–9–

PRELIMINARY TECHNICAL DATA

REV. PrC.

ADE7757

Using Equations 1 and 2, the real power P can be ex-

H

1

P

P

P

+

=

where:

1

1

1

1

1

1

1

cos

I

V

P

β

−

α

=

φ

φ

×

=

(3)

and

h

h

h

1

h

h

h

h

H

cos

I

V

P

β

−

α

=

φ

φ

×

=

∑

∞

≠

(4)

As can be seen from Equation 4 above, a harmonic real

power component is generated for every harmonic, pro-

vided that harmonic is present in both the voltage and

current waveforms. The power factor calculation has pre-

viously been shown to be accurate in the case of a pure

sinusoid, therefore the harmonic real power must also

correctly account for power factor since it is made up of a

series of pure sinusoids.

Note that the input bandwidth of the analog inputs is

14 kHz with.

ANALOG INPUTS

Channel V1 (Current Channel )

The voltage output from the current sensor is connected to the

ADE7757 here. Channel V1 is a fully differential voltage input.

V1P is the positive input with respect to V1N.

The maximum peak differential signal on Channel V1 should

be less than ±30 mV (21 mV rms for a pure sinusoidal signal)

for specified operation.

DIFFERENTIAL INPUT

±30mV MAX PEAK

+30mV

AGND

V1

V1P

-30mV

COMMON-MODE

±6.25mV MAX

V1N

V1

Figure 13. Maximum Signal Levels, Channel V1

The diagram in Figure 13 illustrates the maximum signal

levels on V1P and V1N. The maximum differential voltage

is ±30 mV. The differential voltage signal on the inputs

must be referenced to a common mode, e.g. AGND. The

maximum common mode signal is ±6.25 mV as shown in

Figure 13.

Channel V2 (Voltage Channel )

The output of the line voltage sensor is connected to the

ADE7757 at this analog input. Channel V2 is a fully differen-

tial voltage input with maximum peak differential signal

of ±165 mV. Figure 14 illustrates the maximum signal

levels that can be connected to the ADE7757 Channel V2.

DIFFERENTIAL INPUT

±165mV MAX PEAK

+165mV

AGND

V2

V2P

-165mV

COMMON-MODE

±25mV MAX

V2N

V2

Figure 14. Maximum Signal Levels, Channel V2

Channel V2 is usually driven from a common-mode volt-

age, i.e., the differential voltage signal on the input is

referenced to a common mode (usually AGND). The

analog inputs of the ADE7757 can be driven with com-

mon-mode voltages of up to 25 mV with respect to

AGND. However best results are achieved using a com-

mon mode equal to AGND.

Typical Connection Diagrams

Figure 15 shows a typical connection diagram for Channel V1.

A shunt is the current sensor selected for this example because of

its low cost compared to other current sensors such as the CT

(current transformer). This IC is ideal for low current

meters.

V1P

AGND

Rf

Rf

SHUNT

V1N

Cf

Cf

PHASE

NEUTRAL

Figure 15. Typical Connection for Channel V1

Figure 16 shows a typical connection for Channel V2.

Typically, ADE7757 is biased around the neutral wire,

and a resistor divider is used to provide a voltage signal

that is proportional to the line voltage. Adjusting the ratio

of Ra, Rb and VR is also a convenient way of carrying out

a gain calibration on a meter.

Ra*

Rb*

VR*

V2P

Rf

NEUTRAL

PHASE

V2N

Cf

Cf

*Ra >> Rf + VR

*Rb + VR = Rf

Figure 16. Typical Connections for Channel V2