CS5480 datasheet(22/70 Pages) CIRRUS

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CS5480

DS980F3

5.4 Line Frequency Measurement

If the Automatic Frequency Calculation (AFC) bit in the

Config2 register is set, the line frequency measurement

on a voltage channel will be enabled. The line frequency

measurement is based on a number of voltage channel

zero crossings. This number is 100 by default and

configurable through the ZXNUM register (see section

6.6.7 on page 43). The Epsilon register will be updated

automatically with the line frequency information. The

Frequency Update (FUP) bit in the Status0 interrupt

status register is set when the frequency calculation is

completed. When the line frequency is 50Hz and the

ZXNUM register is 100, the Epsilon register is updated

every one second with a resolution of less than 0.1%. A

bigger zero-crossing number in the ZXNUM register will

increase both line frequency measurement resolution

and period. Note that the CS5480 line frequency

measurement function does not support the line

frequency out of the range of 40Hz to 75Hz.

The Epsilon register is also used to set the gain of the

90° phase shift filter used in the quadrature power cal-

culation. The value in the Epsilon register is the ratio of

the line frequency to the output word rate (OWR). For

50Hz line frequency and 4000Hz OWR, Epsilon is

50/4000 (0.0125) (the default). For 60Hz line frequen-

cy, it is 60/4000 (0.015).

VZXLEVEL

IZXLEVEL

If |VPEAK|

> VZXLEVEL, then voltage zero-crossing detection is enabled.

If |IPEAK|

> IZXLEVEL, then current zero-crossing detection is enabled.

Zero-crossing output on DOx pin

Pulse width = 250μs

t), I(t)

DOx

If |VPEAK|

VZXLEVEL, then voltage zero-crossing detection is disabled.

If |IPEAK|

IZXLEVEL, then current zero-crossing detection is disabled.

Figure 13. Zero-crossing Level and Zero-crossing Output on DOx

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