ADE7755ARSRL View Datasheet(PDF) - Analog Devices

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ADE7755ARSRL

Energy Metering IC with Pulse Output

Analog Devices 

PRELIMINARY TECHNICAL DATA

ADE7755

Using Equations 1 and 2, 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

(3)

φ1 = α1 – β1

and:

∞

PH = ∑ Vh × Ih cos φh

h ≠1

(4)

φh = αh – βh

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

component is generated for every harmonic, provided that har-

monic is present in both the voltage and current waveforms.

The power factor calculation has previously been shown 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.

Table I. Gain Selection for Channel 1

Maximum

G1

G0

Gain

Differential Signal

0

0

1

0

1

2

1

0

8

1

1

16

± 470 mV

± 235 mV

± 60 mV

± 30 mV

Channel V2 (Voltage Channel )

The output of the line voltage transducer is connected to the

ADE7755 at this analog input. Channel V2 is a fully differential

voltage input. The maximum peak differential signal on

Channel 2 is ± 660 mV. Figure 5 illustrates the maximum

signal levels that can be connected to the ADE7755 Channel 2.

V2

+660mV

VCM

–660mV

DIFFERENTIAL INPUT

؎660mV MAX PEAK

V2P

V2 V2N

COMMON-MODE

؎100mV MAX

VCM

AGND

ANALOG INPUTS

Channel V1 (Current Channel )

The voltage output from the current transducer is connected to

the ADE7755 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 1 should be

less than ± 470 mV (330 mV rms for a pure sinusoidal signal) for

specified operation. Note that Channel 1 has a programmable

gain amplifier (PGA) with user selectable gain of 1, 2, 8, or 16

(see Table I). These gains facilitate easy transducer interfacing.

V1

+470mV

VCM

–470mV

DIFFERENTIAL INPUT

؎470mV MAX PEAK

COMMON-MODE

؎100mV MAX

V1P

V1 V1N

VCM

AGND

Figure 4. Maximum Signal Levels, Channel 1, Gain = 1

The diagram in Figure 4 illustrates the maximum signal levels

on V1P and V1N. The maximum differential voltage is ±470 mV

divided by the gain selection. 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 4.

Figure 5. 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

ADE7755 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.

Typical Connection Diagrams

Figure 6 shows a typical connection diagram for Channel V1. A

CT (current transformer) is the current transducer selected for this

example. Notice the common-mode voltage for Channel 1 is

AGND and is derived by center tapping the burden resistor to

AGND. This provides the complementary analog input signals

for V1P and V1N. The CT turns ratio and burden resistor Rb

are selected to give a peak differential voltage of ± 470 mV/Gain

at maximum load.

CT

Rb

Rf

؎470mV

GAIN

V1P

Cf

V1N

IP

AGND

PHASE NEUTRAL

Rf

Cf

Figure 6. Typical Connection for Channel 1

REV. PrA

–11–

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