ADE7759ARS datasheet(26/32 Pages) AD

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ADE7759

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Table III. Frequency Dependencies of the ADE7759 Parameters

Parameter

CLKIN Dependency

Nyquist frequency for CH 1 and 2 ADCs

CLKIN/8

PHCAL resolution (seconds per LSB)

4/CLKIN

Active Energy register update rate (Hz)

CLKIN/4

Waveform sampling rate (Number of

samples per second)

WAVSEL 1, 0 = 0

CLKIN/128

CLKIN/256

CLKIN/512

CLKIN/1024

Maximum ZXTOUT period

524,288/CLKIN

SUSPENDING THE ADE7759 FUNCTIONALITY

The analog and the digital circuit can be suspended separately.

The analog portion of the ADE7759 can be suspended by setting

the ASUSPEND bit (Bit 4) of the mode register to logic high—

see Mode Register. In suspend mode, all waveform samples from

the ADCs will be set to zeros. The digital circuitry can be halted

by stopping the CLKIN input and maintaining a logic high or

low on CLKIN pin. The ADE7759 can be reactivated by restoring

the CLKIN input and setting the ASUSPEND bit to logic low.

APPLICATION INFORMATION

Application note AN-564 contains detailed information on how to

design a ANSI Class 100 Watt-Hour meter based on the ADE7756,

a pin-to-pin compatible product with the ADE7759. Application

Note AN-578 describes an algorithm on how to calculate the voltage

and current rms values using an external MCU. It is available from

the ADE7756 product homepage under the Application Note link

on the energy metering homepage, www.analog.com/energymeter.

SERIAL INTERFACE

All ADE7759 functionality is accessible via several on-chip

registers—see Figure 41. The contents of these registers can be

updated or read using the on-chip serial interface. After power-on

or toggling the

RESET pin low or a falling edge on CS, the

ADE7759 is placed in communications mode. In communications

mode the ADE7759 expects a write to its Communications register.

The data written to the Communications register determines

whether the next data transfer operation will be a read or a write

and also which register is accessed. Therefore, all data transfer

operations with the ADE7759, whether a read or a write, must

begin with a write to the Communications register.

COMMUNICATIONS

OUT

ADDRESS

DECODE

DIN

DOUT

Figure 41. Addressing ADE7759 Registers via the

Communications Register

The Communications register is an 8-bit wide register. The MSB

determines whether the next data transfer operation is a read or

a write. The five LSBs contain the address of the register to be

accessed. See Communications Register section for a more

detailed description. Figure 42 and Figure 43 show the data

transfer sequences for a read and write operation, respectively.

On completion of a data transfer (read or write) the ADE7759

once again enters communications mode.

DIN

SCLK

DOUT

COMMUNICATIONS REGISTER WRITE

MULTIBYTE READ DATA

ADDRESS

Figure 42. Reading Data from the ADE7759 via the

Serial Interface

DIN

SCLK

COMMUNICATIONS REGISTER WRITE

ADDRESS

MULTIBYTE WRITE DATA

Figure 43. Writing Data to the ADE7759 via the Serial

Interface

A data transfer is complete when the LSB of the ADE7759

or from the ADE7759.

The Serial Interface of the ADE7759 is made up of four signals:

SCLK, DIN, DOUT and

CS. The serial clock for a data transfer is

applied at the SCLK logic input. This logic input has a Schmitt-

trigger input structure, which allows slow rising (and falling)

clock edges to be used. All data transfer operations are synchro-

nized to the serial clock. Data is shifted into the ADE7759 at the

DIN logic input on the falling edge of SCLK. Data is shifted out

of the ADE7759 at the DOUT logic output on a rising edge of

SCLK. The

CS logic input is the chip select input. This input is

used when multiple devices share the serial bus. A falling edge on

CS also resets the serial interface and places the ADE7759 in

communications mode. The

CS input should be driven low for

the entire data transfer operation. Bringing

CS high during a data

transfer operation will abort the transfer and place the serial bus

in a high impedance state. The

CS logic input may be tied low if

the ADE7759 is the only device on the serial bus. However with

tied low, all initiated data transfer operations must be fully com-

pleted, i.e., the LSB of each register must be transferred as there is

no other way of bringing the ADE7759 back into communications

mode without resetting the entire device, i.e., using

RESET.

Serial Write Operation

The serial write sequence takes place as follows. With the ADE7759

in communications mode (i.e., the

CS input logic low), a write to

the Communications register first takes place. The MSB of this

byte transfer is a 1, indicating that the data transfer operation is

a write. The LSBs of this byte contain the address of the register

to be written to. The ADE7759 starts shifting in the register data

on the next falling edge of SCLK. All remaining bits of register

data are shifted in on the falling edge of subsequent SCLK

pulses—see Figure 44.

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