4.3.11 Maximizing Thermal Efficiency and Increasing Thermal Performance
Thermal performance can be improved by minimizing power dissipation. Power dissipation across R
DS(on),
Switching losses and operating supply current dissipation are the major sources of Power dissipation in
MCF8316A. Power dissipation across R
DS(on)
is fixed as MOSFETs are integrated in MCF8316A. 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.
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.
4.3.12 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].
4.3.13 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: MCF8316A 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.
www.ti.com Basic Controls
SLLU335A – AUGUST 2021 – REVISED JANUARY 2022
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MCF8316A Tuning Guide 21
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