ADE7757EB AD [Analog Devices], ADE7757EB Datasheet - Page 2

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

EVAL-ADE7757EB
ANALOG INPUTS (SK1 AND SK2)
Voltage and current signals are connected at the screw termi-
nals SK1 and SK2 respectively. All analog input signals are
filtered using the on-board antialias filters before being pre-
sented to the analog inputs of the ADE7757. Some analog
inputs offer additional signal conditioning, e.g., attenuation on
the voltage channel. The default component values included
with the evaluation board are the recommended values to be
used with ADE7757. The user can easily change these compo-
nents, but this is not recommended unless the user is familiar
with sigma-delta converters as well as the criteria used for se-
lecting the analog input filters—see ADE7757 datasheet.
Voltage Input
SK2 is a two-way connection block that can be directly
connected to a high voltage source, e.g., 220 V rms. The
resistor network R15 (trim pot), R19, R20, R21, and R22
make up a very flexible attenuation and calibration net-
work—see schematic. The attenuation network is designed
such that the corner frequency (–3 dB frequency) of the
network matches that of the RC (antialiasing) filters on
the other analog inputs. This is important, because if they
do not match there will be large errors at low power fac-
tors. Figure 1 shows how the attenuation network may be
used with fixed resistors or the trim pot. The trim pot
allows the voltage signal on V2P to be scaled to calibrate
the frequency on CF to some given constant, e.g., 100
imp/kWhr. Some examples are given later.
SK2A
SK2A
Figure 1. Attenuation Network on Channel 2
b. Attenuation Using Fixed Resistors
a. Attenuation Using Trim Pot (R15)
JP6
JP6
JP5
R19
R20
JP5
R19
R20
PRELIMINARY TECHNICAL DATA
R21
C18
C18
R21
R15
R15
JP18
JP18
R22
R22
JP17
JP17
B
A
B
A
V2P
V2P
–2–
EVALUATION BOARD SETUP (ANALOG INPUTS)
Figure 4 shows how the ADE7757 evaluation board can be set
up for a simple evaluation. Two signal generators are used to
provide the sinusoidal (ac) signals for Channel 1 and Channel
2. The user must have some way of phase locking the genera-
tors. Also if the ADE7757 performance-over-power factor is
being evaluated, two separate signal sources will be required.
The generators are shown connected in a single-ended configu-
ration. The grounded analog inputs of Channel 1 and Channel
2 (V1N and V2N) are connected to AGND via an antialias
filter. In Figure 4, analog input V2N is grounded via R21 and
R22. The capacitor C18 is connected in parallel.
If Channel 2 is being used in a single-ended mode of op-
eration, the unused input of the pair should be connected
to analog ground (AGND) via an antialias filter. This is
shown in Figure 2 where V2N is connected to AGND
using jumper JP8.
All passive components (resistors and capacitors) which
make up the attenuation network and antialias filters may
be modified by the user. The components are mounted using
PCB jack sockets for easy removal and replacement of
components.
Current Input
SK1 is a two-way connection block, which allows the
ADE7757 to be connected to a current sensor through one
differential input channel. In this example, we chose a shunt as
the current sensor. Figure 3 shows a typical connection dia-
gram for shunt connection.
Figure 2. Unused Analog Inputs Connected to AGND
SHUNT
Figure 3. Typical Shunt Connection for Channel 1
SK2B
SK1A
SK1B
SK1C
AGND
JP8
R18
JP7
JP2
JP4
R17
R16
JP3
JP1
C19
C17
C16
TP1
TP2
TP5
ADE7757
V1N
V1P
REV. PrF
V2N