PRELIMINARY TECHNICAL DATA

REV. PrF

EVAL-ADE7757EB

–4–

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

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.

ref

V

F

V

V

Freq

2

4

1

2

1

84

515

−

×

×

×

=

.

(1)

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 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.

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 con-

nected 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 care-

ful 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/attenua-

tion network from this input.

Open

Antialias filter/attenuation network in

input V2N is enabled.