AN2009 datasheet(34/39 Pages) STMICROELECTRONICS

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PWM MANAGEMENT FOR 3-PHASE BLDC MOTOR DRIVES USING THE ST7MC

7.3 REGISTERS CONFIGURATION TO ACCELERATE THE DEMAGNETIZATION.

The ST7MC allows you to program different PWM configurations in sensorless mode. In

sensor mode, the demagnetization event is useless as the feedback information is not read

from the windings.

In order to minimize the demagnetization time in sensorless mode, the ST7MC allows you to

modify the PWM direction between the step commutation and the end of demagnetization.

In sensorless mode the OS2 bit in register MCRB enables the PWM on the high side or low

side channels between the commutation and the demagnetization event.

Table 3. OS bits in MCRB register

D event: Demagnetization

C event: Commutation

Z event: BEMF zero voltage crossing event

OS2 bit

PWM after C and

before D

OS1 bit

PWM after D and

before Z

OS0

PWM after Z and

before next C

On High Channels

On high

channels

On low

channels

On Low Channels

On high

channels

On low

channels

On Low Channels

On High Channels

On high

channels

On low

channels

On Low Channels

On high

channels

On low

channels

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