ADE7933 datasheet(87/125 Pages) AD

87 / 125 page

Data Sheet

ADE7978/ADE7933/ADE7932/ADE7923

Rev. D | Page 87 of 125

APPLICATIONS INFORMATION

The ADE7978, ADE7933/ADE7932 and ADE7923 chipset was

designed for use in 3-phase energy metering systems in which

one master device, usually a microcontroller, manages the

ADE7978 through an I2C or SPI interface. The ADE7978 then

manages two, three, or four ADE7933/ADE7932 and ADE7923

devices. The ADE7978, ADE7933/ADE7932 and ADE7923

chipset can be used in in 3-phase 4-wire and 3-phase 3-wire

networks in a direct connection architecture. They cannot be

used in 3-phase networks that require an indirect connection

through current or voltage transformers as these require

physical separation of the current and voltage sensing circuits.

The ADE7978 is not the only chip capable of managing

multiple ADE7933/ADE7932 devices. Any microcontroller

that conforms to the ADE7933/ADE7932 and ADE7923 serial

interface can manage the devices correctly. (For more information,

see the Bit Stream Communication Between the ADE7978 and

the ADE7933/ADE7932 and ADE7923 section). However,

similar devices, such as the ADE7913/ADE7912 3-channel,

isolated, Σ-Δ ADCs with an SPI interface and ADE7903 3-

channel Σ-Δ ADCs with an SPI interface, may be more suitable

for direct interfacing with a microcontroller. For more

information about the ADE7913/ADE7912 and ADE7903

ADCs, see the product pages for these devices.

Figure 109 shows Phase A of a 3-phase energy meter. The Phase A

current, IA, is sensed with a shunt. A pole of the shunt is connected

to the IM pin of the ADE7933/ADE7932 and becomes the ground

of the isolated side of the ADE7933/ADE7932, GNDISO. The

Phase A to neutral voltage, VAN, is sensed with a resistor divider,

and the VM pin is also connected to the IM and GNDISO pins.

Note that the voltages measured by the ADCs of the ADE7933/

ADE7932 are opposite to VAN and IA, a classic approach in single-

phase metering. The other ADE7933/ADE7932 devices, which

monitor Phase B and Phase C, are connected in a similar way.

NEUTRAL

PHASE A

ADE7932/

ADE7933

GNDISO

V1P

VAN

Figure 109. Phase A ADE7933/ADE7932 Current and Voltage Sensing

Figure 110 shows how to connect the ADE7923 inputs when the

neutral line of a 3-phase system is monitored. The neutral

current is sensed using a shunt, and the voltage across the shunt

is measured at the fully differential inputs IP and IM.

The neutral to earth voltage or any voltage referenced to ground

can be sensed with a voltage divider at the single-ended inputs,

V1P and VM.

NEUTRAL

NEUTRAL LINE

ADE7923

V1P

GNDISO

Figure 110. Neutral Line and Auxiliary Voltage Monitoring

with the ADE7923

DIFFERENCES BETWEEN THE ADE7923 AND THE

ADE7933/ADE7932

The ADE7923 is a nonisolated Σ-Δ ADC similar to the

ADE7933. The performance of both the ADE7923 and

ADE7933/ADE7932 is identical, with the only differences

caused by the absence of an isolation barrier. The dynamic

range and accuracy of the ADE7923 is equal to that of the

ADE7933/ADE7932. The ADE7923 has two voltage channel

inputs, V1P and V2P, and one current channel input, IP. This

nonisolated ADC is useful when neutral current monitoring

is needed but there is no requirement for isolation from the

neutral line. It is important to note that the system is grounded

on the neutral line with this configuration.

The current channel is used for measuring neutral current

whereas the two voltage channels can be used for auxiliary

voltage measurements such as measuring a battery or any other

voltage measurement that is referenced to ground.

The ADE7923 is pin-to-pin-compatible with the ADE7933/

ADE7932 isolated ADCs and has the same footprint; therefore,

the ADE7923 and ADE7933/ADE7932 are direct swap-compatible.

ADE7978, ADE7933/ADE7932 AND ADE7923 IN

POLYPHASE ENERGY METERS

A polyphase energy meter must manage three phases and an

optional neutral line. Figure 111 shows an example of a 3-phase

meter built for a 4-wire wye configuration. Three ADE7933/

ADE7932 devices read the phase currents and voltages. An

ADE7923 manages the neutral line measurements. However, if

isolation is required, an ADE7933/ADE7932 can be used for the

neutral line to isolate it similarly to the other phases. If the

neutral line measurements are not required, only three

ADE7933/ADE7932 devices are used (see Figure 112); in this

configuration, the DATA_N pin of the ADE7978 is connected

to VDD.

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