Figure 8-19 shows
the motor-start sequence implemented in the MCT8316A device.
Figure 8-19 Motor Starting-Up Flow
Power-On StateThis is the initial state of the Motor Start Sequence (MSS). The MSS starts in this state on
initial power-up or whenever the MCT8316A device comes out of standby or sleep mode.
DIR Change
JudgementIn MCT8316A, if direction change command is detected
at start of MSS, the motor direction detected in ISD is assumed to be opposite to
commanded direction and reverse drive is performed if RVS_DR_EN is set to 1b.
ISD_EN JudgementAfter power-on, the MCT8316A MSS enters the ISD_EN judgement where it checks to see if the initial speed detect
(ISD) function is enabled (ISD_EN = 1b). If ISD is disabled, the MSS proceeds directly
to the BRAKE_EN judgement. If ISD is enabled, MSS advances to the ISD (Is Motor
Stationary) state.
ISD StateThe MSS determines the initial condition (speed, direction of spin) of the motor (see
Section 8.3.10.1). If motor is deemed to be stationary (motor BEMF < STAT_DETECT_THR), the MSS
proceeds to STAT_BRK_EN judgement. If the motor is not stationary,
MSS proceeds to verify the direction of spin.
STAT_BRK_EN JudgementThe MSS checks if the stationary brake function is enabled (STAT_BRK_EN =1b). If the
stationary brake function is enabled, the MSS advances to the stationary brake routine.
If the stationary brake function is disabled, the MSS advances to motor start-up state
(see Section 8.3.10.4).
Stationary Brake RoutineThe stationary brake routine can be used to ensure the motor is completely stationary
before attempting to start the motor. The stationary brake is applied by turning on all
three low-side driver MOSFETs for a time configured by STARTUP_BRK_TIME.
Direction of Spin JudgementThe MSS determines whether the motor is spinning in the forward or the reverse
direction. If the motor is spinning in the forward direction, the MCT8316A proceeds to the RESYNC_EN judgement. If the motor is spinning in the reverse
direction, the MSS proceeds to the RVS_DR_EN judgement.
RESYNC_EN JudgementIf RESYNC_EN is set to 1b, MCT8316A proceeds to BEMF >
RESYNC_MIN_THRESHOLD judgement. If RESYNC_EN is set to 0b, MSS proceeds to HIZ_EN
judgement.
BEMF > RESYNC_MIN_THRESHOLD JudgementIf motor speed is such that BEMF > RESYNC_MIN_THRESHOLD, MCT8316A uses the speed and
position information from the ISD state to transition to the closed loop state (see
Section 8.3.10.2 ) directly. If BEMF < RESYNC_MIN_THRESHOLD, MCT8316A proceeds to STAT_BRK_EN
judgement.
RVS_DR_EN JudgementThe MSS checks to see if the reverse drive function is enabled (RVS_DR_EN = 1). If it
is enabled, the MSS transitions to check speed of the motor in reverse direction. If
the reverse drive function is not enabled, the MSS advances to the HIZ_EN
judgement.
Speed > Open to Closed Loop Handoff
JudgementThe MSS checks to see if the reverse speed is high enough for MCT8316A to decelerate in closed loop. Till the speed (in reverse direction) is high
enough, MSS stays in reverse closed loop deceleration. If speed is too low, then the
MSS transitions to reverse open loop deceleration.
Reverse Closed Loop, Open Loop Deceleration and Zero Speed CrossoverThe MCT8316A resynchronizes in the reverse direction, decelerates the motor in closed loop till
motor speed falls below the handoff threshold. (see Section 8.3.10.3). When motor speed in reverse direction is too low, the MCT8316A switches to open-loop, decelerates the motor in open-loop, crosses zero speed, and
accelerates in the forward direction in open-loop before entering closed loop operation
after motor speed is sufficiently high.
HIZ_EN JudgementThe MSS checks to determine whether the coast (Hi-Z) function is enabled (HIZ_EN =1).
If the coast function is enabled, the MSS advances to the coast routine. If the coast
function is disabled, the MSS advances to the BRAKE_EN judgement.
Coast (Hi-Z) RoutineThe device coasts the motor by turning OFF all six MOSFETs for a certain time
configured by HIZ_TIME.
BRAKE_EN JudgementThe MSS checks to determine whether the brake function is enabled (BRAKE_EN =1). If
the brake function is enabled, the MSS advances to the brake routine. If the brake
function is disabled, the MSS advances to the motor start-up state (see Section 8.3.10.4).
Brake RoutineMCT8316A implements either a time based brake
(duration configured by BRK_TIME) or a current based brake (brake applied till phase
currents < BRK_CURR_THR) based on BRK_CONFIG. Brake is applied either using
high-side or low-side MOSFETs based on BRK_MODE configuration.
Closed Loop StateIn this state, the MCT8316A drives the motor with
trapezoidal control.