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ADE7751

Energy Metering IC with On-Chip Fault Detection

Analog Devices 

PRELIMINARY TECHNICAL DATA

ADE7751

Using Equations 2 and 3, the real power P can be expressed in

terms of its fundamental real power (P1) and harmonic real

power (PH).

P = P1 + PH

where:

P1 = V1 × I1 cos(φ1)

φ1 = α1 – β1

(4)

∞

and PH = ∑ Vh × Ih × cos(φh )

(5)

h≠1

φh = αh – βh

As shown in Equation 5 above, a harmonic real power compo-

nent is generated for every harmonic, provided that harmonic is

present in both the voltage and current waveforms. The power

factor calculation has been shown previously to be accurate in

the case of a pure sinusoid, therefore the harmonic real power

must also correctly account for the 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 a master clock frequency of 3.5795 MHz.

ANALOG INPUTS

Channel V2 (Voltage Channel)

The output of the line voltage transducer is connected to the

ADE7751 at this analog input. Channel V2 is a fully differen-

tial voltage input. The maximum peak differential signal on

Channel 2 is ± 660 mV. Figure 4 illustrates the maximum

signal levels that can be connected to the ADE7751 Channel 2.

V2

+600mV

VCM

–600mV

DIFFERENTIAL INPUT

؎600mV MAX PEAK

COMMON MODE

؎100mV MAX

V2P

V2 V2N

VCM

AGND

Figure 4. Maximum Signal Levels, Channel 2

Channel 2 must be driven from a common-mode voltage, i.e.,

the differential voltage signal on the input must be referenced to

a common mode (usually AGND). The analog inputs of the

ADE7751 can be driven with common-mode voltages of up to

100 mV with respect to AGND. However, best results are

achieved using a common mode equal to AGND.

Channel V1 (Current Channel)

The voltage outputs from the current transducers are connected

to the ADE7751 here. Channel V1 has two voltage inputs, namely

V1A and V1B. These inputs are fully differential with respect to

V1N. However, at any one time, only one is selected to perform

the power calculation—see Fault Detection section.

The analog inputs V1A, V1B, and V1N have the same maximum

signal level restrictions as V2P and V2N. However, Channel 1

has a programmable gain amplifier (PGA) with user-selectable

gains of 1, 2, 8, or 16—see Table I. These gains facilitate easy

transducer interfacing.

Figure 5 illustrates the maximum signal levels on V1A, V1B,

and V1N. The maximum differential voltage is ± 660 mV divided

by the gain selection. Again, the differential voltage signal on the

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

maximum common-mode signal is ±100 mV as shown in Figure 5.

V1A, V1B

+660mV

GAIN

VCM

–660mV

GAIN

DIFFERENTIAL INPUT A

؎660mV/GAIN MAX PEAK

COMMON MODE

؎100mV MAX

VCM

AGND

DIFFERENTIAL INPUT B

؎660mV/GAIN MAX PEAK

V1A

V1

V1N

V1

V1B

Figure 5. Maximum Signal Levels, Channel 1

Table I.

G1

G0

0

0

0

1

1

0

1

1

Gain

1

2

8

16

Maximum

Differential Signal

± 660 mV

± 330 mV

± 82 mV

± 41 mV

Typical Connection Diagrams

Figure 6 shows a typical connection diagram for Channel V1.

Here the analog inputs are being used to monitor both the

phase and neutral currents. Because of the large potential

difference between the phase and neutral, two CTs (current

transformers) must be used to provide the isolation. Notice

both CTs are referenced to AGND (analog ground), hence

the common-mode voltage is 0 V. The CT turns ratio and

burden resistor (Rb) are selected to give a peak differential

voltage of ± 660 mV/gain.

CT

Rf

V1A

IP

IN

AGND

Rb

؎660mV

GAIN

؎660mV

Rb

GAIN

Cf

V1N

Cf

CT

PHASE NEUTRAL

Rf

V1B

Figure 6. Typical Connection for Channel 1

REV. PrA

–11–

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