ADE5166 datasheet(51/148 Pages) AD

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ADE5166/ADE5169

Rev. 0 | Page 51 of 148

PGA1

IP/IPA

ADC 1

HPF

PGA2

ADC 2

LPF2

60Hz

0.1°

CHANNEL 2 DELAY

REDUCED BY 4.48µs

(0.1°LEAD AT 60Hz)

0x0B IN PHCAL[7:0]

PHCAL[7:0]

–231.93µs TO +48.83µs

60Hz

DELAY BLOCK

1.22µs/LSB

Figure 55. Phase Calibration

RMS CALCULATION

The root mean square (rms) value of a continuous signal V(t) is

defined as

∫

rms

)

(

()

(1)

For time sampling signals, rms calculation involves squaring the

signal, taking the average, and obtaining the square root. The

ADE5166/ADE5169 implement this method by serially squaring

the input, averaging them, and then taking the square root of

the average. The averaging part of this signal processing is done

by implementing a low-pass filter (LPF3 in Figure 56, Figure 57,

and Figure 58).

This LPF has a −3 dB cutoff frequency of 2 Hz when MCLK =

4.096 MHz.

)

sin(

()

−

cos

)

(

(2)

where V is the rms voltage.

(3)

When this signal goes through LPF3, the cos(2ωt) term is attenu-

ated and only the dc term, Vrms2 (shown as V2 in Figure 56), goes

through.

LPF3

INPUT

V2 (t) = V2 –V2 cos(2ωt)

V2 (t) = V2

V(t) = √2 × V sin(ωt)

Figure 56. RMS Signal Processing

The Irms signal can be read from the waveform register by set-

ting the WAVMODE register (Address 0x0D) and setting the

WFSM bit (Bit 5) in the Interrupt Enable 3 SFR (MIRQENH,

Address 0xDB). Like the current and voltage channels waveform

sampling modes, the waveform data is available at sample rates of

25.6 kSPS, 12.8 kSPS, 6.4 kSPS, and 3.2 kSPS.

It is important to note that when the current input is larger than

40% of full scale, the Irms waveform sample register does not

represent the true processed rms value. The rms value processed

with this level of input is larger than the 24-bit read by the wave-

form register, making the value read truncated on the high end.

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