MCT8317A datasheet(31/161 Pages) TI1

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8.3.8.1 Case 1 – Motor is Stationary

If the motor is stationary, the commutation must be initialized to be in phase with the position of the motor. The

MCT8317A provides various options to initialize the commutation logic to the motor position and reliably start the

motor.

• The align and double align techniques force the motor into alignment by applying a voltage across a

particular motor phase to force the motor to rotate in alignment with this phase.

• Initial position detect (IPD) determines the position of the motor based on the deterministic inductance

variation, which is often present in BLDC motors.

• The slow first cycle method starts the motor by applying a low frequency cycle to align the rotor position to

the applied commutation by the end of one electrical rotation.

MCT8317A also provides a configurable brake option to ensure the motor is stationary before initiating one of

the above start-up methods. Device enters open loop acceleration after going through the configured start-up

method.

8.3.8.2 Case 2 – Motor is Spinning in the Forward Direction

If the motor is spinning forward (same direction as the commanded direction) with sufficient speed (BEMF),

the MCT8317A resynchronizes with the spinning motor and continues commutation by going directly to closed

loop operation. By resynchronizing to the spinning motor, the user achieves the fastest possible start-up time

for this initial condition. This resynchronization feature can be enabled or disabled through RESYNC_EN. If

resynchronization is disabled, the MCT8317A can be configured to wait for the motor to coast to a stop and/or

apply a brake. After the motor has stopped spinning, the motor start-up sequence proceeds as in Case 1,

considering the motor is stationary.

8.3.8.3 Case 3 – Motor is Spinning in the Reverse Direction

If the motor is spinning in the reverse direction (the opposite direction as the commanded direction), the

MCT8317A provides several methods to change the direction and drive the motor to the target speed reference

in the commanded direction.

The reverse drive method allows the motor to be driven so that it decelerates through zero speed. The motor

achieves the shortest possible spin-up time when spinning in the reverse direction.

If reverse drive is not enabled, then the MCT8317A can be configured to wait for the motor to coast to a stop

and/or apply a brake. After the motor has stopped spinning, the motor start-up sequence proceeds as in Case 1,

considering the motor is stationary.

Note

Take care when using the reverse drive or brake feature to ensure that the current is limited to an

acceptable level and that the supply voltage does not surge as a result of energy being returned to the

power supply.

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MCT8317A

SLLSFQ2 – JANUARY 2023

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MCT8317A Datasheet(PDF) 31 Page - Texas Instruments