EVAL-ADE7751ZEB Datasheet EVAL-ADE7751ZEB, EVAL-ADE7755ZEB | P1-P3

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EVAL-AD7751/AD7755EB

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Evaluation Board Documentation

AD7751/AD7755 Energy Metering IC

FUNCTIONAL BLOCK DIAGRAM

V1A (AD7751)

NC* (AD7755)

AD7751/

AD7755

V1N (AD7751)

V1N (AD7755)

V1B (AD7751)

V1P (AD7755)

VPLUS

GND

CFOUT

DVDDDGND

V1A/NC*

V1B/V1P

V1N

V2N

V2P

VCC

AD780

74HC08

REVP

FAULT

PROTOTYPE

AREA

H11L1

AVDD

AGND

*NC = NO CONNECT

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

LED Indicators on Logic Outputs for Fault (AD7751

Only), REVP and CF

Optically Isolated Output for Calibration/Test Purposes

External Reference Option Available for Reference

Evaluation

GENERAL DESCRIPTION

The AD7751 and AD7755 are high accuracy energy measurement

ICs. The part specifications surpass the accuracy requirements

as quoted in the IEC1036 standard. The AD7751 incorporates

a novel fault detection scheme that both warns of fault condi-

tions with the logic output FAULT but allows the AD7751 to

continue accurate billing during a fault event. The AD7751

does this by continuously monitoring both the phase and neutral

(return) currents. A fault is indicated when these currents differ

by more than 12.5%. Billing is continued using the larger of the

two currents. The FAULT output is connected to an LED on

the evaluation board.

The AD7751 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 in-

tended to be used for calibration purposes. The evaluation

board allows this logic output to be connected to an LED or

optoisolator. The REVP logic output goes high when negative

real power is detected. This causes an LED on the evaluation

board to switch on.

The AD7751/AD7755 evaluation board can easily be converted

into an energy meter by the addition of a local power supply and

the connection of the appropriate transducers. A large amount

of prototype area is made available on the evaluation board for

this purpose.

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EVAL-AD7751/AD7755EB

–2–

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 AD7751 or AD7755. Some analog inputs

offer additional signal conditioning, e.g., attenuation on the

voltage channel. The default component values shipped with

the evaluation board are the recommended values to be used

with the AD7751 and AD7755. The user can easily change

these components, however this is not recommended unless the

user is familiar with sigma-delta converters and also the criteria

used for selecting the analog input filters—see AD7751 and

AD7755 data sheets.

Voltage Input

SK1 is a two-way connection block that can be directly con-

nected to a high voltage source, e.g., 220 V rms. The resistor

network R53, R54, R55, R56 and R31 make up a very flexible

attenuation and calibration network—see schematic. The attenua-

tion 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., 3200 imp/kWhr. Some ex-

amples are given later.

JP7

JP8

R53

C53

R31

R54

R56

JP52

JP51

SK1A

V2P

R55

a. Attenuation Using Trim Pot (R31)

JP7

JP8

R53

C53

R31

R54

R56

JP52

JP51

SK1A

V2P

R55

b. Attenuation Using Fixed Resistors

Figure 1. Attenuation Network on Channel 2

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 JP10.

JP10

R57

C54

TP5

V2N

JP9

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 at mounted using PCB jack sockets

which allow for easy removal and replacement of components.

Current Input

SK2 is a three-way connection block which allows the AD7751/

AD7755 to be connected to a current transducer. The AD7751

has three inputs which are used with two current transducers,

e.g., two CTs (current transformers). The AD7755 has one

differential input channel for connection to the current trans-

ducer, i.e., two inputs. When using the AD7755 in the evalua-

tion board the input SK2A is not used. PCB jack sockets allow

CT burden resistors to be placed on the evaluation board at

positions SH1 and SH2. Figures 3 and 4 show some typical

connection diagrams for CT and shunt connection.

SK2A

SK2B

SK2C

V1A

V1B

V1N

JP1

JP2

JP3

JP4

JP5

R50

R51

R52

C50

C51

TP2

AD7751

BURDEN RESISTORS

C52

SH1

SH2

TP1

TP3

Figure 3. Typical Connection for Channel 1 of the AD7751

SHUNT

TP11

AGND

NC = NO CONNECT

SK2B

SK2C

V1P

V1N

JP1

JP2

JP3

JP4

JP5

R50

R51

R52

C50

C51

TP2

AD7755

C52

SH1

SH2

TP1

TP3

Figure 4. Typical Connection for Channel 1 of the AD7755

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EVAL-AD7751/AD7755EB

–3–

AD7751/AD7755 EVALUATION BOARD SETUP

Figure 5 shows how the AD7751/AD7755 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

generators. This will ensure that the sinusoidal signals remain in

phase. Also if the AD7751 and AD7755 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 5, analog input V2N is grounded via

R55 and R56. The capacitor C53 is connected in parallel.

SK2B

SK2C

V1B

C50

C51

TP2

C52

TP1

TP3

50Hz

200mV

V1N

V1A

SK2A

JP8

C53

R54

JP9

R57

TP4

C54

TP5

JP1

JP2

R50

JP7

R53

JP3

JP4

R51

JP5

JP6

R52

R31

JP52

JP51

R55

R56

SH2

SH1

JP50

JP11

JP10

SK1A

SK1B

50Hz

200mV

V2P

V2N

Figure 5. Typical Connection for Analog Inputs

LOGIC OUTPUTS

AD7751 and AD7755 provide the active power information in

the form of an output frequency. The three frequency outputs

are F1, F2 and CF. Consult the AD7751 and AD7755 data

sheets 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 VCC (SK4A) and may

be connected to either the AD7751/AD7755 supply using

jumper JP21, or to its own supply.

The logic output CF can be directly connected to an LED using

JP19 (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 con-

nection diagram for this isolated output is shown in Figure 6.

VPLUS

GND

CFOUT

SK5B

SK5C

SK5A

H11L1

JP19

R20

R23

R22

5V–12V

COUNTER

Figure 6. Typical Connection for Opto Output

The logic output REVP indicates negative power measurement.

Since the frequency outputs can only convey magnitude infor-

mation, the sign of the power calculation is given by the REVP

logic output. For more information regarding this output see the

AD7751/AD7755 data sheet. This output is connected to an

LED on the evaluation board. The LED will be illuminated if

negative power is detected.

The AD7751 also has a logic output called FAULT. This out-

put goes active when the signal levels on V1A and V1B differ by

more than 12.5% (see Figure 3). This output is also connected

to an LED on the evaluation board. Jumper J22 should be open

when evaluating the AD7751.

All logic outputs can be monitored via test points 6 to 10 (TP6

to TP10). These test points provide easy access for scope probes

and meter probes.

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EVAL-ADE7751ZEB

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