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ADE9078

Data Sheet

Rev. 0 | Page 22 of 107

THEORY OF OPERATION

The ADE9078 integrates seven high performance ADCs and a

flexible DSP core. An integrated high end reference ensures low

drift over temperature with a combined drift of less than

±25 ppm/°C maximum for the whole channel including PGA

and ADC.

The ADE9078 is a highly accurate, fully integrated energy

metering device. Interfacing with both CT and Rogowski coil

sensors, the ADE9078 enables users to develop a 3-phase metrology

platform, which achieves high performance for Class 1 through

Class 0.2 meters. See the Measurements (Normal Mode) section

for more information.

Two power modes are provided to enable detection of meter

tampering: PSM2 uses a low power comparator to compare

current channels to a threshold and indicates whether it has

been exceeded on the IRQ0 and IRQ1 outputs; PSM1 enables

fast measurement of current and voltage rms (xVRMS, xIRMS),

active power, and VAR during a tamper. See the Measurements

(PSM1) section and Measurements (PSM2) section for more

information about how to use these modes.

ADC

Overview

The ADE9078 incorporates seven independent, second-order, Σ-Δ

ADCs that sample simultaneously. Each ADC is 24 bits and supports

fully differential and pseudo differential inputs that can go above

and below ground. The ADE9078 includes a low noise, low drift,

internal band gap reference. Set the EXT_REF bit in the CONFIG1

a programmable gain amplifier, which allows a gain of 1, 2, or 4.

The ADCs incorporate proprietary dither techniques to prevent

idle tones at low input levels, extending the accuracy range.

Analog Input Configuration

There is no internal buffering on the device. The impedance of

the ADE9078 depends on the programmable gain selected (see

the Specifications table).

Fully Differential Inputs

The input signals on the IAP, IAN, IBP, IBN, ICP, ICN, VAP, VAN,

VBP, VBN, VCP, and VCN pins must not exceed 0.6 V relative

to AGND, the analog ground reference. The differential full-

scale input range of the ADCs is ±1 V peak (0.707 V rms), and

the maximum allowed common-mode voltage at the ADC pins

must not exceed ±0.1 V.

Figure 30 and Figure 31 show two common types of input

signals for an energy metering application. Figure 30 shows the

maximum input allowed with differential antiphase signals. A

current transformer with center tapped burden resistor generates

differential antiphase signals. Figure 31 shows the maximum

input signal with pseudo differential signals, similar to those

obtained when sensing the mains voltage signal through a

resistive divider or using a Rogowski coil current sensor.

The following conditions must be met for the input signals with

gain = 1:



|IAP, IAN, IBP, IBN, ICP, ICN, VAP, VAN, VBP, VBN, VCP,

and VCN| ≤ 0.6 V peak relative to AGND



|IxP − IxN| ≤ 1 V peak, |VxP − VxN| ≤ 1 V peak

+0.1V

+0.6V

–0.4V

0x0474 E650 =

NOTES

1. x_PCF IS THE INSTANTANEOUS WAVEFORM OBTAINED

AFTER GAIN AND PHASE COMPENSATION.

+74,770,000

0xFB8B 19B0 =

–74,770,000

CHANNEL (x_PCF) WAVEFORM

DATA RANGE WITH x_GAIN = 1

xP INPUT PIN

xM INPUT PIN

+0.1V

+0.6V

–0.4V

Figure 30. Maximum Input Signal with Differential Antiphase Input with

Common-Mode Voltage = 0.1 V, Gain = 1

+0.1V

+0.6V

–0.4V

+0.1V

0x0474 E650 =

+74,770,000

xFB8B 19B0 =

–74,770,000

CHANNEL (x_PCF) WAVEFORM

DATA RANGE WITH x_GAIN = 2

xP INPUT PIN

xM INPUT PIN

NOTES

1. x_PCF IS THE INSTANTANEOUS WAVEFORM OBTAINED

AFTER GAIN AND PHASE COMPENSATION.

Figure 31. Maximum Input Signal with Pseudo Differential Input with

Common-Mode Voltage = 0.1 V, Gain = 2

Each ADC contains a programmable gain amplifier that allows

a gain of 1, 2, or 4. The ADC produces full-scale output codes with

an input of ±1 V. With a gain of 1, this full-scale input corresponds

to a differential antiphase input of 0.707 V rms, as shown in

Figure 30. At a gain of 2, full-scale output codes are produced

with an input of 0.353 V rms, as shown in Figure 31. At a gain

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