ST72141K2 datasheet(40/132 Pages) STMICROELECTRONICS

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ST72141K

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8 ON-CHIP PERIPHERALS

8.1 MOTOR CONTROLLER (MTC)

8.1.1 Introduction

The ST7 Motor Controller (MTC) can be seen as a

Pulse Width Modulator multiplexed on six output

channels,

and

Back

Electromotive

Force

(BEMF) zero-crossing detector for sensorless con-

trol of Permanent Magnet Direct Current (PMDC)

brushless motors.

The MTC is particularly suited to driving synchro-

nous motors and supports operating modes like:

– Commutation step control with motor voltage

regulation and current limitation

– Commutation step control with motor current

regulation, i.e. direct torque control

– Sensor or sensorless motor phase commutation

control

– BEMF zero-crossing detection with high sensitiv-

ity. The integrated phase voltage comparator is

directly referred to the full BEMF voltage without

any attenuation. A BEMF voltage down to

200 mV can be detected, providing high noise

immunity and self-commutated operation in a

large speed range.

– Realtime motor winding demagnetization detec-

tion for fine-tuning the phase voltage masking

time to be applied before BEMF monitoring.

– Automatic and programmable delay between

BEMF zero-crossing detection and motor phase

commutation.

8.1.2 Main Features

Two on-chip analog comparators, one for BEMF

zero-crossing detection with 100 mV hysteresis,

the other for current regulation or limitation

Four selectable reference voltages for the

hysteresis comparator (0.2 V, 0.6 V, 1.2 V,

2.5 V)

8-bit timer (MTIM) with two compare registers

and two capture features

Measurement window generator for BEMF

zero-crossing detection

Auto-calibrated prescaler with 16 division steps

8x8-bit multiplier

Phase input multiplexer

Sophisticated output management:

– The six output channels can be split into two

groups (odd & even).

– The PWM signal can be multiplexed on even,

odd or both groups, alternatively or simultane-

ously.

– The output polarity is programmable channel

by channel.

– An software enabled bit (active low) forces the

outputs in HiZ.

– An “emergency stop” input pin (active low)

asynchronously forces the outputs in HiZ.

Table 10. MTC Registers

8.1.3 Application Example

This example shows a six-step command se-

quence for a 3-phase permanent magnet DC

brushless motor (PMDC motor). Figure 27 shows

the phase steps and voltage, while Table 11

shows the relevant phase configurations.

To run this kind of motor efficiently, an autoswitch-

ing mode has to be used, i.e. the position of the ro-

tor must self-generate the powered winding com-

mutation. The BEMF zero crossing (Z event) on

the non-excited winding is used by the MTC as a

rotor position sensor. The delay between this

event and the commutation is computed by the

MTC and the commutation event Cn is automati-

cally generated after this delay.

After the commutation occurs, the MTC waits until

the winding is completely demagnetized by the

free-wheeling diode: during this phase the winding

is tied to 0V or to the HV high voltage rail and no

BEMF can be read. At the end of this phase a new

BEMF zero-crossing detection is enabled.

The end of demagnetization event (D), is also de-

tected by the MTC or simulated with a timer com-

pare feature when no detection is possible.

Page

MTIM

Timer Counter Register

MZPRV

Capture Zn-1 Register

MZREG

Capture Zn Register

MCOMP Compare Cn+1 Register

MDREG

Demagnetization Register

MWGHT An Weight Register

MPRSR

Prescaler & Sampling Register

MIMR

Interrupt Mask Register

MISR

Interrupt Status Register

MCRA

Control Register A

MCRB

Control Register B

MPHST

Phase State Register

MPAR

Parity Register

MPOL

Polarity Register

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