ST72141K datasheet(49/132 Pages) STMICROELECTRONICS

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ST72141K

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MOTOR CONTROLLER (Cont’d)

BEMF Zero Crossing (Z) Event

When both C and D events have occurred, the

PWM may be switched to another group of outputs

(depending on the OS[2:0] bits in the MCRB regis-

ter) and the real BEMF zero crossing sampling can

start (see Figure 32).

A BEMF voltage is present on the non-powered

terminal but referred to common star connection of

the motor whose voltage is equal to VDD/2.

When a winding is free-wheeling (during PWM off-

time) its terminal voltage changes to the other

power rail voltage, that means if the PWM is ap-

plied on the high side driver, free-wheeling will be

done through the high side diode and the terminal

will be 0V.

This is used to force the common star connection

to 0V in order to read the BEMF referred to the

ground terminal.

Consequently, BEMF reading (i.e. comparison

with a voltage close to 0V) can only be done when

the PWM is applied on the high side drivers.

For this reason the MTC outputs can be split in two

groups called ODD and EVEN and the BEMF

reading will be done only when PWM is applied on

one of these two groups. The REO bit in the MPAR

BEMF sensing (high side group)

Refer to Table 15 for an overview of when a BEMF

can be read depending on REO bit, PWM mode

and function mode of peripheral.

Depending on the edge and level selection (ZVD

and CPB) bits and when PWM is applied on the

correct group, a BEMF zero crossing detection

sets the ZI bit in the MISR register and generates

an interrupt if the ZIM bit is set.

The Z event also triggers some timer/multiplier op-

erations, for more details see Section 8.1.4.2

Figure 31. Sampling and Zero Crossing Blocks

Output of hysteresis comparator

16-bit Timer PWM

Sampling frequency

V0C1 bit

Freq. (T=1.25us) for Demagnetization and Sensor

Sample

DS,H

µs / D

REO bit

DS,H

Sample

SR bit

To D detection

ZVD bit

CPBn bit*

* = Preload register, changes taken into account at next C event.

MCRA Register

MPAR Register

MCRB Register MPAR Register

MCRA Register

Reg

DS,H

events:

Commutation

BEFM Zero-crossing

End Of Demagnetization

Emergency Stop

Notes:

Updated/Shifted on R

Ratio Updated (+1 or -1)

Multiplier Overflow

R+/-

Current Mode

Voltage Mode

Regn

Updated with Regn+1 on C

Branch taken after C event

Branch taken after D event

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