ADE7757EB AD [Analog Devices], ADE7757EB Datasheet - Page 4

• Manufacturer Part Number: ADE7757EB
• Description: Evaluation Board Documentation ADE7757 Energy Metering IC
• Manufacturer: AD [Analog Devices]

EVAL-ADE7757EB
than the frequency on F1 and F2. This output can be used
for calibration purposes and is shown connected to a fre-
quency counter via the optoisolator in Figure 6.
At maximum current (25 A), the power seen by the meter
will be 5.5 kW. This will produce a frequency of 0.153 Hz
on F1 and F2 when these outputs are calibrated to
100imp/kWhr (100imp/hr = 0.02777 Hz, 0.02777 x 5.5 =
0.153 Hz). From Table V in the ADE7757 datasheet, the
closest frequency to 0.153 Hz in the half-scale ac inputs
column is for F
tor frequency of 466k Hz. Therefore F
ting S1 = 1 and S0 = 0. The choice of CF frequencies in
this mode (see Table III in the ADE7757 datasheet) are
32 times F1 and 16 times F1. For this example 32 times
F1 is selected by setting SCF = 1.
Since the voltage on Channel 1 is fixed, the only possible
way of calibrating (adjusting) the output frequency in F1
and F2 is by varying the voltage on Channel 2. This is
carried out by varying the attenuation of the line voltage
using the trim pot.
First we can calculate the voltage required in Channel 2 in
order to calibrate the frequency on the logic outputs F1 and F2
to 100imp/kWhr. The ADE7757 datasheet gives the equation
which relates the voltage on Channel 1 and Channel 2 to the
output frequency on F1 and F2.
First a current is selected for calibration, 5 A for example.
This gives a Channel 1 voltage of 400 µ
rms. The on-chip or external reference of 2.5 V is selected
using JP10.
The output frequency at 5 A on F1 and F2 should be
(100imp/kWhr) x 1.1 kW = 0.03055 Hz, where (220 V x
5 A = 1.1 kW).
From Equation 1 the voltage on Channel 2 should be set
to 54.4 mV. The attenuation network as shown in Figure
1 is used to attenuate 220 V to 54.4 mV. R19 = 590 k ,
R20 = 200 k , R22 = 100
However, since the meter is being calibrated at CF and
CF is set to 32 times F1, the voltage on Channel 2 should
be adjusted until CF = 32 x 0.03055 Hz = 0.9776 Hz is
registered on the frequency counter. The counter should
be set up to display the average of ten frequency mea-
surements on CF. This will remove any ripple due to the
instantaneous power signal. See the ADE7757 datasheet
for more details.
JUMPER SELECTION
The ADE7757 evaluation board comes with several
jumper selections that allow the user to exercise all of
the ADE7757 functionality. There are also some options
such as attenuation networks and optically isolated outputs
that allow the ADE7757 to be evaluated under the same
conditions as the end application. Table I outlines all the
jumper options and explains how they are used. Table I
should be used in conjugation with Figure 7, which will
make it easier to locate the jumper in question.
Freq
3
, i.e., 0.18 Hz for a nominal internal oscilla-
515.
84
V
and the trim pot R15 =100 .
V
1
2
PRELIMINARY TECHNICAL DATA
ref
V
2
3
F
1
is selected by set-
4
x 5 A = 2 mV
(1)
–4–
Jumper Option
JP1
JP2
JP3
JP4
JP5
JP6
JP7
Closed
Open
Closed
Open
Closed
Open
Closed
Open
Closed
Open
Closed
Open
Closed
Open
Description
Closing this jumper will short resistor
R16 and connect analog input V1N
directly to SK1B. This has the effect
of removing the antialias filter from
this input.
Antialias filter in input V1N is en-
abled.
Analog input V1N is connected to
analog ground (AGND) via the
antialias filter. This jumper should be
closed if the Channel 1 is used in a
single-ended mode.
When evaluating the ADE7757, Chan-
nel 1 is best used in a differential
mode and this jumper should be left
open. An example is shown in Figure
3. In this example a shunt is used to
sense the current. The shunt can be
referenced to the AGND of the board
by using TP9 as shown.
Closing this jumper will short resistor
R17 and connect analog input V1P
directly to SK1C. This has the effect
of removing the antialias filter from
this input.
Antialias filter in input V1P is enabled.
Analog input V1P is connected to ana-
log ground (AGND) via the antialias
filter.
Normal operation.
Closing this jumper will short resistors
R19 and R20. The analog input V2P is
connected directly to SK2A. This has
the effect of removing the antialias
filter/attenuation network from this
input. Note: if the board is being con-
nected to a high voltage, this jumper
must be left open.
Antialias filter/attenuation network on
the input V2P is enabled.
Analog input V2P is connected to ana-
log ground (AGND) via the antialias
filter/attenuation network. Note: SK2A
is also connected to AGND. Be care-
ful when connecting this input a high
voltage source.
Normal operation.
Closing this jumper will short resistor
R18 and connect analog input V2N
directly to SK2B. This has the effect
of removing the antialias filter/attenua-
tion network from this input.
Antialias filter/attenuation network in
input V2N is enabled.
Table I.
REV. PrF