Configure the speed input [SPEED_MODE] register to select the appropriate speed input mode.
If PWM input on SPEED pin is chosen as the speed input, configure SPEED_RANGE_SEL to select the PWM
frequency range.
If Frequency input on SPEED pin is chosen as the speed input, configure INPUT_MAXIMUM_FREQ to select
the maximum PWM frequency. For example, if 10 kHz is chosen as maximum PWM frequency, 10 kHz PWM
signal on SPEED pin will correspond to 100% speed command.
To command the speed via I
2
C, toggle the “Enable Speed Control via I
2
C” in the I
2
C Control Section in GUI.
3.3 Control Configuration - Motor Parameters
3.3.1 Maximum Motor Electrical Speed (Hz)
Using the motor’s datasheet, the user can input the maximum motor electrical speed in Hz. If this data is not
available, the user can input the number of pole pairs and motor mechanical speed in RPM. The GUI will convert
the motor mechanical speed in RPM to motor electrical speed in Hz using
f
Electrical
=
nPolePairs ∙ ωMecℎanical
60
(1)
Where:
• ω
Mechanical
is the mechanical speed in units revolutions per minute (RPM)
• f
Electrica
l
is the electrical speed in units of hertz (Hz)
• n
PolePairs
is the number of motor pole pairs
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 Control configuration - Closed Loop
3.4.1 Current Limit for Torque PI Loop
The current limit for torque PI loop will be same as the rated peak phase current of the motor. Rated peak phase
current is the peak phase current drawn by the motor at rated torque of the motor. Check the motor datasheet for
the rated peak phase current of the motor in Amps. The range of current limit values that can be configured in
MCF8316A is between 0.125 A and 8 A.
If your motor current rating falls between two dropdown settings, then choose the higher setting.
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.
Essential Controls
SLLU335A – AUGUST 2021 – REVISED JANUARY 2022
MCF8316A Tuning Guide
7
Copyright © 2022 Texas Instruments Incorporated
