EVAL-ADE7858EBZ datasheet(44/76 Pages) AD

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ADE7858

Preliminary Technical Data

Rev. PrA| Page 44 of 76

Description

power

IBWV

Phase B current

BWATT

Phase B active

power

VBWV

Phase B voltage

CWATT

Phase C active

power

ICWV

Phase C current

AVAR

Phase A reactive

power

VCWV

Phase C voltage

BVAR

Phase B reactive

power

AVA

Phase A apparent

power

CVAR

Phase C reactive

power

BVA

Phase B apparent

power

The bit 17 (DREADY) in STATUS0[31:0] register can be used

to signal when the registers mentioned in Table 17 may be read

using I2C or SPI serial ports. An interrupt attached to the flag

may be enabled by setting bit 17 (DREADY) in MASK0[31:0]

bit DREADY.

The ADE7858 contains a High Speed Data Capture (HSDC)

port that is specially designed to provide fast access to the

waveform sample registers. Read HSDC Interface section for

more details.

As previously stated, the serial ports of the ADE7858 work on

32, 16 or 8-bit words. All registers listed in Table 17 are

transmitted signed extended from 24 to 32 bits (see Figure 18).

ENERGY TO FREQUENCY CONVERSION

The ADE7858 provides 3 frequency output pins: CF1, CF2 and

CF3.

CF3 pin is multiplexed with HSCLK pin of HSDC interface.

When HSDC is enabled, the CF3 functionality is disabled at the

pin. CF1 and CF2 pins are always available. After initial

calibration at manufacturing, the manufacturer or end

customer verifies the energy meter calibration. One convenient

way to verify the meter calibration is to provide an output

frequency proportional to the active, reactive or apparent

powers under steady load conditions. This output frequency

can provide a simple, single-wire, optically isolated interface to

external calibration equipment. Figure 49 illustrates the energy-

to-frequency conversion in the ADE7858.



Instantaneous

phase A active

power

Digital Signal Processor

TERMSELx bits in

COMPMODE

CFxSEL bits in

CFMODE

WATT

VAR

Freq Divider

CFxDEN

CFx pulse

output

Instantaneous

phase B active

power

Instantaneous

phase C active

power



ACCUMULATOR

WTHR[47:0]

REVPSUMx bit of

STATUS0[31:0]

Figure 49. ADE7858 Energy to Frequency Conversion

The DSP computes the instantaneous values of all phase

powers: total active, total reactive and apparent. The process in

which the energy is sign accumulated in various hr registers

(watt-hr, var-hr and VA-hr) has already been described in

Energy Calculation chapters. In the energy to frequency

conversion process, the instantaneous powers are used to

generate signals at frequency output pins CF1, CF2 and CF3.

One digital to frequency converter is used for every CF pin.

Every converter sums certain phase powers and generates a

signal proportional to the sum. Two sets of bits decide what

powers are converted.

First, bits 2, 1, 0 (TERMSEL1[2:0]), 5, 4, 3 (TERMSEL2[2:0])

and 8, 7, 6 (TERMSEL3[2:0]) of COMPMODE[15:0] register

decide which phases or which combination of phases are added.

TERMSEL1 bits refer to CF1 pin, TERMSEL2 bits refer to CF2

pin and TERMSEL3 bits refer to CF3 pin. TERMSELx[0] bits,

x=1, 2, 3 manage phase A. When set to 1, phase A power is

included in the sum of powers at CFx converter. When cleared

to 0, phase A power is not included. TERMSELx[1] bits manage

phase B, TERMSELx[2] bits manage phase C. Setting all

TERMSELx bits to 1 means all 3 phase powers are added at CFx

converter. Clearing all TERMSELx bits to 0 means no phase

power is added and no CF pulse is generated.

Second, bits 2, 1, 0 (CF1SEL[2:0]), 5, 4, 3 (CF2SEL[2:0]) and 8,

7, 6 (CF3SEL[2:0]) in CFMODE[15:0] register decide what type

power is used at the inputs of CF1, CF2 and respective CF3

converters. Table 18 shows the values that CFxSEL may have:

total active, total reactive or apparent powers.

By default, TERMSELx bits are all 1 and CF1SEL bits are 000,

CF2SEL bits are 001 and CF3SEL bits are 010. This means that

by default, the CF1 digital to frequency converter produces

signals proportional to the sum of all 3 phase total active

EVAL-ADE7858EBZ Datasheet(PDF) 44 Page - Analog Devices

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