ST7MC2 datasheet(156/308 Pages) STMICROELECTRONICS

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MOTOR CONTROLLER (Cont’d)

10.6.6.7 Protection for ZH event detection

To avoid an erroneous detection of a hardware

zero-crossing event, a filter can be enabled by set-

ting the PZ bit in the MCRA register. This filter will

ensure the detection of a ZH event on an edge

transition between D event and ZH event.

Without this protection, ZH event detection is done

directly on the current sample in comparison with

the expected state at the output of the phase com-

parator. For example, if a falling edge transition

(meaning a transition from 1 to 0 at the output of

the phase comparator) is configured for ZH event

through the CPB bit in MCRB register, then, the

state 0 is expected at the comparator output and

once this state is detected, the ZH event is gener-

ated without any verification that the state at the

comparator output of the previous sample was 1.

The purpose of this protection filter is to be sure

that the state of the comparator output at the sam-

ple before was really the opposite of the current

state which is generating the ZH event. With this

filter, the ZH event generation is done on edge

transition level comparison.

This filter is not needed in sensor mode (SR=1)

and for simulated zero-crossing event (ZS) gener-

ation.

When the PZ bit is set, the Z event filter ZEF[3:0] in

the MZFR register is ignored.

Figure 83. Protection of ZH event detection

Sampling clock

Current sample

Previous sample

Phase

Comparator

Falling/Rising Edge

MCRB register MPOL register

CPB* bit

Direct/Filter PZ

MCRA register

bit 1

ZVD bit

V Voltage mode

I Current mode

Rz Rising edge zero-crossing

Fz Falling edge zero-crossing

C Commutation event

Instantaneous

edge

CRz

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