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ADE7978/ADE7933/ADE7932

Data Sheet

Rev. 0 | Page 82 of 120

APPLICATIONS INFORMATION

The ADE7978 and ADE7933/ADE7932 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 devices.

The ADE7978 is not the only chip capable of managing

multiple ADE7933/ADE7932 devices. Any microcontroller

that conforms to the ADE7933/ADE7932 serial interface can

manage the devices correctly. (For more information, see the Bit

Stream Communication Between the ADE7978 and the

ADE7933/ADE7932 section). However, similar devices, such as

the ADE7913/ADE7912 3-channel, isolated, Σ-Δ ADCs with an

SPI interface, may be more suitable for direct interfacing with a

microcontroller. For more information about the ADE7913/

ADE7912 ADCs, see the product pages for these devices.

Figure 101 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

PHASE A

ADE7932/

ADE7933

GNDISO

V1P

VAN

Figure 101. Phase A ADE7933/ADE7932 Current and Voltage Sensing

Figure 102 shows how to connect the ADE7933/ADE7932

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 is sensed with a voltage

divider at the single-ended inputs V1P and VM.

NEUTRAL

EARTH

NEUTRAL LINE

ADE7932/

ADE7933

V1P

GNDISO

Figure 102. Neutral Line and Neutral to Earth Voltage Monitoring

with the ADE7933/ADE7932

ADE7978 AND ADE7933/ADE7932 IN POLYPHASE

ENERGY METERS

A polyphase energy meter must manage three phases and an

optional neutral line. Figure 103 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. The

fourth ADE7933/ADE7932 manages the neutral line measure-

ments. If the neutral line measurements are not required, only

three ADE7933/ADE7932 devices are used (see Figure 104); in

this configuration, the DATA_N pin of the ADE7978 is

connected to VDD.

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