ADE7753
–20–REV. PrC 01/02
PRELIMINARY TECHNICAL DATA
HPF
LPF2
Current Signal - i(t)
Voltage Signal - v(t)
Instantaneous
Power Signal - p(t)
MULTIPLIER
Active Power
Signal - P
CCCCDh
I
V
19999Ah
000000h
WGAIN[11:0]
S
+
2
-6
2
-7
APOS[15:0]
sgn 2
-8
2
6
2
5
32
24
+For Energy
Accumulation
For Waveform
Sampling
19999h
24
Figure 33
– Active Power Signal Processing
Voltage
Current
Instantaneous
Power Signal
Active Real Power
Signal = V x I
V. I.
00000h
19999Ah
CCCCDh
v(t) = √2×V×sin(ωt)
i(t) = √2×I×sin(ωt)
p(t) = V×I-V×I×cos(2ωt)
Figure 31– Active Power Calculation
Since LPF2 does not have an ideal “brick wall” frequency
response—see Figure 32, the Active Power signal will have
some ripple due to the instantaneous power signal.
Frequency
1.0Hz 3.0Hz
10Hz 30Hz
100Hz
-24
-20
-16
-12
-8
-4
0
dBs
Figure 32 —Frequency Response of LPF2
This ripple is sinusoidal and has a frequency equal to twice
the line frequency. Since the ripple is sinusoidal in nature it
will be removed when the Active Power signal is integrated
to calculate Energy – see Energy Calculation.
Figure 33 shows the signal processing chain for the
ActivePower calculation in the ADE7753. As explained, the
Active Power is calculated by low pass filtering the instanta-
neous power signal. Note that for when reading the waveform
samples from the output of LPF2,
The gain of the Active Energy can be adjusted by using the
multiplier and Watt Gain register (WGAIN[11:0]). The
gain is adjusted by writing a 2’s complement 12-bit word to
the Watt Gain register. Below is the expression that shows
how the gain adjustment is related to the contents of the Watt
Gain register.
+×= 12
2
1WGAIN
PowerActiveWGAINOutput
For example when 7FFh is written to the Watt Gain register
the Power output is scaled up by 50%. 7FFh = 2047d,
2047/2
12
= 0.5. Similarly, 800h = -2048 Dec (signed 2’s
Complement) and power output is scaled by –50%.
Shown in Figure 34 is the maximum code (Hexadecimal)
output range for the Active Power signal (LPF2). Note that
the output range changes depending on the contents of the
Watt Gain register. The minimum output range is given
when the Watt Gain register contents are equal to 800h, and
the maximum range is given by writing 7FFh to the Watt
Gain register. This can be used to calibrate the Active Power
(or Energy) calculation in the ADE7753.
00000h
+ 40% FS
- 40% FS
+ 60% FS
+ 20% FS
- 20% FS
- 60% FS
CCCCDh
F33333h
WGAIN[11:0]
000h 7FFh 800h
Active Power
Calibration Range
Positive
Power
Negative
Power
Active Power Output
66666h
F9999Ah
133333h
ECCCCDh
Figure 34 – Active Power Calculation Output Range