ADE9078ACPZ datasheet(30/108 Pages) AD

30 / 108 page

Data Sheet

ADE9078

Rev. 0 | Page 29 of 107

Current Channel Measurement Update Rates

Table 9 indicates the registers that hold current channel

measurements and the rate at which they update.

Table 9. Current Channel Measurement Update Rates

Description

Update

Rate

(kSPS)

AI_SINC_DAT

IA sinc4 filter output

BI_SINC_DAT

IB sinc4 filter output

CI_SINC_DAT

IC sinc4 filter output

NI_SINC_DAT

IN sinc4 filter output

AI_LPF__DAT

IA sinc4 + IIR low-pass filter

output and decimation

BI_LPF__DAT

IB sinc4 + IIR low-pass filter

output and decimation

CI_LPF__DAT

IC sinc4 + IIR low-pass filter

output and decimation

NI_LPF__DAT

IN sinc4 + IIR low-pass filter

output and decimation

AI_PCF

Instantaneous current on IA

BI_PCF

Instantaneous current on IB

CI_PCF

Instantaneous current on IC

NI_PCF

Instantaneous current on IN

AIRMS

Filtered based total rms of IA

BIRMS

Filtered based total rms of IB

CIRMS

Filtered based total rms of IC

NIRMS

Filtered based total rms of IN

ISUMRMS

Filtered rms of sum of

instantaneous currents

(AI_PCF + BI_PCF +

CI_PCF ± NI_PCF) (see the

Neutral Current RMS, RMS of

Sum of Instantaneous

Currents section)

IPEAK

Peak current channel

sample (see the Peak

Detection section)

ANGLx_x

Voltage to current or

current to current phase

angle (see the Angle

Measurement section)

CLKIN/24 =

512

ADC_REDIRECT Multiplexer

The ADE9078 provides a multiplexer that allows any ADC

output to be redirected to any digital processing datapath.

By default, each modulator is mapped to its corresponding

datapath. For example, the IAP and IAN pins go into the IA

modulator, which is mapped to the IxA digital processing

datapath. Write to the ADC_REDIRECT register to change the

ADC to digital channel mapping.

The redirection can be useful to simplify PCB layout,

depending on if the ADE9078 is on the top or bottom of the

PCB by redirecting the IA ADC output to the IC digital datapath

and the IC ADC output to the IA digital datapath. To achieve

this configuration, write IA_DIN = 010 and IC_DIN = 000 in

the ADC_REDIRECT register.

Alternatively, the VA voltage channel output can be used for all

three datapaths by writing VB_DIN = 100 and VC_DIN = 100

in the ADC_REDIRECT register.

The neutral current channel does not offer a zero-crossing

output or angle measurements. To calibrate the phase of the

neutral current NI_PCF signal, direct the neutral current ADC

output to Phase B digital current channel and check how its

angle corresponds to Phase A by writing IA_DIN = 111.

REFERENCE

Σ-Δ

MODULATOR

VIN

IA_DIN[2:0]

AI_SINC_DAT

AI_LPF_DAT

IA_MOD

011

IB_MOD

IC_MOD

IN_MOD

VA_MOD

VB_MOD

VC_MOD

IA_MOD

000

001

010

100

101

110

111

Figure 43. ADC_REDIRECT Modulator to Digital Datapath Multiplexing

Current Channel Gain, xIGAIN

There are many sources of gain error in an energy metering

system. The current sensor, including current transformer burden

resistors, may have some error. There is device to device gain

error in the ADE9078 device itself and the voltage reference

may have some variation (see Table 1 for the device

specifications).

The ADE9078 provides a current gain calibration register so

that each metering device has the same current channel scaling.

The current channel gain varies with xIGAIN as shown in the

following equation:

GAIN

HPF

xIGAIN

Gain

Channel

Current











 +

Use the following equation to calculate the xIGAIN value for a

given current channel gain:

xIGAIN = round((Current Channel Gain − 1) × 227)

where round() is a function to round to the nearest integer.

The current channel gain can be positive or negative.

For example, to increase the gain of the current channel up by

10% to 1.1,

xIGAIN = round((1.1 − 1) × 227) = 13,421,773 =

0x00CC CCCD

To decrease the gain by 10% to 0.9:

xIGAIN = round((0.9 − 1) × 227) = −13,421,773 =

0xFF33 3333

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