MCT8316A 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, it is required to spin the motor in specific direction for desired
results. For such applications, it is recommended 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]
4.3.3 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 initialize the motor. With the proper IPD setting, the motor startup is also faster. While this
function is suitable for motors with high inertia, such as heavy blades (for example: a ceiling or appliance fan),
it is not suitable for motors with low inertia, such as small blades (for example: a computer fan), because the
current injection will cause the motor to shake, resulting in the IPD not being accurate.
In applications where the acoustic noise generated by IPD is not acceptable during startup, it is recommended 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 might result in rotor movement, vibration and noise. It is recommended 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 should not be higher than
the rated current of the motor. Use
to choose the correct IPD_CURR_THR.
IPD_CURR_THR V = IPD current tℎresℎold A × CSA_GAIN
V
A
(3)
Step 3: Select IPD clock value [IPD_CLK_FREQ]. The 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.
Looking at Figure 8, the current does not settle completely, which means the clock is too fast for this motor. This
will result in IPD not being able to reliably identify the initial position of the motor.
Step 4: Select IPD Advance angle [IPD_ADV_ANGLE]. This decides how much angle to be added to IPD vector.
To start with, choose smaller value to get smoother spin-up. Highest start up torque is achieved with 90-degree
advance input.
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, it is recommended to check if
motor is connected to the device. If the fault still persists, it is recommended 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, it is recommended to decrease the IPD Clock value [IPD_CLK_FREQ].
Step 5: Select IPD Advance Angle [IPD_ADV_ANGLE]. It is recommended to Start with 90⁰ to get maximum
startup torque. If there is sudden jerk observed during startup, then it is recommended to reduce the angle to 60⁰
or 30⁰ for a smoother startup.
Basic Controls
SLLU336 – MAY 2021
MCT8316A Tuning Guide
15
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