ADE7756.PDF

Active Energy Metering IC

with Serial Interface

ADE7756*

FEATURES

High Accuracy, Supports IEC 687/1036

Less than 0.1% Error over a Dynamic Range of 1000 to 1

An On-Chip User Programmable Threshold for Line

Voltage SAG Detection and PSU Supervisory

The ADE7756 Supplies Sampled Waveform Data

(20 Bits) and Active Energy (40 Bits)

Digital Power, Phase and Input Offset Calibration

An On-Chip Temperature Sensor ( 3 C Typical after

Calibration)

An SPI-Compatible Serial Interface

A Pulse Output with Programmable Frequency

An Interrupt Request Pin (IRQ) and Status Register

Provide Early Warning of Register Overflow and

Other Conditions

Proprietary ADCs and DSP Provide High Accuracy

over Large Variations in Environmental Conditions

and Time

Reference 2.4 V 8% (20 ppm/ C Typical) with External

Overdrive Capability

Single 5 V Supply, Low Power (25 mW Typical)

The ADE7756 contains a sampled Waveform register and an

Active Energy register capable of holding at least five seconds of

accumulated power at full load. Data is read from the ADE7756

via the serial interface. The ADE7756 also provides a pulse output

(CF) with a frequency that is proportional to the active power.

In addition to real power information, the ADE7756 also provides

system calibration features, i.e., channel offset correction, phase

calibration, and power calibration. The part also incorporates a

detection circuit for short duration low voltage variations or sags.

The voltage threshold level and the duration (in number of half-

line cycles) of the variation are user programmable. An open drain

logic output ( SAG ) goes active low when a sag event occurs.

A zero crossing output (ZX) produces an output that is synchro-

nized to the zero crossing point of the line voltage. This output can

be used to extract timing or frequency information from the line.

The signal is also used internally to the chip in the calibration

mode. This permits faster and more accurate calibration of the

real power calculation. This signal is also useful for synchronization

of relay switching with a voltage zero crossing, thus improving

the relay life by reducing the risk of arcing.

The interrupt request output is an open drain, active low logic

output. The IRQ output will become active when the accumu-

lated real power register is half-full and also when the register

overflows. A status register indicates the nature of the interrupt.

The ADE7756 is available in 20-lead DIP and 20-lead

SSOP packages.

GENERAL DESCRIPTION

The ADE7756 is a high-accuracy electrical power measurement

IC with a serial interface and a pulse output. The ADE7756

incorporates two second-order sigma-delta ADCs, reference

circuitry, temperature sensor, and all the signal processing

required to perform active power and energy measurement.

FUNCTIONAL BLOCK DIAGRAM

AV DD

RESET

DV DD

DGND

PGA

MULTIPLIER

HPF1

MULTIPLIER

LPF2

ADE7756

V1P

V1N

ADC

SAG

TEMP

SENSOR

APGAIN[11:0]

APOS[11:0]

PHCAL[5:0]

V2P

V2N

ADC

DFC

2.4V

REFERENCE

ADE7756 REGISTERS

AND

SERIAL INTERFACE

LPF1

CFDIV[11:0]

AGND

REF IN/OUT

DIN DOUT SCLK CS

IRQ

CLKIN

CLKOUT

* U.S. Patents 5,745,323; 5,760,617; 5,862,069; 5,872,469; other pending.

REV. 0

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties that

may result from its use. No license is granted by implication or otherwise

under any patent or patent rights of Analog Devices.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

www.analog.com

Fax: 781/326-8703

ADE7756

TABLE OF CONTENTS

FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . 1

FUNCTIONAL BLOCK DIAGRAM . . . . . . . . . . . . . . . . . 1

ADE7756–SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . 3

TIMING CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . 5

ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . 6

ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

PIN CONFIGURATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

PIN FUNCTION DESCRIPTIONS . . . . . . . . . . . . . . . . . . 6

TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

MEASUREMENT ERROR . . . . . . . . . . . . . . . . . . . . . . . . . 8

PHASE ERROR BETWEEN CHANNELS . . . . . . . . . . . . . 8

POWER SUPPLY REJECTION . . . . . . . . . . . . . . . . . . . . . . 8

ADC OFFSET ERROR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

GAIN ERROR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

GAIN ERROR MATCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

ANALOG INPUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

ZERO CROSSING DETECTION . . . . . . . . . . . . . . . . . . . 13

LINE VOLTAGE SAG DETECTION . . . . . . . . . . . . . . . . 14

Sag Level Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

POWER SUPPLY MONITOR . . . . . . . . . . . . . . . . . . . . . . 14

INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Using the ADE7756 Interrupts with an MCU . . . . . . . . . 15

Interrupt Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

TEMPERATURE MEASUREMENT . . . . . . . . . . . . . . . . 16

ANALOG-TO-DIGITAL CONVERSION . . . . . . . . . . . . . 16

Antialias Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

ADC Transfer Function . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Reference Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

CHANNEL 1 ADC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Channel 1 ADC Gain Adjust . . . . . . . . . . . . . . . . . . . . . . 18

Channel 1 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

CHANNEL 2 ADC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Channel 2 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

PHASE COMPENSATION . . . . . . . . . . . . . . . . . . . . . . . . 20

ACTIVE POWER CALCULATION . . . . . . . . . . . . . . . . . 21

ENERGY CALCULATION . . . . . . . . . . . . . . . . . . . . . . . . 22

Integration Times under Steady Load . . . . . . . . . . . . . . . 23

POWER OFFSET CALIBRATION . . . . . . . . . . . . . . . . . . 23

ENERGY-TO-FREQUENCY CONVERSION . . . . . . . . . 23

ENERGY CALIBRATION . . . . . . . . . . . . . . . . . . . . . . . . . 24

CALIBRATING THE ENERGY METER . . . . . . . . . . . . . 24

Calculating the Average Active Power . . . . . . . . . . . . . . . 24

Calibrating the Frequency at CF . . . . . . . . . . . . . . . . . . . 24

Energy Meter Display . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

CLKIN FREQUENCY . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

APPLICATION INFORMATION . . . . . . . . . . . . . . . . . . . 25

SUSPENDING THE ADE7756 FUNCTIONALITY . . . . 26

SERIAL INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Serial Write Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Serial Read Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Communications Register . . . . . . . . . . . . . . . . . . . . . . . . 29

Mode Register (06H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Interrupt Status Register (04H)/Reset Interrupt

Status Register (05H) . . . . . . . . . . . . . . . . . . . . . . . . . . 31

OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . 32

–2–

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ADE7756

SPECIFICATIONS 1

Parameter

(AV DD = DV DD = 5 V

5%, AGND = DGND = 0 V, On-Chip Reference, CLKIN = 3.579545 MHz XTAL,

T MIN to T MAX = –40

C to +85

C, unless otherwise noted.)

A Version B Version Unit

Test Conditions/Comments

ENERGY MEASUREMENT ACCURACY

Measurement Bandwidth

kHz

CLKIN = 3.579545 MHz

Measurement Error 1 on Channel 1

Channel 2 = 300 mV rms/60 Hz, Gain = 2

Channel 1 Range = 1 V Full Scale

Gain = 1

0.1

% typ