ST7MC2 datasheet(142/308 Pages) STMICROELECTRONICS

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ST7MC1/ST7MC2

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MOTOR CONTROLLER (Cont’d)

All detections of Zn events are done during a short

measurement window while the high side switch is

turned off. For this reason the PWM signal is ap-

plied on the high side switches.

When the high side switch is off, the high side

winding is tied to 0V by the free-wheeling diode,

the low side winding voltage is also held at 0V by

the low side ON switch and the complete BEMF

voltage is present on the third winding: detection is

then possible.

Table 24. Step Configuration Summary

For a detailed description of the MTC registers,

see Section 10.6.13.

10.6.4 Application Example: AC Induction

Motor Drive

Although the command sequence is rather differ-

ent between a PM BLDC and an AC three-phase

induction motor, the Motor Controller can be con-

figured to generate three-phase sinusoidal voltag-

es.

A timer with three independent PWM channels is

available for this purpose. Based on each of the

PWM reference signal, two complemented PWM

signals with deadtime are generated on the output

pins (6 in total), to drive directly an inverter with tri-

ple half bridge topology.

The variable voltage levels to be applied on the

motor terminals come from continuously varying

duty cycle, from one PWM period to the other (re-

fer to Figure 75 on page 143). The PWM counter

generates a dedicated Update event (U event)

which:

– updates automatically the compare registers set-

ting the duty cycle to avoid time critical issues

and ensure glitchless PWM operation.

– generates a dedicated U interrupt in which the

values for the next coming update event are

loaded in compare preload registers.

The shape of the output voltage (voltage, frequen-

cy, sinewave, trapezoid, ...) is completely man-

aged by the applicative software, in charge of

computing the compare values to be loaded for a

given PWM duty-cycle (refer to Figure 76).

Configuration

Step

Current direction

A to B

A to C

B to C

B to A

C to A

C to B

High side

Low side

OO[5:0] bits in MPHST register

001001

100001

100100

000110

010010

011000

Measurement done on:

MCIC

MCIB

MCIA

MCIC

MCIB

MCIA

IS[1:0] bits in MPHST register

Back EMF shape

Falling

Rising

Falling

Rising

Falling

Rising

CPB bit in MCRB register

(ZVD bit = 0)

010

101

Voltage on measured point at the

start of demagnetization

HDM-SDM bits in MCRB register

PWM side selection to accelerate

demagnetization

Low Side High Side Low Side High Side Low Side High Side

Driver selection to accelerate de-

magnetization

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