Cirrus Logic CS5480 - Manual (Page 22)

CS5480
22 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 ZX
NUM
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
ZX
NUM
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 ZX
NUM
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).
VZX
LEVEL
IZX
LEVEL
If |V
PEAK
|
> VZX
LEVEL
, then voltage zero-crossing detection is enabled.
If |I
PEAK
|
> IZX
LEVEL
, then current zero-crossing detection is enabled.
Zero-crossing output on DOx pin
Pulse width = 250μs
V( t), I(t)
DOx
t
t
If |V
PEAK
| ” VZX
LEVEL
, then voltage zero-crossing detection is disabled.
If |I
PEAK
| ” IZX
LEVEL
, then current zero-crossing detection is disabled.
Figure 13. Zero-crossing Level and Zero-crossing Output on DOx