ADE7753ARS datasheet(32/60 Pages) AD

32 / 60 page

ADE7753

Rev. C | Page 32 of 60

From Equation 19 it can be seen that there is a small ripple in

the energy calculation due to a sin(2 ωt) component. This is

shown graphically in Figure 68. The active energy calculation is

shown by the dashed straight line and is equal to V × I × t. The

sinusoidal ripple in the active energy calculation is also shown.

Since the average value of a sinusoid is 0, this ripple does not

contribute to the energy calculation over time. However, the

ripple can be observed in the frequency output, especially at

higher output frequencies. The ripple gets larger as a percentage

of the frequency at larger loads and higher output frequencies.

The reason is simply that at higher output frequencies the

integration or averaging time in the energy-to-frequency

conversion process is shorter. As a consequence, some of the

sinusoidal ripple is observable in the frequency output. Choosing

a lower output frequency at CF for calibration can significantly

reduce the ripple. Also, averaging the output frequency by using

a longer gate time for the counter achieves the same results.

–

sin(4

×π×f

L×t)

×π×f

L(1+2×fL/8. 9Hz )

E(t)

Vlt

02875-0-067

Figure 68. Output Frequency Ripple

WDIV[7:0]

APOS[15:0]

WGAIN[11:0]

LPF1

LAENERGY [23:0]

ACCUMULATE ACTIVE

ENERGY IN INTERNAL

THE LAENERGY REGISTER

AT THE END OF LINECYC

LINE CYCLES

OUTPUT

FROM

LPF2

FROM

CHANNEL 2

ADC

LINECYC [15:0]

02875-0-068

ZERO CROSS

DETECTION

CALIBRATION

CONTROL

Figure 69. Energy Calculation Line Cycle Energy Accumulation Mode

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