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

Table 2. off time table

4.3 SUMMARY VOLTAGE/CURRENT MODE

In voltage mode, the 12-bit timer PWM signal (compare U register) gives the voltage to be ap-

plied to the motor. This PWM signal is applied to the switches. The internal clock is not used

in this mode.

A current limitation is implemented in voltage mode. The current limitation can be set by an ex-

ternal divider resistor or by an other PWM signal filtered.

In current mode, the 12-bit timer PWM signal gives the reference current to be applied to the

motor. This signal has to be filtered by an external RC. The internal clock is used and the

PWM signal from the internal clock is applied to the switches.

In current mode, the current is regulated by comparing the reference current and the feedback

current from the motor.

OT3

OT2

OT1

OT0

Off Time sensorless

mode (SR=0)

(DS[3:0]=0)

Sensor Mode (SR=1) or sampling

during ON time in sensorless

(SPLG =1 and/or DS[3:0] bits)

2.5 µs

No minimum off time

5 µs

7.5 µs

10 µs

12.5 µs

15 µs

17.5 µs

20 µs

22.5 µs

25 µs

27.5 µs

30 µs

32.5 µs

35 µs

37.5 µs

40 µs

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