Datasheet

ADE7753
Rev. C | Page 29 of 60
APOS[15:0]
WGAIN[11:0]
WDIV[7:0]
LPF2
CURRENT
CHANNEL
VOLTAGE
CHANNEL
OUTPUT LPF2
TIME (nT)
4
CLKIN
T
ACTIVE POWER
SIGNAL
+
+
AENERGY [23:0]
OUTPUTS FROM THE LPF2 ARE
ACCUMULATED (INTEGRATED) IN
THE INTERNAL ACTIVE ENERGY REGISTER
UPPER 24 BITS ARE
ACCESSIBLE THROUGH
AENERGY[23:0] REGISTER
23 0
48 0
WAVEFORM
REGISTER
VALUES
02875-0-063
%
Figure 63. ADE7753 Active Energy Calculation
Figure 63 shows the signal processing chain for the active power
calculation in the ADE7753. As explained, the active power is
calculated by low-pass filtering the instantaneous power signal.
Note that 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 twos complement 12-bit word to the
watt gain register. Equation 11 shows how the gain adjustment
is related to the contents of the watt gain register:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
⎭
⎬
⎫
⎩
⎨
⎧
+×=
12
2
1
WGAIN
PowerActiveWGAINOutput
(11)
For example, when 0x7FF is written to the watt gain register, the
power output is scaled up by 50%. 0x7FF = 2047d, 2047/2
12
=
0.5. Similarly, 0x800 = –2048d (signed twos complement) and
power output is scaled by –50%. Each LSB scales the power output
by 0.0244%. Figure 64 shows the maximum code (in hex) 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 0x800, and the maximum range is given by
writing 0x7FF to the watt gain register. This can be used to
calibrate the active power (or energy) calculation in the ADE7753.
0x133333
0xCCCCD
0x66666
0xF9999A
0xF33333
0xECCCCD
0x00000
ACTIVE POWER OUTPUT
POSITIVE
POWER
NEGATIVE
POWER
0x000 0x7FF 0x800
{WGAIN[11:0]}
ACTIVE POWER
CALIBRATION RANGE
02875-0-062
Figure 64. Active Power Calculation Output Range
ENERGY CALCULATION
As stated earlier, power is defined as the rate of energy flow.
This relationship can be expressed mathematically in Equation 12.
dt
dE
P =
(12)
where:
P is power.
E is energy.
Conversely, energy is given as the integral of power.
∫
= PdtE (13)