MCT8317A datasheet(39/161 Pages) TI1

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the motor generates sufficient BEMF to allow the BEMF zero-crossing based commutation control to accurately

drive the motor.

Speed (t) = A1 * t + 0.5 * A2 * t2

(2)

8.3.9.4.6 Transition from Open to Closed Loop

MCT8317A has an internal mechanism to determine the motor speed for transition from open loop commutation

to BEMF zero crossing based closed loop commutation. This feature of automatically deciding the open to

closed handoff speed can be enabled by configuring AUTO_HANDOFF to 1b. If AUTO_HANDOFF is set to 0b,

the open to closed loop handoff speed needs to be configured by OPN_CL_HANDOFF_THR. The closed loop in

this section does not refer to closed speed loop - it refers to the commutation control changing from open loop

(equation based) to closed loop (BEMF zero crossing based).

8.3.10 Closed Loop Operation

In closed loop operation, the MCT8317A drives the motor using trapezoidal commutation. The commutation

instant is determined by the BEMF zero crossing on the phase which is not driven (Hi-Z). The duty cycle of the

applied motor voltage is determined by DUTY OUT (see Motor Control Input Options).

8.3.10.1 120o Commutation

In 120o commutation, each phase is driven for 120o and is Hi-Z for 60o within each half electrical cycle as

shown in Figure 8-25. In 120o commutation there are six different commutation states. 120o commutation can

be configured by setting COMM_CONTROL to 00b. MCT8317A supports different modulation modes with 120o

commutation which can be configured through PWM_MODUL.

Phase

PHASE VOLTAGE

PHASE CURRENT

Commuta on point

Back-EMF zero crossings

Figure 8-25. 120o commutation

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MCT8317A

SLLSFQ2 – JANUARY 2023

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