Texas Instruments MCF8315A User manual

User's Guide
MCF8315A Tuning Guide
ABSTRACT
This Tuning guide provided step by step guidence to setup MCF8315EVM, connect MCF8315A GUI to the EVM
and tune a 3-phase Brushless DC motor using MCF8315A.
Table of Contents
1 Introduction.............................................................................................................................................................................2
1.1 Hardware and GUI Setup...................................................................................................................................................2
2 Essential Controls.................................................................................................................................................................. 5
2.1 Recommended Default Values...........................................................................................................................................5
2.2 Device and Pin Configuration.............................................................................................................................................5
2.3 Control Configuration - Motor Parameters......................................................................................................................... 6
2.4 Control configuration - Closed Loop...................................................................................................................................6
2.5 Testing for Successful Startup into Closed Loop................................................................................................................6
2.6 Fault Handling.................................................................................................................................................................... 8
3 Basic Controls.......................................................................................................................................................................11
3.1 Device and Pin Configuration...........................................................................................................................................11
3.2 System Level Configuration..............................................................................................................................................11
3.3 Control Configurations..................................................................................................................................................... 13
List of Figures
Figure 1-1. Simplified Schematic of MCF8315A..........................................................................................................................2
Figure 1-2. MCF8315EVM Jumper Configuration....................................................................................................................... 3
Figure 1-3. MCF8315EVM External Configuration...................................................................................................................... 4
Figure 2-1. Fault Status............................................................................................................................................................... 7
Figure 2-2. Motor Resistance...................................................................................................................................................... 8
Figure 2-3. Motor Inductance.......................................................................................................................................................8
Figure 2-4. Motor BEMF Constant...............................................................................................................................................9
Figure 2-5. Phase Current Waveform Showing a Spike due to Short Circuit............................................................................ 10
Figure 3-1. Phase current and FFT - Dead time compensation disabled.................................................................................. 12
Figure 3-2. Phase current and FFT - Dead time compensation enabled...................................................................................12
Figure 3-3. Power Supply voltage and phase current waveform when AVS is disabled............................................................13
Figure 3-4. Power Supply voltage and phase current waveform when AVS is enabled............................................................ 13
Figure 3-5. MPET - Phase current.............................................................................................................................................14
Figure 3-6. IPD current waveform during Rand L measurement............................................................................................... 14
Figure 3-7. Reverse Drive Function...........................................................................................................................................15
List of Tables
Table 2-1. Recommended Default Values....................................................................................................................................5
Trademarks
All trademarks are the property of their respective owners.
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1 Introduction
The MCF8315A provides three half-H-bridge integrated MOSFET drivers with sensorless FOC control to drive
a three-phase brushless DC (BLDC) motor at 12-V/24-V DC rails or battery powered applications. The device
integrates three current-sense amplifiers (CSA) with integrated current sense for sensing the three phase
currents of BLDC motors to achieve optimum FOC control. Simplified schematic of MCF8315A is shown in
Figure 1-1.
MCT8315A
MOSFETs
Buck/LDO Regulator
Integrated Current Sensing
EEPROM
Sensorless
Trap
DIRECTION
BRAKE
I2C
Optional during operation for
I2C speed, diagnostics, or on-
the-fly configuration
PWM, analog, frequency or
commanded over I2C
SPEED
FG
Speed feecback
nFAULT
A
B
C
4.5 to 35 V (40 V abs max)
4 A peak output current,
typically 12 to 24 V
Buck out
3.3 or 5.0 V, up to 170 mA
A
LDO out
3.3 V, up to 20 mA
B
C
b
d
β
α
Figure 1-1. Simplified Schematic of MCF8315A
This tuning guide provides the steps to tune a 3-phase BLDC motor using the MCF8315A. The tuning process
is classified into two sections: Essential controls and Basic controls. This process is also detailed in the Guided
tuning section in the GUI.
•Essential controls: Tuning steps to successfully spin the motor in closed loop.
•Basic controls: Tuning steps to conform to use-case and explore features in the device.
1.1 Hardware and GUI Setup
Below are the items that are required to run through this tuning guide.
1. MCF8315EVM Board.
2. A computer with the MCF8315A_GUI installed.
3. A motor to be tuned using this process. It is reccomended to have motor data sheet but it is not mandatory.
4. A DC Power Supply rated for the motor.
5. Basic lab equipment such as a Digital Multimeter (DMM), Oscilloscope, current probe and voltage probes.
1.1.1 Jumper Configuration
Confirm the hardware is configured according to the jumper configuration as shown in Figure 1-2. Red boxes
indicate where jumpers are installed on the EVM.
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Figure 1-2. MCF8315EVM Jumper Configuration
1.1.2 External Connections
Connect the motor to J8 (connections A, B, and C). If the motor has a center tap connection or wires for
Hall-effect sensors, leave these wires unconnected. Supply a voltage compliant with the Power Supply Voltage
(VM) range using J7. Recommended voltage range for the device is 4.5 V – 35 V.
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Figure 1-3. MCF8315EVM External Configuration
1.1.3 Connecting to the GUI
1.1.3.1 Connect to computer
Confirm the EVM is powered on (VM) before connecting USB cable. Plug in the micro-USB, from the computer
that holds the GUI, to the USB Connector (J2) on the EVM.
1.1.3.2 Connect to the GUI
The GUI automatically connects to the EVM, as shown on the status bar located on the bottom of this GUI.
If the GUI doesn't connect automatically, please confirm that the "FTDI" serial port is selected by going to the top
menu "Options -> Serial Port ...". Then click on the chain link icon on the left of the status bar to connect to the
EVM.
1.1.3.3 Verify Hardware Connection
After the GUI establishes connection with the EVM through USB, you can verify the communication with the
MCF8315 device by clicking on the "Read All Registers" button on the top right of this GUI. After a few seconds,
the GUI indicates with a pop-up notification that all registers have been read back successfully.
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2 Essential Controls
The goal of this section is to help customers spin their motor successfully in closed loop. This section provides
standardized steps to tune parameters for successful Motor spin-up in closed loop.
Closed loop is defined as the sensorless closed loop where motor spins at the commanded speed.
2.1 Recommended Default Values
Launch the MCF8315A EVM GUI. Load the recommended default values that are listed in Table 2-1.
Table 2-1. Recommended Default Values
Address Name Address Recommended Value
ISD_CONFIG 0x00000080 0x64738C20
REV_DRIVE_CONFIG 0x00000082 0xA8200000
MOTOR_STARTUP1 0x00000084 0x0B6807D0
MOTOR_STARTUP2 0x00000086 0xA306600C
CLOSED_LOOP1 0x00000088 0x0D3201B5
CLOSED_LOOP2 0x0000008A 0x9BAD0000
CLOSED_LOOP3 0x0000008C 0x00000000
CLOSED_LOOP4 0x0000008E 0x00000000
SPEED_PROFILES1 0x00000094 0x00000000
SPEED_PROFILES2 0x00000096 0x00000000
SPEED_PROFILES3 0x00000098 0x00000000
SPEED_PROFILES4 0x0000009A 0x00000000
SPEED_PROFILES5 0x0000009C 0x00000000
SPEED_PROFILES6 0x0000009E 0x00000000
ALGO_CTRL1 0x000000EA 0x00000000
FAULT_CONFIG1 0x00000090 0xBEC80106
FAULT_CONFIG2 0x00000092 0xF0D00888
PIN_CONFIG 0x000000A4 0x00000000
DEVICE_CONFIG1 0x000000A6 0x00000000
DEVICE_CONFIG2 0x000000A8 0x0000B000
PERI_CONFIG1 0x000000AA 0xC1C01F00
GD_CONFIG1 0x000000AC 0x9C450100
GD_CONFIG2 0x000000AE 0x80200000
INT_ALGO_1 0x000000A0 0xA433407D
INT_ALGO_2 0x000000A2 0x000001A7
MTR_PARAMS 0x000000E6 0x00000000
2.2 Device and Pin Configuration
2.2.1 Speed Input Mode
MCF8315A provides four options to configure the input speed command.
• Analog input on SPEED pin by varying amplitude of input signal
• PWM input on SPEED pin by varying duty cycle of input signal
• Over I2C by configuring [DIGITAL_SPEED_CTRL]
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• Frequency input on SPEED pin by varying frequency of input signal
Configure the speed input [SPEED_MODE] register to select the desired 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 corresponds to 100% speed command.
Note that even when [SPEED_MODE] is configured as Analog input, PWM input, or Frequency input, the
[OVERRIDE] toggle can still be used to override the speed input using the in the I2C Control Section in GUI.
2.3 Control Configuration - Motor Parameters
2.3.1 Maximum Motor Electrical Speed (Hz)
Using the motor’s data sheet, 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 converts
the motor mechanical speed in RPM to motor electrical speed in Hz using Equation 1 .
fElectrical =nPolePairs ∙ ωMecℎanical
60  (1)
Where:
• ωMechanical is the mechanical speed in units revolutions per minute (RPM)
• fElectrical is the electrical speed in units of hertz (Hz)
• nPolePairs is the number of motor pole pairs
Note
Determining number of motor poles without a motor data sheet:
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 settles at one position with the injecting current.
4. Manually rotate the rotor until rotor snaps to another settle position. The rotor has 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 determines how many rotor revolutions
correlate to the shaft’s mechanical revolution.
2.4 Control configuration - Closed Loop
2.4.1 Current Limit for Torque PI Loop
The current limit for torque PI loop is the 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 data sheet
for the rated peak phase current of the motor in Amps. The range of current limit values that can be configured in
MCF8315A is between 0.078125 A and 5 A.
If your motor current rating falls between two dropdown settings, then choose the higher setting.
2.5 Testing for Successful Startup into Closed Loop
1. Apply a nonzero speed command
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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 starts commutating and the motor starts 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 starts commutating and the motor starts
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 starts commutating and the
motor starts spinning that is proportional to the duty cycle.
2. Wait for MPET to estimate motor electrical parameters.
The Motor Parameter Extraction Tool (MPET) will attempt to measure the motor resistance, inductance, and
Motor BEMF constant (Ke) and populate these parameters automatically during the initial position detect
(IPD) and open loop stage as the rotor speed attempts to accelerate. It usually takes around 10-15 seconds
to estimate motor resistance, inductance and Motor BEMF constant Ke.
3. 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 Section 2.6 and proceed to Section 3.
4. 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 Figure 2-1
Check Section 2.6 for steps to debug faults.
This completes the essential controls section. At the end of this section, user should be able to spin the motor in
closed loop. Save the register settings by clicking File->Save Registers in the GUI. If there were no faults, skip to
Section 3.
Figure 2-1. Fault Status
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2.6 Fault Handling
Below are the faults that can possibly get triggered based on the default register configuration specified in Table
2-1.
2.6.1 MPET IPD Fault [MPET_IPD_Fault]
This fault gets triggered when there is no motor connected to the phase pins of the device or when the MPET
IPD Current threshold [MPET_IPD_CURRENT_LIMIT] is set low for motors with high resistance. If this fault is
triggered, then please follow the below suggestions.
Step 1: After confirming this fault triggers consistently from multiple start up attempts, check if all the phases of
the motor are connected to the phase pins of the device.
Step 2: If the fault persists, increase the MPET IPD Current threshold [MPET_IPD_CURRENT_LIMIT]
Step 3: If the fault still persists, check motor data sheet for motor resistance and inductance. Open the “Control
configuration – Motor Parameters” tab in All tuning settings section in the GUI and program motor phase
resistance and motor phase inductance.
Step 4: If the motor does not have a data sheet, then measure the phase to phase resistance across any two
phases using a Digital Multimeter and calculate the phase resistance by dividing the phase to phase resistance
by 2 as shown in equation Equation 2. The motor phase resistance refers to the equivalent phase to center tap
resistance, RPH as shown in Figure 2-2. This measurement holds good for both star wound and delta wound
motors.
RPH Pℎaseresistance  = RPH_PH PℎasetoPℎaseresistance
2(2)
Phase A
Phase B
Phase C
RPH_PH
RPH_PH
RPH_PH
RPH
RPH
RPH
CT
Figure 2-2. Motor Resistance
To know the motor inductance, measure the phase to phase inductance at 1 kHz across any two phases using
an LCR meter. Calculate the phase inductance by dividing the phase to phase inductance by 2. Motor phase
inductance refers to the inductance from the phase output to the center tap, LPH as shown in Figure 2-3. For
motors with different phase-phase inductances, measure all three phase to phase inductances and calculate
their average and use this value as the phase to phase inductance. This measurement holds good for both star
wound and delta wound motors.
LPH_PH
Phase A
Phase B
Phase C
LPH_PH
LPH_PH
LPH
LPH
LPH
CT
Figure 2-3. Motor Inductance
2.6.2 MPET BEMF Fault [MPET_BEMF_Fault]
This fault gets triggered when motor stalls while running in open loop for BEMF estimation. If this fault is
triggered, then please follow the below suggestions.
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Step 1: Increase MPET Open loop current reference [MPET_OPEN_LOOP_CURR_REF]
Step 2: Decrease MPET open loop slew rate [MPET_OPEN_LOOP_SLEW_RATE]
Step 3: If this fault persists, check motor data sheet for motor BEMF constant in mV/Hz and program Motor
BEMF Constant [MOTOR_BEMF_CONST] in the “Control configuration – Motor Parameters” tab in All tuning
settings section in the GUI.
Equation 3 and Equation 4 can be used to convert Ke in mV/rpm and torque constant to Ke in mV/Hz.
BEMFConstantinmV
Hz =BEMFConstantmV rpm ×60
Polepairs (3)
BEMFconstantmV
Hz =Torqueconstant mNm
A×  2π
Polepairs (4)
Step 4: If the motor does not have a data sheet, then measure the voltage across any two phases of the
motor using an oscilloscope by manually spinning the motor. A sinusoidal or trapezoidal voltage appears on the
oscilloscope. Measure the peak voltage EPH in milli-volts and time period TE in seconds as shown in Figure 2-4.
Calculate BEMF constant Ke as shown in Equation 5.
Phase A
Phase B
Phase C
CT
LPH
RPH
EPH_A
LPH
RPH
EPH_C
LPH RPH
EPH_B
EPH
TE
KtPH_N = (1/sqrt(3)) *EPH * TE
LPH
RPH
EPH_A
LPH
RPH
EPH_B
LPH
RPH
EPH_C
Figure 2-4. Motor BEMF Constant
BEMFConstantKe =EPH ×TE
3(5)
2.6.3 Abnormal BEMF Fault [ABN_BEMF]
This fault gets triggered when the difference between estimated and expected back-EMF exceeds the abnormal
BEMF threshold % [ABNNORMAL_BEMF_THR]. For example, if the expected BEMF calculated from Ke is 100
mV and the programmed abnormal BEMF threshold is 40%, this fault gets triggered when the estimated BEMF
is <60 mV or >140 mV. This also means the fault can get triggered when the programmed Ke is inaccurate.
Step 1: Estimated BEMF voltage drops when the motor speed drops. Motor speed can drop due to load
dynamics (sudden change in load). For applications with load dynamics, we expect speed to drop and recover
back. Because the speed drops, the BEMF voltage also drops and can trigger this fault. For such applications,
setting the Abnormal BEMF threshold to 70% is reccomended to avoid triggering this fault.
Step 2: This fault can get triggered if the programmed Ke is inaccurate. Follow steps recommended in Section
2.6.2 to obtain accurate Ke.
2.6.4 Lock Current Limit [LOCK_LIMIT]
This fault gets triggered when the motor is loaded above the stall torque of the motor.
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We recommend to check the motor data sheet for stall torque and load the motor below the stall torque specified
in the data sheet. If the load torque is still within the stall torque, we recommend to increase the Lock_ILIMIT in
the Control Configuration – Control Fault settings in the All tuning Settings page.
2.6.5 Hardware lock Current Limit [HW_LOCK_LIMIT]
This fault gets triggered when there is a spike in the phase current due to short circuit as shown in Figure 2-5.
Short circuit can be due to phase to phase, phase to GND or Vm to GND short. Another reason to trigger this
fault is incorrect speed loop and current loop PI controller gains.
Figure 2-5. Phase Current Waveform Showing a Spike due to Short Circuit
Step 1: Program Speed loop Kp [SPD_LOOP_KP], Speed loop Ki [SPD_LOOP_KI], current loop Kp
[CURR_LOOP_KP] and current loop Ki [CURR_LOOP_KI] to zero. This enables auto calculation of speed loop
and current loop PI controller gains.
Step 2: If the fault still persists, check the continuity across phase to phase, phase to GND or Vm to GND to
make sure there is no short across these terminals.
2.6.6 No Motor Fault [NO_MTR]
This fault gets triggered when the phase current is below No motor lock threshold % of base current.
Step 1: Make sure the motor phases are connected to J5 or TP9, TP10, or TP11.
Step 2: If the fault persists, set the No-Motor lock current threshold [NO_MTR_THR] to 0.03125A.
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3 Basic Controls
The goal of this section is to provide customers tuning guidance to conform to use-case and explore various
features in the device.
Note
the user is expected to skip the subsection use-cases and scenarios that do not apply to the system or
end equipment.
3.1 Device and Pin Configuration
3.1.1 Power Saver or Sleep Mode for Battery Operated Applications
MCF8315A can be configured to be in Sleep mode or Standby mode. For applications that operate using
batteries, Sleep and Standby mode are important to save power while the device is not spinning the motor.
MCF8315A enters sleep mode when speed input is held continuously below the speed threshold for
SLEEP_ENTRY_TIME.
In sleep mode, all motor outputs are disabled, the charge pump is disabled, the AVDD regulator is disabled,
and the serial communication bus is disabled. MCF8315A can be configured to be in sleep mode by
configuring register bits DEV_MODE. Please note that in Sleep mode, GUI loses connectivity as there is no
I2C communication.
3.1.2 Direction and Brake Pin Override
Direction and Brake pin override is helpful in applications where it is not intended for the users to affect the
direction and brake pins in the device. In such cases, it is recommended to override both pins and configure
them via EEPROM.
Direction pin in MCF8315A can be overwritten by configuring [DIR_INPUT]. Configuring [DIR_INPUT] to 01b
overwrites Hardware pin to clockwise rotation if motor phases A, B and C are connected to OUTA, OUTB
and OUTC respectively. Commutation sequence in clockwise direction is OUTA-OUTB-OUTC. Configuring
[DIR_INPUT] to 10b overwrites Hardware pin to anti-clockwise rotation if motor phases A, B and C are
connected to OUTA, OUTB and OUTC respectively. Commutation sequence in anti-clockwise direction is OUTA-
OUTC-OUTB.
BRAKE pin in MCF8315A can be overwritten by configuring [BRAKE_INPUT]. Configuring [BRAKE_INPUT]
to 01b overwrites Hardware pin to low side brake/Align according to [BRAKE_PIN_MODE]. Configuring
[BRAKE_INPUT] to 10b overwrites Hardware pin and not low side brake/align.
In Low side braking mode, all the LS FETs are turned ON. In Align braking mode, MCF8315A aligns a motor by
injecting dc current through a particular phase pattern.
3.2 System Level Configuration
3.2.1 Tracking Motor Speed Feedback in Real Time
MCF8315A device provides information about the motor speed through the frequency generator (FG) pin,
which is also known as a TACH (tachometer) out. In MCF8315A, the FG pin behavior is configured through
FG_CONFIG. Configure FG_SEL to output FG signal only in closed loop, both open loop and closed loop, or
only in open loop for the first try. Configure FG_DIV to number of motor poles so that the FG output matches the
motor mechanical speed in Hz.
When FG_CONFIG is configured to 0 (FG active as long as motor is driven), the FG output is active as long as
MCF8315A is driving the motor. FG is not active during a motor stop and coasting condition. In this mode, FG is
released high when MCF8315A enters sleep or standby mode. This mode is useful in applications that require
real time motor speed information as long as MCF is driving the motor.
When FG_CONFIG is configured to 1 (FG active till BEMF drops below FG_BEMF_THR), MCF8315A provides
FG output until BEMF falls below FG_BEMF_THR. The FG output continues to indicate motor speed even if the
motor is not being actively driven. This mode is useful in applications that require motor speed information above
a certain speed, and rotor motion information during the coast and braking conditions.
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For example, if the motor Ke is 5 mV/Hz and the application require measuring motor speed above 4 Hz, then
the user can configure FG_BEMF_THR to 20 mV. Once when the motor speed reaches 4 Hz, the device outputs
FG as the BEMF voltage is at 20 mV at 4 Hz.
3.2.2 Improving Acoustic Performance
Acoustics is audible noise contributed by motor commutation and harmonic frequencies in motor drives. Stator
excitation in motor drivers can generate mechanical resonance at audible frequency ranges leading to audible
noise. Improving acoustic performance is important for applications that require quiet operation. Any distortion in
phase current can translate to audible noise. Phase current distortion can be due to dead time, PWM modulation
scheme or low MOSFET slew rate.
Step 1: Configure PWM Modulation scheme [PWM_MOD] to “Continuous Space Vector Modulation”.
Note
1. In Continuous Space vector modulation, phase current waveform shaping is better but the
MOSFET switching losses is higher.
2. In Discontinuous Space vector modulation, MOSFET switching losses are lower. However, we can
expect phase current distortion for low inductance motors.
Step 2: Enable Dead time compensation [DEADTIME_COMP_EN]
Figure 3-1 shows the phase current waveform when dead time compensation is disabled. Fundamental
frequency of phase current is 40 Hz. Fast Fourier transform (FFT) of phase current plot shows harmonics at
160 Hz and 220 Hz. Figure 3-2 shows the phase current waveform when dead time compensation is enabled.
Phase current looks more sinusoidal and the FFT of phase current plot does not have any harmonics.
Figure 3-1. Phase current and FFT - Dead time
compensation disabled
Figure 3-2. Phase current and FFT - Dead time
compensation enabled
3.2.3 Protecting the Power supply
Protecting the power supply from drawing higher current or potential voltage overshoots is important in battery
operated applications or applications that do not have an internal overcurrent or overvoltage protection built into
the power supply.
Step 1: When the load on the motor increases, device draws higher current from the power supply. For
applications that want to limit the current drawn from the power supply, the recommendation is to Enable Bus
current limit [BUS_CURRENT_LIMIT_ENABLE] and configure the Bus current limit [BUS_CURRENT_LIMIT] to
protect the power supply from drawing higher current.
For example, the requirement to limit the current drawn from power supplies such as batteries as the battery life
depends on the charge or discharge cycles. Enabling bus current limit limits the power supply current by limiting
the speed of the motor.
Step 2: When a command is issued for the motor to decelerate, based on the deceleration rate, the energy from
motor pumps back to the power supply, increasing the supply voltage to possibly unsafe levels for electronics.
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Enable the Antivoltage surge [AVS] to protect the power supply from voltage overshoots which overrides any
deceleration limit set by any other register and automatically apply a safe deceleration rate.
Figure 3-3 shows overshoot in power supply voltage when AVS is disabled. Motor decelerates from 100% duty
cycle to 10% duty cycle at a deceleration rate of 70,000 Hz/sec. Figure 3-4 shows no overshoot in power supply
voltage when AVS is enabled.
Figure 3-3. Power Supply voltage and phase
current waveform when AVS is disabled
Figure 3-4. Power Supply voltage and phase
current waveform when AVS is enabled
3.2.4 Monitoring Power Supply Voltage Fluctuations for Normal Motor Operation
In applications where the power supply may fluctuate, it is recommended to specify the minimum and maximum
power supply voltage range. During an undervoltage condition, the motor might operate in overmodulation region
to achieve the target speed leading to current distortion, inefficiency or noise. During an overvoltage condition,
the MOSFETs, MCF8315A and motor may be stressed with continued operation in high voltage.
Step 1: Keep decreasing the supply voltage till we see a drop in the speed. Measure the bus voltage at which
the speed drops and set MIN_VM_MOTOR to that value. Range of minimum bus voltage that can be configured
is between 4.5 V and 12.5 V.
Step 2: Keep increasing the bus voltage to a point where the motor phase voltage reaches the maximum rated
voltage of the motor. MAX_VM_MOTOR is the bus voltage at which motor phase voltage reaches the maximum
rated voltage of the motor. Range of maximum bus voltage that can be configured is between 20 V and 35 V.
Note
MCF8315A provides an undervoltage recovery mode [MIN_VM_MODE] and an overvoltage recovery
mode [MAX_VM_MODE]. Undervoltage recovery mode can be configured to either automatically clear
Undervoltage fault [MTR_UNDER_VOLTAGE] or latch on Undervoltage fault. Overvoltage recovery
mode can be configured to either automatically clear Overvoltage fault [MTR_OVER_VOLTAGE] or
latch on Overvoltage fault.
3.3 Control Configurations
3.3.1 Motor Parameter Estimation to Minimize Motor Parameter Variation Effects
The MCF8315A uses motor resistance, motor inductance and the motor Back-EMF constant to estimate motor
position in closed loop operation. The MCF8315A has capability of automatically measuring motor parameters
in offline state, rather than having the user enter the values themselves. Offline measurement of parameters
takes place before normal motor operation. Variation in motor parameters can impact the accuracy of motor
position estimation and therefore the motor commutation and rotation. The reccomendation is to estimate the
motor parameters before motor startup to minimize the impact caused due to possible parameter variations.
The MCF8315A has Motor Parameter Extraction Tool (MPET) which estimates the motor phase resistance, the
motor phase inductance and the motor Back-EMF constant. Go to “Control Configuration - Motor parameter
extraction tool (MPET)”.
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Step 1: Enable Measure motor resistance [MPET_R], Measure motor inductance [MPET_L] and Motor BEMF
constant [MPET_Ke].
Step 2: Enable MPET Start command [MPET_CMD]. Make sure the motor is stationary before enabling MPET
start command.
Step 3: After successful motor parameter extraction, copy the estimated parameters to the respective shadow
registers by enabling MPET write to shadow register flag.
Note
1. If the device triggers MPED_IPD_FAULT, increase the MPET IPD Current threshold till the rated
current of the motor.
2. If the device triggers MPED_IPD_FAULT, decrease MPET Open loop slew rate
[MPET_OPEN_LOOP_SLEW_RATE].
3. If the fault still persists, increase MPET Open loop current reference
[MPET_OPEN_LOOP_CURRENT_REF] and decrease MPET Open loop speed reference
[MPET_OPEN_LOOP_SPEED_REF]
Figure 3-5 shows the phase current waveform during motor parameter measurement. Figure 3-6 shows the IPD
current waveform during R, L and Ke measurement. Bottom half of Figure 3-6 shows the IPD current waveform
during R and L measurement. R is measured during the rising of phase current and L is measured during the
falling of phase current. After R and L measurement, motor spins in open loop. Once the speed reaches MPET
open loop speed reference [MPET_OPEN_LOOP_SPEED_REF], motor is coasted. BEMF voltage of all three
phases are measured and Ke is calculated.
Figure 3-5. MPET - Phase current Figure 3-6. IPD current waveform during Rand L
measurement
3.3.2 Initial Speed Detection of the Motor for Reliable Motor Resynchronization
The Initial Speed Detection (ISD) function is used to identify the initial condition of the motor. Prioritize knowing
the initial condition of the motor for reliable resynchronization. Motor resynchronization failures can occur when
the device attempts to start the motor while the motor is coasting or spinning in the direction opposite to the
intended direction of spin. Motors can coast in applications that require frequent motor starts and stops, or if the
motor Is being forced externally or if there is a power interruption. Motors can spin in the direction opposite to
the intended direction of spin if motor phase wires are connected to OUTA, OUTB and OUTC in wrong sequence
or when wrong direction command is issued. Motors with higher inertia coast for a longer period of time. The
recommendation is to have ISD enabled in applications that require frequent motor starts and stops and use
higher inertia motors.
For example, ceiling fan motors have higher inertia due to the fan blades and can coast for long time before
stopping.
Step 1: Enable ISD [ISD_EN]
Step 2: Enable Motor ISD Resynchronize [RESYNC_EN]
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Note
Follow the below recommendations if the motor fails to startup.
1. Increase the Motor Stationary BEMF Threshold [STAT_DETECT_THR].
2. Increase the Motor Stationary Persistence Time [ISD_STOP_TIME].
3. Increase the Motor Run Persistence Time [ISD_RUN_TIME].
4. Increase the Minimum speed threshold to resynchronize to closed loop
3.3.3 Unidirectional Motor Drive Detecting Backward Spin
For applications that require spinning the motor in a specific direction, prioritize knowing if the motor is coasting
or spinning in the direction opposite to the intended direction of spin. MCF8315A reverse drive function acts
to reverse decelerate the motor through zero speed and to accelerate after changing direction until the motor
transitions into closed loop as shown in Figure 3-7.
Reverse Deceleration
Open Loop
Handoff to close loop
Open loop
Close loop
Speed
Time
Handoff to open loop
Figure 3-7. Reverse Drive Function
MCF8315A provides an option to apply brakes and stop the motor while the motor is coasting or spinning in
reverse direction and then accelerate into closed loop after changing the direction.
In applications such as ceiling fans and pumps, the requirement is to spin the motor in specific direction for
desired results. For such applications, the reccomendation is to follow the below recommendations.
Step 1: Enable ISD [ISD_EN]
Step 2: Enable Motor ISD Reverse drive [RVS_DR_EN]
Step 3: Enable reverse resynchronization [RESYNC_EN]
Step 4: Enable Active brake reverse drive [ACTIVE_BRAKE_REV_DRV_EN]
Step 5: Enter the Kp coefficient [ACTIVE_BRAKE_KP] and Ki coefficient [ACTIVE_BRAKE_KI] for Active
braking loop. We recommend to start with Kp coefficient [ACTIVE_BRAKE_KP] as 700 and Ki coefficient
[ACTIVE_BRAKE_KI] as 100.
Step 6: Set bus current limit during active braking [ACTIVE_BRAKE_CURRENT_LIMIT]
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Note
Follow the below recommendations if the motor fails to resynchronize in reverse direction.
1. Increase the reverse deceleration speed threshold to transition to open loop
2. Enable Open loop reverse drive configuration [REV_DRV_CONFIG]
3. Increase the Reverse Drive Open Loop Current Reference
[REV_DRV_OPEN_LOOP_CURRENT]
4. Decrease open loop acceleration coefficient A1 and A2 during reverse drive
5. If the device triggers Lock current limit [LOCK_LIMIT], then increase the open loop current limit
during speed reversal [REV_DRV_OPEN_LOOP_CURRENT]
3.3.4 Preventing Back Spin of Rotor During Startup
For applications where a reverse spin is not acceptable, the Initial Position Detection algorithm (IPD) function
is an alternative way to start up the motor. With the proper IPD setting, the motor startup can be faster than
using align. While this function is applicable for motors with high inertia, such as heavy blades (for example: a
ceiling or appliance fan), the function is not reccomended for motors with low inertia, such as small blades (for
example: a computer fan), because the current injection causes the motor to shake, resulting in the IPD not
being accurate.
In applications where the acoustic noise (“chirp”) generated by IPD is not acceptable during startup, the
reccomendation is to select Slow first cycle as the startup method.
Option 1: IPD
Step 1: If IPD is chosen as startup method, select IPD in the Motor startup option [MTR_STARTUP] in “Control
Configuration – Motor Startup Stationary” tab in the GUI.
Step 2: Select the IPD Current threshold [IPD_CURR_THR]. IPD current threshold is selected based on the
inductance saturation point of the motor. A higher current has better chance to accurately detect the initial
position. However, higher current can result in rotor movement, vibration and noise. The reccomendation is
to start with 50% of the rated current of the motor. If the motor startup is unsuccessful, then we recommend
increasing the threshold till the motor starts up successfully. Note that the IPD current threshold is not be higher
than the rated current of the motor.
Step 3: Select IPD clock value [IPD_CLK_FREQ]. IPD clock defines how fast the IPD pulses are applied. Higher
inductance motors and higher current thresholds need a longer time to settle the current down, so we need set
the clock at a slower time. However, a slower clock makes the IPD noise louder and last longer, so we suggest
setting the clock as fast as possible as long as IPD current is able to settle down completely.
Note
Device triggers IPD timeout faults [IPD_T1_FAULT] and [IPD_T2_FAULT] for motors with very high
inductance, or if the motor is not connected. If this fault gets triggered, the reccomendation is to check
if motor is connected to the device. If the fault still persists, the reccomendation is to set the IPD
release mode [IPD_RLS_MODE] to Tri-state if any overshoot in DC bus voltage is acceptable.
Device triggers IPD Frequency fault [IPD_FREQ_FAULT] if the IPD clock frequency is set too high. If
this fault gets triggered, the reccomendation is to decrease the IPD Clock value [IPD_CLK_FREQ].
Step 4: Select IPD Advance Angle [IPD_ADV_ANGLE]. The reccomendation is to Start with 90⁰ to get maximum
startup torque. If there is sudden jerk observed during startup, then the reccomendation is to reduce the angle to
60⁰ or 30⁰ for a smoother startup.
Option 2: Slow first cycle
Follow below steps if Slow first cycle is chosen as the startup method.
Step 1: Select Slow first cycle in the Motor startup option [MTR_STARTUP] in “Control Configuration – Motor
Startup Stationary” tab in the GUI.
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Step 2: Select Align or Slow first cycle current reference [ALIGN_OR_SLOW_CURRENT_ILIMIT]. Lower current
reference can lose synchronization of motor. Higher current can lead to sustained oscillations for high inertia
motors, or sudden jerky motion for low inertia motors. The reccomendation is to start with 50% of the rated
current of the motor. In applications where the startup torque is high, the motor can lose synchronization. In
such applications, the reccomendation is to increase the current reference. In applications where, sustained
oscillations or sudden jerks are observed, the reccomendation is 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. The reccomendation is 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 can lose synchronization. In
such applications, The reccomendation is to increase the current ramp rate. In applications where, sustained
oscillations or sudden jerks are observed, The reccomendation is 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. The reccomendation is to start with
20% of the maximum speed of the motor. In applications where the startup torque is high, the motor can lose
synchronization. In such applications, The reccomendation is to decrease the frequency. In applications where
jerky motions are observed, The reccomendation is to increase the frequency.
3.3.5 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 Section 3.3.4 (Step 3) for more details.
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]
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Note
LOCK_LIMIT fault handling:
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.
Option 2: Slow first cycle
Step 1: Select Slow first cycle as the motor startup method in [MTR_STARTUP].
Step 2: Select Align or slow first cycle current limit [ALIGN_OR_SLOW_CURRENT_ILIMIT] to be the same as
Current limit for Torque PI loop [ILIMIT].
Step 3: Keep increasing Align or slow first cycle current ramp rate [ALIGN_SLOW_RAMP_RATE] until the open
loop current reaches 100% of the rated current of the motor.
Step 4: Follow Step 5 to Step 9 in Option 1.
3.3.6 Gradual and Smooth Start up Motion
For applications that require slow and gradual startup with lower speed overshoots during handoff, follow the
below recommendations.
Step 1: Decrease Open loop acceleration coefficient A1 [OL_ACC_A1] and Open loop acceleration coefficient
A2 [OL_ACC_A2].
Step 2: Enable Iq ramp down after transition to closed loop [IQ_RAMP_EN]
If there is speed overshoots, it is recommended to decrease ramp rate for reducing difference between
estimated theta and open loop theta [THETA_ERROR_RAMP_RATE].
3.3.7 Improving Speed Regulation
For applications that require better speed regulation, it is recommended to tune Speed loop PI controllers
[SPD_LOOP_KP] and [SPD_LOOP_KI]. Kp coefficient of speed loop [SPD_LOOP_KP] controls the settling time
and speed overshoots. Ki coefficient of Speed loop [SPD_LOOP_KI] controls speed overshoot and ensures
regulation of speed at set value and drives the error to zero. Speed loop PI controller gains can either be
auto-tuned by MCF8315A or tuned manually.
Auto Tuning: MCF8315A auto calculates Speed loop PI controller gains when [SPD_LOOP_KP] and
[SPD_LOOP_KI] are set to zero.
Manual Tuning: Follow below steps to tune Speed loop PI controller gains manually
Step 1: Disable Speed loop [SPEED_LOOP_DIS]
Step 2: Disable closed loop [CLOSED_LOOP_DIS]
Step 3: Issue non-zero speed command to start the motor (refer to Section 2.5, step 1 on how to issue non-zero
speed command). Motor will spin in open loop.
Step 4: Allow the open loop current to settle down and then measure the peak open loop current.
Step 5: Enter 110% of measured peak phase current as the Iq reference when speed loop is disabled
[FORCE_IQ_REF_SPEED_LOOP_DIS]
Step 6: Enable closed loop [CLOSED_LOOP_DIS]. Now the motor will enter closed loop in torque mode.
Stp 7: Adjust the Iq reference [FORCE_IQ_REF_SPEED_LOOP_DIS] such that the motor speed reaches the
maximum speed.
Step 8: Speed loop Kp [SPD_LOOP_KP] is calculated using Equation 6.
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SpeedloopKp=Iqreferenceatmaximumspeed
MaximumElectricalSpeedinHz (6)
Step 9: Speed loop Ki [SPD_LOOP_KI] is calculated using equationEquation 7.
SpeedloopKi = 0.1 × SpeedloopKp (7)
Step 10: Enable speed loop [SPEED_LOOP_DIS]
Note
Tuning speed loop Kp and Ki is experimental. If the above recommendation doesn’t work, then we
recommend to manually tune Speed loop Kp and Ki till the desired results are achieved.
3.3.8 Stopping Motor Quickly
For applications that require stopping the motor quickly, it is recommended to configure Motor stop options
[MTR_STOP] to either High side braking or Low side braking.
Step 1: Configure Motor stop options [MTR_STOP] to either High side braking or Low side braking.
Step 2: Select Speed threshold for BRAKE pin and Motor STOP options. Setting speed threshold to higher
speed would result in FETs carrying large current. Setting speed threshold to lower speed would increase the
stop time of the motor. It is recommended to start with 50% of the maximum speed. If the device triggers
Overtemperature warning [OTW] or Overtemperature shutdown [OTS], it is recommended to decrease the
threshold. If the stop time is too high, it is recommended to increase the threshold.
3.3.9 Preventing Supply Voltage Overshoot During Motor Stop.
For applications that require preventing supply voltage overshoots during motor stop, it is recommended to
select active spin down as Motor stop options. Active spin down can be used as a motor stop option in
applications where fast stop is not required but some amount of inductive energy going back to power supply is
acceptable
Active spin down
Step 1: Configure Motor stop options [MTR_STOP] to Active spin down
Step 2: Configure active spin down speed threshold [ACT_SPIN_THR]. It is recommended to set the
[ACT_SPIN_THR] to 50% of the maximum speed. If there is voltage overshoot seen on the power supply, it
is recommended to decrease the ACT_SPIN_THR till the voltage overshoot reaches acceptable limit.
3.3.10 Protecting Against Rotor Lock or Stall Condition
Follow below recommendations if the motor stalls or gets locked in closed loop when the motor is overloaded.
Increase lock detection current threshold [LOCK_ILIMIT]
Note
MCF8315A provides options to either latch LOCK_LIMIT fault or auto retry for
[AUTO_RETRY_TIMES] after every [LCK_RETRY] seconds. This can be configured in
[LOCK_ILIMIT_MODE]. We have defaulted the auto retry time and lock retry.
3.3.11 Maximizing Thermal Efficiency and Increasing Thermal Performance
Thermal performance can be improved by minimizing power dissipation. Power dissipation across RDS(on),
Switching losses and operating supply current dissipation are the major sources of Power dissipation in
MCF8315A. Power dissipation across RDS(on) is fixed as MOSFETs are integrated in MCF8315A. Please follow
below recommendations to minimize switching losses and operating supply current dissipation.
Step 1: Increase Slew rate [SLEW_RATE]
Please note that increasing Slew rate will increase EMI noise.
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Step 2: Decrease PWM output frequency [PWM_FREQ_OUT]
Please note that decreasing PWM output frequency may lead to discontinuous phase current for very low
inductance motors.
3.3.12 Mitigating Electromagnetic Interference (EMI)
Please follow the below recommendations to mitigate EMI in your system.
Step 1: Decrease Slew rate [SLEW_RATE]
Please note that decreasing Slew rate will increase power dissipation due to switching losses.
Step 2: Enable Spread spectrum Modulation [SSM_DIS].
3.3.13 Faster deceleration
Decelerating the motor quickly requires motor mechanical energy to be extracted and disposed - input DC
voltage increases if this energy is returned to the DC input supply. When active braking is enabled, energy taken
from DC power supply is used to brake the motor - this prevents DC voltage spike during fast deceleration. The
mechanical energy of the motor and energy taken from DC source, both are dissipated within the motor itself.
Follow below steps to decelerate the motor quickly.
Step 1: Enable active braking [ACTIVE_BRAKE_EN].
Step 2: Configure ACTIVE_BRAKE_CURRENT_LIMIT. This sets the maximum limit on the current sourced from
the DC bus during active braking. Active brake current limit should be configured to a value lesser than the
power supply current limit.
Step 3: Configure ACTIVE_BRAKE_BUS_CURRENT_SLEW_RATE. This sets the slew rate of the DC bus
current starting from 0A to ACTIVE_BRAKE_CURRENT_LIMIT.
Step 4: Configure ACTIVE_BRAKE_MOD_INDEX_LIMIT. This sets the modulation index limit below which active
braking will be applied. Above this modulation index, device will apply AVS if AVS is enabled. Setting a higher
modulation index limit will decelerate the motor much faster.
Note
Modulation index [VOLT_MAG] can be read back from ALGO_STATUS register.
Step 5: MCF8315A uses a PI controller to generate the D-axis reference current. Manually tune
ACTIVE_BRAKE_KP and ACTIVE_BRAKE_KI if the active brake current looks unstable.
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