STPMC1 datasheet(24/77 Pages) STMICROELECTRONICS

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Theory of operation

STPMC1

24/77

Doc ID 15728 Rev 6

The

ZCR signal is a 3-phase voltage zero cross signal. It is the result of a XNOR of the ZCR

of each phase. The

ZCR of each of the three-phases is a 100 Hz signal, so a 3-phase ZCR

is 300 Hz signal. The

ZCR signal is available on the MOP pin only when the STPMC1 works

as a peripheral with the configuration bit APL=0.

9.6

Period and line voltage measurement (status bits:

LIN, BFR,

LOW, BFF)

From voltage channels, a base frequency signal

LIN is obtained, which is high when the line

voltage is rising and it is low when the line voltage is falling, so that,

LIN signal represents

the sign of dv/dt. With further elaboration, the

ZCR signal is also produced.

A period meter, which is counting up pulses of fMCLK/8 reference signal, measures the

period of voltage channel base frequency and checks if the voltage signal frequency is in the

band going from fMCLK/(2

18 - 23) ≈ fMCLK/218 to fMCLK/216.

This is done, phase by phase, by means of the signal

LIN, which trailing edge is extracted

and it is used to reset the period meter.

If the counted number of fMCLK/8 pulses between two trailing edges of LIN is higher than the

218 equivalent pulses or if the counting is never stopped (no more

LIN trailing edge), the

base frequency exceeds the lower limit and an error flag

BFR is set. This error flag is part of

the 8-bit status byte of each phase (see

Table 32).

Figure 9.

ZCR signal

Table 13.

Good frequency ranges for different clock source values

fXTAL

fMCLK

freq. min. = fMCLK/2

freq. max. = fMCLK/2

4.194 MHz

8.389 MHz

32.0 Hz

128.0 Hz

4.915 MHz

9.830 MHz

37.5 Hz

150.0 Hz

8.192 MHz

31.3 Hz

125.0 Hz

9.830 MHz

37.5 Hz

150.0 Hz

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