ADE7754 Analog Devices, ADE7754 Datasheet - Page 20

• Manufacturer Part Number: ADE7754
• Description: Poly-phase Multi-Function Energy Metering IC with Serial Port
• Manufacturer: Analog Devices

ADE7754
Since LPF2 does not have an ideal “brick wall” frequency
response—see Figure 21, the Active Power signal will have
some ripple due to the instantaneous power signal. This
ripple is sinusoidal and has a frequency equal to twice the line
frequency. Since the ripple is sinusoidal in nature, it is
removed when the Active Power signal is integrated to
calculate the Energy – see Energy Calculation.
Figure 22 shows the signal processing in each phase for the
Active Power in the ADE7754.
Figure 23 shows the maximum code (Hexadecimal) output
range of the Active Power signal (after AWG). Note that the
output range changes depending on the contents of the Active
Power Gain and Watt Gain registers – see Current channel
ADC. The minimum output range is given when the Active
Power Gain and Watt Gain registers contents are equal to
800h and the maximum range is given by writing 7FFh to the
Active Power Gain and Watt Gain registers. These can be
used to calibrate the Active Power (or Energy) calculation in
the ADE7754 for each phase and also the Total Active
Energy -see Total Active Power calculation.
Figure 21 – Frequency response of the LPF used to filter
-12
-16
-20
-24
-4
-8
0
1.0Hz
Instantaneous Power in each phase
V
28F5C2h
D70A3Eh
3.0Hz
I
00h
Current Signal - i(t)
D70Bh
-100% to +100% FS
28F5h
00h
Voltage Signal - v(t)
-100% to + 100% FS
PRELIMINARY TECHNICAL DATA
Frequency
HPF
10Hz
8Hz
1
1V / GAIN1
1V / GAIN2
Figure 22 – Active Power Signal Processing
30Hz
Instantaneous Power Signal - p(t)
MULTIPLIER
24
sgn
sgn sgn sgn sgn 2 10
LPF2
–20–
28
Power Offset Calibration
The ADE7754 also incorporates an Active Offset register on
each phase (AAPOS, BAPOS and CAPOS). These are
signed 2’s complement 12-bit registers which can be used to
remove offsets in the active power calculations. An offset may
exist in the power calculation due to cross talk between
channels on the PCB or in the IC itself. The offset calibration
allows the contents of the Active Power register to be
maintained at zero when no power is being consumed.
1 LSBs in the Active Power Offset register is equivalent to 1
LSB in the 28-bit Energy bus displayed on Figure 22. Each
time power is added to the internal Active Energy register, the
content of the Active Power Offset register is added -see Total
Active Power calculation. Assuming the average value from
LPF2 is 8637BCh (8,796,092d) with full AC scale inputs on
current channel and voltage channel, then 1 LSB in the LPF2
output is equivalent to 0.011% of measurement error at -
60dB down of full scale - see Calibration of a 3-phase meter
based on the ADE7754.
APOS[11:0]
EC56D5Ch
S
13A92A4h
68DB8Ch
0000000h
D1B717h
2E48E9h
972474h
+
Active Power
2
4
2
3
2
2
000h 7FFh
2
1
AWG
2
0
12
Voltage channel ± 0.5V / GAIN2
Current channel ± 0.5V / GAIN1
D1B717h
800h
Active Power
Signal - P
- 50% FS
- 100% FS
- 150% FS
+ 150% FS
+ 100% F5
+ 50% FS
AAPGAIN[11:0] or
AWGAIN[11:0]
REV. PrG 01/03