CS5484 datasheet(22/67 Pages) CIRRUS

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CS5484

DS981F3

5.4 Line Frequency Measurement

If the Automatic Frequency Calculation (AFC) bit in the

Config2 register is set, the line frequency measurement

on the 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 6.6.76 on page 61). 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 larger zero-crossing

number in the ZXNUM register will increase line

frequency measurement resolution and the period. Note

that the CS5484 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

calculation. 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

frequency, it is 60/4000 (0.015).

5.5 Energy Pulse Generation

The CS5484 provides four independent energy pulse

generation blocks (EPG1, EPG2, EPG3, and EPG4) in

order to simultaneously output active, reactive, and

apparent energy pulses on any of the four digital output

pins (DO1, DO2, DO3, and DO4). The energy pulse

frequency is proportional to the magnitude of the power.

The energy pulse output is commonly used as the test

output of a power meter. The host microcontroller can

also use the energy pulses to easily accumulate the

energy. Refer to Figure 14.

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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