PRELIMINARY TECHNICAL DATA

REV. PrF

EVAL-ADE7757EB

–2–

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.

JP5

JP6

R19

C18

R15

R20

R22

JP18

A

B

JP17

SK2A

V2P

R21

a. Attenuation Using Trim Pot (R15)

JP5

JP6

R19

C18

R15

R20

R22

JP18

A

B

JP17

SK2A

V2P

R21

b. Attenuation Using Fixed Resistors

Figure 1. Attenuation Network on Channel 2

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.

JP8

R18

C19

TP5

V2N

JP7

SK2B

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 dia-

gram for shunt connection.

SHUNT

AGND

SK1A

SK1B

ADE7757

JP1

JP2

R16

C16

TP1

V1P

JP3

R17

C17

TP2

JP4

V1N

SK1C

Figure 3. Typical Shunt Connection for Channel 1

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.