MCT8317A datasheet(34/161 Pages) TI1

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BEMF >

RESYNC_MIN_THRESHOLD

Judgement

If motor speed is such that BEMF > RESYNC_MIN_THRESHOLD,

MCT8317A uses the speed and position information from ISD to

transition to the closed loop state (see Section 8.3.9.2 ) directly. If

BEMF < RESYNC_MIN_THRESHOLD, MCT8317A proceeds to BEMF <

STAT_DETECT_THR judgement.

BEMF < STAT_DETECT_THR

Judgement

If motor speed is such that BEMF > STAT_DETECT_THR, MCT8317A

proceeds to motor coast timeout. If BEMF < STAT_DETECT_THR,

MCT8317A proceeds to STAT_BRK_EN judgement.

Motor Coast Timeout

MCT8317A waits for 200000 PWM cycles for the motor to coast down to

a speed where BEMF < STAT_DETECT_THR; after 200000 PWM cycles

lapse in the motor coast state, MCT8317A proceeds to STAT_BRK_EN

judgement irrespective of BEMF. If BEMF < STAT_DETECT_THR during

motor coast before the 200000 cycle timeout, MCT8317A proceeds to

STAT_BRK_EN judgement immediately.

RVS_DR_EN Judgement

The MSS checks to see if the reverse drive function is enabled

(RVS_DR_EN = 1b). If it is enabled, the MSS transitions to check speed

of the motor in reverse direction. If the reverse drive function is not enabled

(RVS_DR_EN = 0b), the MSS advances to the HIZ_EN judgement.

Speed > MIN_DUTY Judgement The MSS checks if the speed (in reverse direction) is higher than the

speed at MIN_DUTY - till the speed (in reverse direction) is higher than

the speed at MIN_DUTY, MSS stays in reverse closed loop deceleration.

When speed (in reverse direction) drops below the speed at MIN_DUTY, the

MSS transitions to reverse open loop deceleration.

Reverse Open Loop

Deceleration and Zero Speed

Crossover

In reverse open loop deceleration, the MCT8317A decelerates the motor

in open-loop till speed reaches zero. At zero speed, direction changes and

MCT8317A begins open loop acceleration.

HIZ_EN Judgement

The MSS checks to determine whether the coast (Hi-Z) function is enabled

(HIZ_EN = 1b). If the coast function is enabled (HIZ_EN = 1b), the MSS

advances to the coast routine. If the coast function is disabled (HIZ_EN =

0b), the MSS advances to the BRAKE_EN judgement.

Coast (Hi-Z) Routine

The device coasts the motor by turning OFF all six MOSFETs for a certain

time configured by HIZ_TIME.

BRAKE_EN Judgement

The MSS checks to determine whether the brake function is enabled

(BRAKE_EN = 1b). If the brake function is enabled (BRAKE_EN = 1b),

the MSS advances to the brake routine. If the brake function is disabled

(BRAKE_EN = 0b), the MSS advances to the motor start-up state (see

Section 8.3.9.4).

Brake Routine

MCT8317A 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. Current based brake is

followed by an additional brake time to ensure the motor is stationary before

start-up; this additional brake time is configured by STARTUP_BRK_TIME.

Brake is applied either using high-side or low-side MOSFETs based on

BRK_MODE configuration.

Closed Loop

In this state, the MCT8317A drives the motor with sensorless trapezoidal

commutation based on either zero cross detection or BEMF integration.

8.3.9.1 Initial Speed Detect (ISD)

The ISD function is used to identify the initial condition of the motor and is enabled by setting ISD_EN to 1b. The

initial speed, position and direction is determined by sampling the phase voltage through the internal ADC. ISD

MCT8317A

SLLSFQ2 – JANUARY 2023

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