ade7854 Analog Devices, Inc., ade7854 Datasheet - Page 23

• Manufacturer Part Number: ade7854
• Description: Poly Phase Multifunction Energy Metering Ic With Neutral Current Measurement
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
32-bit register with 4 most significant bits padded with 0s and
sign extended to 28 bits.
When the digital integrator is switched off, the ADE7854 can be
used directly with a conventional current sensor, such as a
current transformer (CT).
VOLTAGE CHANNEL ADC
Figure 25 shows the ADC and signal processing chain for the
input VA in the voltage channel. The VB and VC channels have
similar processing chains. The ADC outputs are signed twos
complement 24-bit words and are available at a rate of 8 kSPS.
With the specified full-scale analog input signal of ±0.5 V, the
ADC produces its maximum output code value. This diagram
shows a full-scale voltage signal being applied to the differential
inputs VA and VN. The ADC output swings between
−5,928,256 (0xA558AC0) and +5,928,256 (0x5A7540).
Voltage Waveform Gain Registers
There is a multiplier in the signal path of each phase voltage.
The voltage waveform can be changed by ±100% by writing a
correspondent twos complement number to the 24-bit signed
current waveform gain registers (AVGAIN[23:0],
BVGAIN[23:0] and CVGAIN[23:0]). For example, if 0x400000
is written to those registers, the ADC output is scaled up by
50%. To scale the input by -50%, write 0xC00000 to the
registers. Equation (7) describes mathematically the function of
the current waveform gain registers.
Changing the content of AVGAIN[23:0], BVGAIN[23:0] and
CVGAIN[23:0] affects all calculations based on its voltage; that
is, it affects the corresponding phase active/reactive/apparent
Voltage
=
A
DC
Output
waveform
x
⎛
⎜ ⎜
⎝
1
=
+
Content
of
Voltage
2
23
Gain
Register
⎞
⎟ ⎟
⎠
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energy and voltage rms calculation. In addition, waveform
samples are also scaled accordingly.
As previously stated, the serial ports of the ADE7854 work on
32, 16 or 8-bit words and the DSP works on 28 bits. As
presented in Figure 16, AVGAIN, BVGAIN and CVGAIN
registers are accessed as 32-bit registers with 4 most significant
bits padded with 0s and sign extended to 28 bits.
Voltage Channel HPF
As seen in Current Channel HPF section, the ADC outputs can
contain a dc offset that can create errors in power and rms
calculations. High Pass Filters (HPF) are placed in the signal
path of the phase voltages, similar to the ones in the current
channels. HPFDIS[23:0] register may enable or disable the
filters. See Current Channel HPF section for more details.
Voltage Channel Sampling
The waveform samples of the current channel are taken at the
output of HPF and stored into VAWV, VBWV and VCWV 24-
bit signed registers at a rate of 8kSPS. All power and rms
calculations remain uninterrupted during this process. Bit 17
(DREADY) in STATUS0[31:0] register is set when VAWV,
VBWV and VCWV registers are available to be read using I
or SPI serial ports. Setting bit 17 (DREADY) in MASK0[31:0]
register enables an interrupt to be set when the DREADY flag is
set. See Digital Signal Processor chapter for more details on bit
DREADY.
As previously stated, the serial ports of the ADE7854 work on
32, 16 or 8-bit words. Similar to registers presented in Figure 18,
VAWV, VBWV and VCWV 24-bit signed registers are
transmitted signed extended to 32 bits.
The ADE7854 contains a High Speed Data Capture (HSDC)
port that is specially designed to provide fast access to the
waveform sample registers. See HSDC Interface section for
more details.
ADE7854
2
C