Datasheet

ADE7854/ADE7858/ADE7868/ADE7878 Data Sheet
Rev. G | Page 30 of 100
AIGAIN[23:0]
DS
P
REFERENCE
HPFDIS
[23:0]
DIGIT
A
L
INTEGRA
TOR
INTEN BIT
CONFIG[0]
TOTAL/FUNDAMENTAL
ACTIVE AND REACTIVE
POWER CALCULA
TION
CURRENT PEAK,
OVERCURRENT
DETECT
IAWV WAVEFORM
SAMPLE REGISTER
CURRENT RMS (IRMS)
CALCUL
ATION
HPF
ADC
PGA1
IAP
ZX DETECTION
PGA1 BITS
GAIN[2:0]
×1, ×2, ×4, ×8, ×16
V
IN
V
IN
IAN
ANALOG INPUT RANGE ADC OUTPUT RANGE
0x5A7540 =
+5,928,256
ZX SIGNA
L
DAT
A RANGE
0V
0xA58AC0 =
–5,928,256
0x5A7540 =
+5,928,256
CURRENT CHANNE
L
DATA RANGE AFTER
INTEGRATION
0V
0xA58AC0 =
–5,928,256
0x5A7540 =
+5,928,256
CURRENT CHANNEL
D
AT
A RANGE
0V
0xA58AC0 =
–5,928,256
+0.5V/GAIN
–0.5V/GAIN
0V
LPF1
08510-019
Figure 33. Current Channel Signal Path
NIGAIN[23:0]
DSP
REFERENCE
DIGITAL
INTEGRATOR
INTEN BIT
CONFIG[0]
INWV WA
VEFORM
SAMPLE REGISTER
CURRENT RMS (IRMS)
CALCULATION
HPF
ADC
PGA2
INP
PGA2 BITS
GAIN[5:3]
×1, ×2, ×4, ×8, ×16
V
IN
INN
08510-120
HPFDIS
[23:0]
Figure 34. Neutral Current Signal Path (ADE7868, ADE7878 Only)
Current Waveform Gain Registers
There is a multiplier in the signal path of each phase and
neutral current. The current waveform can be changed by
±100% by writing a corresponding twos complement number
to the 24-bit signed current waveform gain registers (AIGAIN,
BIGAIN, CIGAIN, and NIGAIN). 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 3 describes mathematically the function of the current
waveform gain registers.
Current Waveform =








+×
23
2
1
RegisterGainCurrentofContent
OutputADC
(3)
Changing the content of the AIGAIN, BIGAIN, CIGAIN, or
INGAIN registers 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 scale accordingly.
Note that the serial ports of the ADE7854, ADE7858, ADE7868,
and/or ADE7878 work on 32-, 16-, or 8-bit words, and the DSP
works on 28 bits. The 24-bit AIGAIN, BIGAIN, CIGAIN, and
NIGAIN registers are accessed as 32-bit registers with the four
most significant bits (MSBs) padded with 0s and sign extended
to 28 bits. See Figure 35 for details.
31
28 27 24
23 0
24-BIT NUMBER0000
BITS[27:24] ARE
EQUAL TO BIT 23
BIT 23 IS A SIGN BIT
08510-016
Figure 35. 24-Bit xIGAIN Transmitted as 32-Bit Words
Current Channel HPF
The ADC outputs can contain a dc offset. This offset can create
errors in power and rms calculations. High-pass filters (HPFs)
are placed in the signal path of the phase and neutral 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: the 24-bit HPFDIS
register is cleared to 0x00000000. All filters are disabled by
setting HPFDIS to any nonzero value.
As stated in the Current Waveform Gain Registers section, the
serial ports of the ADE78xx work on 32-, 16-, or 8-bit words.
The HPFDIS register is accessed as a 32-bit register with eight
MSBs padded with 0s. See Figure 36 for details.
31 24 23 0
24-BIT NUMBER0000 0000
08510-017
Figure 36. 24-Bit HPFDIS Register Transmitted as 32-Bit Word