Datasheet

ADE7752/ADE7752A
Rev. C | Page 21 of 24
Table 6 shows a complete listing of all maximum output
frequencies when using all three channel inputs.
As the voltage and current inputs respect Equations 5 and 6, the
total real power (P) is
()( )()( )
()
()
⎟
⎠
⎞
⎜
⎝
⎛
+×××
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎟
⎠
⎞
⎜
⎝
⎛
+××−
⎟
⎠
⎞
⎜
⎝
⎛
+××+
×××
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎟
⎠
⎞
⎜
⎝
⎛
+××−××=
−×−+−−=
3
2
cos2
3
4
cos2
3
2
cos2
cos2
3
4
cos2cos2
π
ω
π
ω
π
ω
ω
π
ωω
tI
tVvtV
tI
tVtVP
IIVVIIVVP
lB
lClB
lA
lClA
BNBPCBANAPCA
Table 6. Maximum Output Frequency on F1 and F2
For simplification, assume that ϕ
A
= ϕ
B
= ϕB
C
= 0 and
V
A
= V
B
B = V
C
= V. The preceding equation becomes:
()
()
⎟
⎠
⎞
⎜
⎝
⎛
+×+×
⎟
⎠
⎞
⎜
⎝
⎛
×××+
×
⎟
⎠
⎞
⎜
⎝
⎛
+×
⎟
⎠
⎞
⎜
⎝
⎛
×××=
3
2
cossin
3
sin2
cos
3
2
sin
3
2
sin2
π
tωπtω
π
IV
tω
π
tω
π
IVP
ll
B
ll
A
(9)
P then becomes:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎟
⎠
⎞
⎜
⎝
⎛
++
⎟
⎠
⎞
⎜
⎝
⎛
××+
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎟
⎠
⎞
⎜
⎝
⎛
++
⎟
⎠
⎞
⎜
⎝
⎛
××=
3
2sin
3
sin
3
2
2sin
3
2
sin
π
ω
π
π
ω
π
tIV
tIVP
lBBN
lAAN
(10)
where V
AN
= V × sin(2π/3) and V
BN
= V × sin(π/3).
As the LPF on each channel eliminates the 2ωl component of
the equation, the real power measured by the ADE7752 is
2
3
2
3
××+××=
BBNAAN
IVIVP
If full-scale ac voltage of ±500 mV peak is applied to the voltage
channels and current channels, the expected output frequency
is calculated as follows:
value referencenominal V4.2
0
2
5.0
500
110,60.0
71
=
==
======
====
−
REF
CCN
CBABNAN
V
IV
rmsacpeakIIIVV
SSSCFF
VVm
Hz
Note that if the on-chip reference is used, actual output fre-
quencies may vary from device to device due to reference
tolerance of ±8%.
Hz139.0
2
3
4.222
60.05.05.0181.6
2
2
=×
××
×××
×=Freq
SCF S1 S0
Max Frequency for
AC Inputs (Hz)
Max Frequency for
DC Inputs (Hz)
1.02 0 0 0 0.51
1 0 0 0.48 0.96
0 0 1 2.04 4.09
1 0 1 1.91 3.84
0 1 0 7.67 15.35
1 1 0 7.67 15.35
0 1 1 30.70 61.4
0.48 1 1 1 0.24
FREQUENCY OUTPUT CF
The pulse output calibration frequency (CF) is intended for use
during calibration. The output pulse rate on CF can be up to
160 times the pulse rate on F1 and F2. The lower the F
1–7
frequency selected, the higher the CF scaling.
Table 7 shows
how the two frequencies are related, depending on the states of
the logic inputs S0, S1, and SCF. Because of its relatively high
pulse rate, the frequency at this logic output is proportional to
the instantaneous real power. As with F1 and F2, the frequency
is derived from the output of the low-pass filter after multiplica-
tion. However, because the output frequency is high, this real
power information is accumulated over a much shorter time.
Thus, less averaging is carried out in the digital-to-frequency
conversion. With much less averaging of the real power signal,
the CF output is much more responsive to power fluctuations.
See
Figure 15.
Table 7. Maximum Output Frequency on CF
SCF S1 S0 F
1–7
(Hz) CF Max for AC Signals (Hz)
0 0 0 1.27 160 × F1, F2 = 81.87
1 0 0 1.19 8 × F1, F2 = 3.83
0 0 1 5.09 160 × F1, F2 = 327.46
1 0 1 4.77 16 × F1, F2 = 30.70
0 1 0 19.07 16 × F1, F2 = 122.81
1 1 0 19.07 8 × F1, F2 = 61.40
0 1 1 76.29 8 × F1, F2 = 245.61
1 1 1 0.60 16 × F1, F2 = 3.84