ade7854 Analog Devices, Inc., ade7854 Datasheet - Page 21

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

Preliminary Technical Data
describes mathematically the function of the current waveform
gain registers.
Changing the content of AIGAIN[23:0], BIGAIN[23:0] or
CIGAIN[23:0] affects all calculations based on its current; that
is, it affects the corresponding phase active/reactive/apparent
energy and current rms calculation. In addition, waveform
samples are also scaled accordingly.
Note that the serial ports of the ADE7854 work on 32, 16 or 8-
bit words and the DSP works on 28 bits. The 24-bit AIGAIN,
BIGAIN and CIGAIN registers are accessed as 32-bit registers
with 4 most significant bits padded with 0s and sign extended
to 28 bits. See Figure 16 for details.
Current Channel HPF
The ADC outputs can contain a dc offset. This offset may
create errors in power and rms calculations. High Pass Filters
(HPF) are placed in the signal path of the phase currents and of
the phase voltages. If enabled, the HPF eliminates any dc offset
on the current channel. All filters are implemented in the DSP
and by default they are all enabled: 24-bit register
HPFDIS[23:0] is cleared to 0x00000000. All filters are disabled
by setting HPHDIS[23:0] to any non zero value.
Current
=
31
A
DC
0000
Figure 16. 24-bit xIGAIN (x=A,B,C) are transmitted as 32-bit words
Output
waveform
28
bits 27-24 equal
x
27
to bit 23
⎛
⎜ ⎜
⎝
1
=
+
Content
24
of
23
Current
2
24 bit number
bit 23 is sign bit
23
Gain
Register
⎞
⎟ ⎟
⎠
(1)
Rev. PrC| Page 21 of 71
0
As previously stated, the serial ports of the ADE7854 work on
32, 16 or 8-bit words. The HPFDIS register is accessed as a 32-
bit register with 8 most significant bits padded with 0s. See
Figure 17 for details.
Current Channel Sampling
The waveform samples of the current channel are taken at the
output of HPF and stored into IAWV, IBWV, ICWV 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 IAWV,
IBWV and ICWV registers are available to be read using I
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. When IAWV, IBWV, ICWV 24-bit signed
registers are read from the ADE7854, they are transmitted
signed extended to 32 bits. See Figure 18 for details.
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.
bits 31-24 equal to
31
Figure 18. 24-bit IxWV (x=A, B, C) are transmitted as 32-bit signed words
31
0000 0000
Figure 17. 24-bit HPFDIS register is transmitted as 32-bit word
bit 23
24
24
23
24 bit signed number
22
23
bit 23 is sign bit
24 bit number
0
ADE7854
2
C or
0