical cycle, which is the number of
pole pairs. Multiplying by two calculates the number of poles.
Be careful of gearing systems within a motor. The gearing ratio will determine how many rotor
revolutions correlate to the shaft’s mechanical revolution.
3.4 Fault Configuration
3.4.1 Cycle by cycle current limit (ILIMIT)
Cycle by cycle current limit provides a means of controlling the amount of current delivered to the motor. This
is useful when the system must limit the amount of current pulled from the power supply during motor start-up.
The cycle by cycle current-limit limits the current applied to the motor from exceeding the configured threshold.
Configure Cycle by cycle current limit [ILIMIT] to the rated peak phase current of the motor. Check the motor
datasheet for the rated peak phase current in Amps. Use
to choose the correct ILIMIT in volts.
ILIMIT V = Cycle by cycle current limit A × CSA_GAIN
v
A
(2)
If the motor is unable to reach the maximum speed, increase ILIMIT in steps until the motor reaches maximum
speed.
3.5 Testing for successful startup into closed loop
1.
Apply a nonzero speed command
a. If the Speed input mode is I2C, change the “I2C Speed Command Percentage” to a non-zero value.
Once the speed command is issued, the device will start commutating and the motor should start
spinning that is proportional to the I2C Speed Command Percentage.
b. If the speed input mode is Analog, rotate the Speed Control potentiometer (R4) clockwise to control
the motor speed. Once the speed command is issued, the device will start commutating and the motor
should start spinning that is proportional to the voltage on the Speed Pin.
c. If the speed input mode is PWM, apply PWM signal to the speed pin with a given duty cycle with a low of
0 V to a high of 2.2 V (min). Once the speed command is issued, the device will start commutating and
the motor should start spinning that is proportional to the duty cycle.
2.
Check if motor spins in closed loop at commanded speed.
In closed loop, the motor should spin at the commanded speed and there should not be any faults triggered.
a. Enable the “Auto read fault status” toggle button towards the top right corner of the GUI. Then monitor
the Fault Status in the side panel to the right.
If no fault gets triggered, skip
and proceed to
.
3.
Prepare device for fault handling if any fault gets triggered.
If the motor failed to spin successfully in closed loop, check the fault status.
a. Set zero speed command by turning off the PWM, turning the potentiometer completely
counterclockwise, or setting the I2C command percentage to 0%.
b. Clear the fault status registers by clicking on the “Clear” button in the Fault Status side panel to the right
as shown in
Essential Controls
SLLU336 – MAY 2021
MCT8316A Tuning Guide
9
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