For example, it is required 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 may be pumped back to the power supply, increasing the supply voltage to possibly unsafe levels for
electronics. Enable the Antivoltage surge [AVS] to protect the power supply from voltage overshoots which will
override any deceleration limit set by any other register and automatically apply a safe deceleration rate.
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.
shows no overshoot in power supply
voltage when AVS is enabled.
Figure 4-3. Power Supply voltage and phase
current waveform when AVS is disabled
Figure 4-4. Power Supply voltage and phase
current waveform when AVS is enabled
4.2.4 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, MCF8316A 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 will be 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
MCF8316A 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.
4.3 Control Configurations
4.3.1 Motor Parameter Estimation to Minimize Motor Parameter Variation Effects
The MCF8316A uses motor resistance, motor inductance and the motor Back-EMF constant to estimate motor
position in closed loop operation. The MCF8316A 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
Basic Controls
14
MCF8316A Tuning Guide
SLLU335A – AUGUST 2021 – REVISED JANUARY 2022
Copyright © 2022 Texas Instruments Incorporated
