ADE7752 Analog Devices, ADE7752 Datasheet - Page 8

• Manufacturer Part Number: ADE7752
• Description: Three Phase Energy Metering IC with Pulse Output
• Manufacturer: Analog Devices

TRANSFER FUNCTION
Frequency Outputs F1 and F2
The ADE7752 calculates the product of six voltage signals
(on Current channel and Voltage channel) and then low-pass
filters this product to extract real power information. This
real power information is then converted to a frequency. The
frequency information is output on F1 and F2 in the form of
active high pulses. The pulse rate at these outputs is relatively
low, e.g., 0.08 Hz maximum for AC signals with SCF = S0
= S1 = 1—see Table III. This means that the frequency at
these outputs is generated from real power information
accumulated over a relatively long period of time. The result
is an output frequency that is proportional to the average real
power. The averaging of the real power signal is implicit to
the digital-to-frequency conversion. The output frequency or
pulse rate is related to the input voltage signals by the
following equation.
where:
Freq
V
I
V
F
SCF
NOTE
*F
A
CLKIN frequency is altered.
1–5
AN
REF
, I
1–5
1
0
-
-
-
B
, V
is a binary fraction of the master clock and therefore will vary if the specified
and I
Freq
BN
=
=
C
and V
S1
1
1
1
0
0
=
109
Table II. F
= Output frequency on F1 and F2 (Hz)
age channels (volts)
= Differential rms voltage signal on Current
channels (volts)
The reference voltage (2.5 V ± 8%) (volts)
One of five possible frequencies selected by
using the logic inputs SCF, S0 and S1—see
Table II.
CN
2 .
×
= Differential rms voltage signal on Volt-
S0
(
V
1
1
0
1
0
AN
1–5
×
I
A
Frequency Selection
+
PRELIMINARY TECHNICAL DATA
F
V
0.596
76.3
19.07
4.77
1.19
V
1–5
BN
REF
×
(Hz)
2
I
B
+
V
CN
XTAL/CLKIN*
10 MHz/2
10 MHz/2
10 MHz/2
10 MHz/2
10 MHz/2
×
I
C
)
×
F
1
−
5
24
17
19
21
23
– 8 –
Example 1
Thus if full-scale differential DC voltages of +125 mV and –
125 mV are applied to VA, VB, VC, IA, IB and IC respec-
tively (125 mV is the maximum differential voltage that
can be connected to Current and Voltage channels), the
expected output frequency is calculated as follows:
F
V
V
Example 2
In this example, with AC voltages of ±500 mV peak ap-
plied to the Voltage channels and Current channels, the
expected output frequency is calculated as follows:
F
V
V
As can be seen from these two example calculations, the
maximum output frequency for AC inputs is always half of
that for DC input signals. The maximum frequency depends
also on the number of phases connected to the ADE7752. In
a 3-phase 3-wire delta service the maximum output frequency
is different from the maximum output frequency in a 3-phase
4-wire Wye service. The reason is that there are only 2 phases
connected to the analog inputs but also that in a delta service,
the Current channel input and Voltage channel input of the
same phase are not in phase in normal operation.
Example 3
In this example, the ADE7752 is connected to a 3-phase 3-
wire delta service as shown in Figure 14. The total real energy
calculation processed in the ADE7752 can be expressed as:
Where V
phase A, B and C. I
on phase A and B.
As the voltage and current inputs respect Equations 5 and 6,
the Total Real Energy (P) is:
Total
1–5
REF
1–5
REF
AN
AN
Freq
Freq
= V
= V
Re
= 0.596 Hz, SCF = S0 = S1 = 1
= +125 mV dc = 0.125 V (rms of dc = dc)
= 2.5 V (nominal reference value).
= 125 mV peak AC = 0.125/
BN
BN
= 0.596 Hz, SCF = S0 = S1 = 1
= 2.5 V (nominal reference value).
A
=
al
=
, V
3
= V
NOTE: If the on-chip reference is used, actual
output frequencies may vary from device to device
due to reference tolerance of ±8%.
= V
NOTE: If the on-chip reference is used, actual
output frequencies may vary from device to device
due to reference tolerance of ±8%.
3
Energy
×
B
×
109
CN
CN
and V
109
= IA = IB = IC
= IA = IB = IC
2 .
2 .
A
=
×
C
and I
×
(
V
. 0
. 0
represent respectively the voltage on
A
125
2
−
125
×
V
B
2
C
represent respectively the current
5 .
×
)
×
2
×
. 0
2
. 0
×
I
125
A
125
2
+
5 .
(
2
V
×
×
B
. 0
2
. 0
−
596
596
volts rms
V
C
REV. PrB 08/01
)
×
=
=
I
. 0
B
. 0
488
24
Hz
Hz