ST72141K2 datasheet(47/132 Pages) STMICROELECTRONICS

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ST72141K

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MOTOR CONTROLLER (Cont’d)

Demagnetization (D) Event

At the end of the demagnetization phase, current

no longer goes through the free-wheeling diodes.

The voltage on the non-excited winding terminal

goes from one of the power rail voltages to the

common star connection voltage plus the BEMF

voltage. In some cases (if the BEMF voltage is

positive and the free-wheeling diodes are at

ground for example) this end of demagnetization

can be seen as a voltage edge on the selected

MCIx input and it is called a hardware demagneti-

zation event DH. See Table 12.

If enabled by the HDM bit in the MCRB register,

the current value of the MTIM timer is captured in

to be able to simulate the demagnetization phase

for the next steps.

When enabled by the SDM bit in the MCRB regis-

ter, demagnetization can also be simulated by

comparing the MTIM timer with the MDREG regis-

ter. This kind of demagnetization is called software

demagnetization DS.

If the HDM and SDM bits are both set, the first

event that occurs, triggers a demagnetization

event. For this to work correctly, a DS event must

not precede a DH event because the latter could

be detected as a Z event.

Software demagnetization can also be always

used if the HDM bit is reset and the SDM bit is set.

This mode works as a programmable masking

time between the C and Z events. To drive the mo-

tor securely, the masking time must be always

greater than the real demagnetization time in order

to avoid a spurious Z event.

When an event occurs, (either DH or DS) the DI bit

in the MISR register is set and an interrupt request

is generated if the DIM bit of register MIMR is set.

Warning 1: Due to the alternate automatic capture

and compare of the MTIM timer with MDREG reg-

ister by DH and DS events, the MDREG register

should be manipulated with special care.

Warning 2: To avoid a system stop, the value writ-

ten to the MDREG register in Soft Demagnetiza-

tion Mode (SDM = 1) should always be:

– Greater than the MCOMP value of the commuta-

tion before the related demagnetization

– Greater than the value in the MTIM counter at

that moment (when writing to the MDREG regis-

ter).

Figure 30. D Event Generation Mechanism

MTIM [8-bit Up Counter]§

MDREG [Dn]

Compare

HDM bit

D = DH & HDM bit + DS & SDM bit

SDM bit

F(x)

§ Register updated on R event

SDM bit

HDMn bit*

20 µs / C

CPBn bit*

DS,H

Sample

To Z event detection

SR bit

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

To interrupt generator

MCRA Register

MCRB Register

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