CS5490 datasheet(19/57 Pages) CIRRUS

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CS5490

DS982F3

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 6.6.56 on page 51). 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 period. Note

that the CS5490 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 CS5490 provides an independent energy pulse

generation (EPG) block in order to output active,

reactive, and apparent energy pulses on the digital

output pin (DO). 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 10.

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)

If |VPEAK|

VZXLEVEL, then voltage zero-crossing detection is disabled.

If |IPEAK|

IZXLEVEL, then current zero-crossing detection is disabled.

Figure 9. Zero-crossing Level and Zero-crossing Output on DO

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