ADE7758ARWZ Analog Devices Inc, ADE7758ARWZ Datasheet - Page 31

• Manufacturer Part Number: ADE7758ARWZ
• Description: IC ENERGY METERING 3PHASE 24SOIC
• Manufacturer: Analog Devices Inc

Specifications of ADE7758ARWZ

• Input Impedance: 380 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.8V
• Current - Supply: 8mA
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (0.300", 7.50mm Width)
• Meter Type: 3 Phase
• Ic Function: Poly Phase Multifunction Energy Metering IC
• Supply Voltage Range: 4.75V To 5.25V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: SOIC
• No. Of Pins: 24
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Active Power Gain Calibration
Note that the average active power result from the LPF output
in each phase can be scaled by ±50% by writing to the phase’s
watt gain register (AWG, BWG, or CWG). The watt gain
registers are twos complement, signed registers and have a
resolution of 0.024%/LSB. Equation 16 describes
mathematically the function of the watt gain registers.
The output is scaled by −50% by writing 0x800 to the watt gain
registers and increased by +50% by writing 0x7FF to them.
These registers can be used to calibrate the active power (or
energy) calculation in the ADE7758 for each phase.
Active Power Offset Calibration
The ADE7758 also incorporates a watt offset register on each
phase (AWATTOS, BWATTOS, and CWATTOS). These are
signed twos complement, 12-bit registers that are used to
remove offsets in the active power calculations. An offset can
exist in the power calculation due to crosstalk between channels
on the PCB or in the chip itself. The offset calibration allows the
contents of the active power register to be maintained at 0 when
no power is being consumed. One LSB in the active power
offset register is equivalent to 1/16 LSB in the active power
multiplier output. At full-scale input, if the output from the
multiplier is 0xCCCCD (838,861d), then 1 LSB in the LPF2
output is equivalent to 0.0075% of measurement error at 60 dB
down from full scale on the current channel. At −60 dB down
on full scale (the input signal level is 1/1000 of full-scale signal
inputs), the average word value from LPF2 is 838.861
(838,861/1000). One LSB is equivalent to 1/838.861/16 × 100%
= 0.0075% of the measured value. The active power offset register
has a correction resolution equal to 0.0075% at −60 dB.
Sign of Active Power Calculation
Note that the average active power is a signed calculation. If the
phase difference between the current and voltage waveform is
more than 90°, the average power becomes negative. Negative
power indicates that energy is being placed back on the grid.
The ADE7758 has a sign detection circuitry for active power
calculation.
LPF
Average
2
Output
Power
×
Data
⎛
⎜
⎝
1
+
=
Watt
Gain
2
12
Re
gister
⎞
⎟
⎠
(16)
Rev. D | Page 31 of 72
The REVPAP bit (Bit 17) in the interrupt status register is set if
the average power from any one of the phases changes sign. The
phases monitored are selected by TERMSEL bits in the
COMPMODE register (see Table 21). The TERMSEL bits are
also used to select which phases are included in the APCF and
VARCF pulse outputs. If the REVPAP bit is set in the mask
register, the IRQ logic output goes active low (see the
section). Note that this bit is set whenever there are sign
changes, that is, the REVPAP bit is set for both a positive-to-
negative change and a negative-to-positive change of the sign
bit. The response time of this bit is approximately 176 ms for a
full-scale signal, which has an average value of 0xCCCCD at the
low pass filter output. For smaller inputs, the time is longer.
The APCFNUM [15:13] indicate reverse power on each of the
individual phases. Bit 15 is set if the sign of the power on Phase A is
negative, Bit 14 for Phase B, and Bit 13 for Phase C.
No-Load Threshold
The ADE7758 has an internal no-load threshold on each phase.
The no-load threshold can be activated by setting the NOLOAD
bit (Bit 7) of the COMPMODE register. If the active power falls
below 0.005% of full-scale input, the energy is not accumulated
in that phase. As stated, the average multiplier output with full-
scale input is 0xCCCCD. Therefore, if the average multiplier
output falls below 0x2A, the power is not accumulated to avoid
creep in the meter. The no-load threshold is implemented only
on the active energy accumulation. The reactive and apparent
energies do not have the no-load threshold option.
Active Energy Calculation
As previously stated, power is defined as the rate of energy flow.
This relationship can be expressed mathematically as
Conversely, Energy is given as the integral of power.
Re
Power =
Energy
sponse
=
dEnergy
∫
Time
p
dt
( )
t
dt
≅
1
60
ms
+
⎡
⎢
⎢
⎣
Average
2
25
Value
⎤
⎥
⎥
⎦
ADE7758
×
CLKIN
Interrupts
4
(18)
(19)
(17)