ADE7878ACPZ Analog Devices Inc, ADE7878ACPZ Datasheet - Page 29

• Manufacturer Part Number: ADE7878ACPZ
• Description: IC ENERGY METERING 3PH 40LFCSP
• Manufacturer: Analog Devices Inc

Specifications of ADE7878ACPZ

• Input Impedance: 400 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.4V
• Current - Supply: 22mA
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 40-WFQFN, CSP Exposed Pad
• Meter Type: 3 Phase
• Supply Voltage Range: 3V To 3.6V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: LFCSP
• No. Of Pins: 40
• Msl: MSL 1 - Unlimited
• Peak Reflow Compatible (260 C): Yes
• Supply Voltage Min: 3V
• Rohs Compliant: Yes
• Leaded Process Compatible: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Current Channel Sampling
The waveform samples of the current channel are taken at the
output of HPF and stored in the 24-bit signed registers, IAWV,
IBWV, ICWV, and INWV (ADE7868 and ADE7878 only) at a
rate of 8 kSPS. All power and rms calculations remain uninter-
rupted during this process. Bit 17 (DREADY) in the STATUS0
register is set when the IAWV, IBWV, ICWV, and INWV registers
are available to be read using the I
Bit 17 (DREADY) in the MASK0 register enables an interrupt
to be set when the DREADY flag is set. See the Digital Signal
Processor section for more details on Bit DREADY.
As stated in the Current Waveform Gain Registers section, the
serial ports of the ADE78xx work on 32-, 16-, or 8-bit words.
When the IAWV, IBWV, ICWV, and INWV 24-bit signed
registers are read from the ADE78xx (INWV is available on
ADE7868/ADE7878 only), they are transmitted sign extended
to 32 bits. See Figure 35 for details.
The ADE7854/ADE7858/ADE7868/ADE7878 devices each
contain a high speed data capture (HSDC) port that is specially
designed to provide fast access to the waveform sample registers.
See the HSDC Interface section for more details.
di/dt CURRENT SENSOR AND DIGITAL INTEGRATOR
The di/dt sensor detects changes in the magnetic field caused by
the ac current. Figure 36 shows the principle of a di/dt current
sensor.
The flux density of a magnetic field induced by a current is
directly proportional to the magnitude of the current. The
changes in the magnetic flux density passing through a conductor
Figure 35. 24-Bit IxWV Register Transmitted as 32-Bit Signed Word
31
EQUAL TO BIT 23
BITS[31:24] ARE
Figure 36. Principle of a di/dt Current Sensor
24 23 22
MAGNETIC FIELD CREATED BY CURRENT
(DIRECTLY PROPORTIONAL TO CURRENT)
BIT 23 IS A SIGN BIT
24-BIT SIGNED NUMBER
+ EMF (ELECTROMOTIVE FORCE)
– INDUCED BY CHANGES IN
2
C or SPI serial port. Setting
MAGNETIC FLUX DENSITY (di/dt)
0
Rev. D | Page 29 of 96
loop generate an electromotive force (EMF) between the two
ends of the loop. The EMF is a voltage signal that is propor-
tional to the di/dt of the current. The voltage output from the
di/dt current sensor is determined by the mutual inductance
between the current carrying conductor and the di/dt sensor.
Due to the di/dt sensor, the current signal needs to be filtered
before it can be used for power measurement. On each phase and
neutral current datapath, there is a built-in digital integrator to
recover the current signal from the di/dt sensor. The digital inte-
grator is disabled by default when the ADE78xx is powered up
and after a reset. Setting Bit 0 (INTEN) of the CONFIG register
turns on the integrator. Figure 37 and Figure 38 show the
magnitude and phase response of the digital integrator.
Note that the integrator has a −20 dB/dec attenuation and
approximately −90° phase shift. When combined with a di/dt
sensor, the resulting magnitude and phase response should be a
flat gain over the frequency band of interest. However, the di/dt
sensor has a 20 dB/dec gain associated with it and generates sig-
nificant high frequency noise. An antialiasing filter of at least
the second order is needed to avoid noise aliasing back in the
band of interest when the ADC is sampling (see the Antialiasing
Filter section).
The DICOEFF 24-bit signed register is used in the digital
integrator algorithm. At power-up or after a reset, its value is
0x000000. Before turning on the integrator, this register must be
initialized with 0xFFF8000. DICOEFF is not used when the
integrator is turned off and can remain at 0x000000 in that case.
ADE7854/ADE7858/ADE7868/ADE7878
–100
–50
–50
50
0
0
0.01
0
Figure 37. Combined Gain and Phase Response of the
500
0.1
1000
Digital Integrator
1500
1
FREQUENCY (Hz)
FREQUENCY (Hz)
2000
10
2500
100
3000
3500
1000
4000