ANALOG DEVICES EVAL-ADE7757EB Service Manual

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PRELIMINARY TECHNICAL DA T A

Evaluation Board Documentation

a

Preliminary Technical Data

FEATURES
Single +5 V Power Supply
Easy Connection of External Transducers via Screw

Terminals

Easy Modification of Signal Conditioning Components

Using PCB Sockets
Trim Pot for Analog Calibration of Meter Constant
Optically Isolated Output for Calibration/Test Purposes
External Reference Option Available for Reference

Evaluation

ADE7757 Energy Metering IC

EVAL-ADE7757EB

GENERAL DESCRIPTION

The ADE7757 is a high accuracy energy measurement IC
with integrated oscillator. The part specifications surpass
the accuracy requirements as quoted in the IEC1036 stan­dard.

The ADE7757 supplies average real power information on the
low frequency outputs F1 and F2. These logic outputs may be
used to directly drive an electromechanical counter or interface
to an MCU. The evaluation board provides screw connectors
for easy connection to an external counter. The CF logic out­put gives instantaneous real power information. This output is
intended to be used for calibration purposes. The evaluation
board allows this logic output to be connected to an LED or
optoisolator.

The ADE7757 evaluation board can easily be converted into
an energy meter by the addition of a local power supply and
the connection of the appropriate current sensor. A large
amount of prototype area is made available on the evaluation
board for this purpose.

V2P

V2N

V1N

V1P

FUNCTIONAL BLOCK DIAGRAM

VCC

AGND

ADE7757

AD780

VDD

74HC08

PROTOTYPE

AREA

DGND

CF

H11L1

F1

F2

VPLUS

CFOUT

VMINUS

REV. PrF

Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, USA
Tel: [phone] www.analog.com
Fax: [phone] © Analog Devices, Inc., June 2002

EVAL-ADE7757EB

PRELIMINAR Y TECHNICAL DA T A

ANALOG INPUTS (SK1 AND SK2)

Voltage and current signals are connected at the screw termi­nals SK1 and SK2 respectively. All analog input signals are
filtered using the on-board antialias filters before being pre­sented 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 compo­nents, but this is not recommended unless the user is familiar
with sigma-delta converters as well as the criteria used for se­lecting 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 net­work—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 fac­tors. 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.

If Channel 2 is being used in a single-ended mode of op­eration, 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.

JP7

SK2B

R18

JP8

TP5

V2N

C19

Figure 2. Unused Analog Inputs Connected to AGND

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 dia­gram for shunt connection.

JP5

SK2A

R19

R20

JP6

JP18

R21

R15

C18

a. Attenuation Using Trim Pot (R15)

JP5

SK2A

JP6

R19

R20

R21

R15

C18

b. Attenuation Using Fixed Resistors

Figure 1. Attenuation Network on Channel 2

JP18

R22

R22

B

JP17

A

JP17

SK1A

SK1B

V2P

B

SHUNT

SK1C

Figure 3. Typical Shunt Connection for Channel 1

AGND

JP2

JP4

JP1

R16

JP3

R17

TP1

C16

TP2

C17

ADE7757

V1N

V1P

EVALUATION BOARD SETUP (ANALOG INPUTS)

Figure 4 shows how the ADE7757 evaluation board can be set

A

V2P

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 genera­tors. 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 configu­ration. 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.

–2–

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PRELIMINARY TECHNICAL DA T A

EVAL-ADE7757EB

JP5

A

50Hz

220V

50Hz

30mV

SK2A

SK2B

SK1A

SK1B

SK1C

R19

R20

JP6

JP8

AGND

C18

JP7

R18

JP2

JP4

JP1

R16

JP3

R17

JP18

R21

R15

R22

JP17

C19

P

TP4

B

N

JP16

P

N

JP9

TP1

C16

TP2

C17

V2P

V2N

TP5

V1N

V1P

Figure 4. Typical Connection for Analog Inputs

LOGIC OUTPUTS

ADE7757 provides the active power information in the
form of an output frequency. The three frequency outputs
are F1, F2 and CF. Consult the datasheet for more infor­mation on these outputs. The logic outputs F1 and F2 are
intended to be used to drive an impulse counter or stepper
motor. The outputs are buffered and available at the con­nector SK6. A stepper motor may be directly connected
here. The power supply for the buffer is +5V (SK4A) and
may be connected to the ADE7757 supply using jumper
JP15, or to its own supply.

The logic output CF can be directly connected to an LED
using JP14 (Position B) or to an optically isolated output (Posi­tion A). By closing Positions A and B, both options are se­lected. The optically isolated output is available at connector
SK5. This isolated output is useful when the evaluation board
is connected directly to a high voltage (e.g., 220 V residential). A
typical connection diagram for this isolated output is shown in
Figure 5.

JP14

B

A

R11

OUTPUT FREQUENCY SELECTION

ADE7757 provides up to four different output frequencies
on F1 and F2. The output frequency selection is made via
the logic inputs S0 and S1—see ADE7757 datasheet. On
the evaluation board these inputs are set by using jumpers
JP12 and JP13. The logic input SCF is set via jumper 11
(JP11). For a full explanation of the ADE7757 output
frequency selection see the datasheet.

INTERNAL CLOCK

The ADE7757’s integrated oscillator serves as the clock
source to the chip. A precise 6.2 k

Ω

resistor with low
tolerance and low drift is used to drive the internal oscilla­tor.

NEUTRAL

SHUNT

5.000V

PHASE

220V

SK1A

SK1B

5A

2mV

SK1C

SK2A

SK2B

LOAD

JP1 = OPEN
JP2 = OPEN
JP3 = OPEN
JP4 = OPEN
JP5 = OPEN
JP6 = OPEN
JP7 = OPEN
JP8 = CLOSED
JP9 = N

SK3A

VDD

AGND

AGND

V1N

V1P

JP5

R19

R20

JP6

C18

JP11 = 1
JP12 = 1
JP13 = 0
JP14 = A,B
JP16 = P
JP17 = A
JP18 = CLOSED
R21 = REMOVED

SK3B

R21

5.000V

JP18

R15

R22

SK5A

SK5B

SK5C

B

JP17

A

TP4

V2

54.5mV

0.9776 Hz

FREQUENCY DISPLAY

100

imp/kWhr

R12

U4

H11L1

VPLUS

CFOUT

VMINUS

R4

R5

SK5A

SK5B

SK5C

+

5V to 12V

COUNTER

Figure 5. Typical Connection for Opto Output

All logic outputs can be monitored via test points 6 to 8
(TP6 to TP8). These test points provide easy access for
scope probes and meter probes.

REV. PrF

Figure 6. ADE7757 Evaluation Board as an Energy Meter

EVALUATION BOARD SET UP AS AN ENERGY
METER

Figure 6 shows a wiring diagram that allows a simple
energy meter to be implemented using the ADE7757
evaluation board. The current transducer used in this ex-

Ω

ample is a 400 µ

shunt. The meter is intended to be used
with a line voltage of 220 V and a maximum current of
25 A. The frequency outputs F1 and F2 can be used to
drive a mechanical counter. These outputs will be cali­brated to provide 100 imp/kWhr. The logic output CF
has an output frequency that can be up to 2048 times higher

–3–

EVAL-ADE7757EB

PRELIMINAR Y TECHNICAL DA T A

than the frequency on F1 and F2. This output can be used
for calibration purposes and is shown connected to a fre­quency 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

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 mea­surements 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.

, i.e., 0.18 Hz for a nominal internal oscilla-

3

84515

.

=

Freq

Ω,

R22 = 100Ω and the trim pot R15 =100Ω.

2

V

is selected by set-

3

×××

FVV

4121

−

ref

Ω

x 5 A = 2 mV

Ω

(1)

,

–4–

Table I.

Jumper Option Description

JP1 Closed 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.

Open Antialias filter in input V1N is en-

abled.

JP2 Closed 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.

Open 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.

JP3 Closed 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.

Open Antialias filter in input V1P is enabled.

JP4 Closed Analog input V1P is connected to ana-

log ground (AGND) via the antialias
filter.

Open Normal operation.

JP5 Closed 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 con­nected to a high voltage, this jumper
must be left open.

Open Antialias filter/attenuation network on

the input V2P is enabled.

JP6 Closed Analog input V2P is connected to ana-

log ground (AGND) via the antialias
filter/attenuation network. Note: SK2A
is also connected to AGND. Be care­ful when connecting this input a high
voltage source.

Open Normal operation.

JP7 Closed Closing this jumper will short resistor

R18 and connect analog input V2N
directly to SK2B. This has the effect
of removing the antialias filter/attenua­tion network from this input.

Open Antialias filter/attenuation network in

input V2N is enabled.

REV. PrF