ADE7758ARW Analog Devices Inc, ADE7758ARW Datasheet - Page 33

• Manufacturer Part Number: ADE7758ARW
• Description: IC ENERGY METERING 24-SOIC
• Manufacturer: Analog Devices Inc

Specifications of ADE7758ARW

• Rohs Status: RoHS non-compliant
• 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
• Lead Free Status / RoHS Status: Not Compliant

Integration Time Under Steady Load
The discrete time sample period (T) for the accumulation register
is 0.4 μs (4/CLKIN). With full-scale sinusoidal signals on the
analog inputs and the watt gain registers set to 0x000, the average
word value from each LPF2 is 0xCCCCD (see Figure 64 and
Figure 66). The maximum value that can be stored in the watt-
hr accumulation register before it overflows is 2
Because the average word value is added to the internal register,
which can store 2
the integration time under these conditions with WDIV = 0 is
calculated as
When WDIV is set to a value different from 0, the time before
overflow is scaled accordingly as shown in Equation 22.
Energy Accumulation Mode
The active power accumulated in each watt-hr accumulation
register (AWATTHR, BWATTHR, or CWATTHR) depends on
the configuration of the CONSEL bits in the COMPMODE
register (Bit 0 and Bit 1). The different configurations are
described in Table 10.
Table 10. Inputs to Watt-Hr Accumulation Registers
CONSEL[1, 0]
00
01
10
11
The contents of the watt-hr accumulation registers are affected
by both the current gain register (IGAIN) and the watt gain
register of the corresponding phase. IGAIN should not be used
when using Mode 0 of CONSEL, COMPMODE[1:0].
Depending on the poly phase meter service, the appropriate
formula should be chosen to calculate the active energy. The
American ANSI C12.10 Standard defines the different
configurations of the meter.
Table 11 describes which mode should be chosen in these
different configurations.
Table 11. Meter Form Configuration
5S/13S
6S/14S
8S/15S
9S/16S
ANSI Meter Form
Time = Time (WDIV = 0) × WDIV[7:0]
Time
=
3-Wire Delta
4-Wire Wye
4-Wire Delta
4-Wire Wye
0xFF,
0xCCCCD
40
AWATTHR
VA × IA
VA × (IA – IB)
VA × (IA – IB)
Reserved
FFFF,
− 1 or 0xFF, FFFF, FFFF before it overflows,
FFFF
CONSEL (d)
0
1
2
0
×
0.4
BWATTHR
VB × IB
0
0
Reserved
μs
=
0.524
15
TERMSEL (d)
3, 5, or 6
7
7
7
sec
− 1 or 0x7FFF.
CWATTHR
VC × IC
VC × (IC – IB)
VC × IC
Reserved
(21)
(22)
Rev. D | Page 33 of 72
Different gain calibration parameters are offered in the ADE7758
to cover the calibration of the meter in different configurations.
It should be noted that in CONSEL Mode 0d, the IGAIN and
WGAIN registers have the same effect on the end result. However,
changing IGAIN also changes all other calculations that use the
current waveform. In other words, changing IGAIN changes the
active, reactive, and apparent energy, as well as the rms current
calculation results. IGAIN should not be used when using Mode 0
of CONSEL COMPMODE[1:0].
Active Power Frequency Output
Pin 1 (APCF) of the ADE7758 provides frequency output for
the total active power. After initial calibration during manufac-
turing, the manufacturer or end customer often verifies the
energy meter calibration. One convenient way to verify the
meter calibration is for the manufacturer to provide an output
frequency that is proportional to the energy or active power
under steady load conditions. This output frequency can provide a
simple, single-wire, optically isolated interface to external
calibration equipment. Figure 68 illustrates the energy-to-
frequency conversion in the ADE7758.
A digital-to-frequency converter (DFC) is used to generate the
APCF pulse output from the total active power. The TERMSEL
bits (Bit 2 to Bit 4) of the COMPMODE register can be used to
select which phases to include in the total power calculation.
Setting Bit 2, Bit 3, and Bit 4 includes the input to the AWATTHR,
BWATTHR, and CWATTHR registers in the total active power
calculation. The total active power is signed addition. However,
setting the ABS bit (Bit 5) in the COMPMODE register enables
the absolute-only mode; that is, only the absolute value of the
active power is considered.
The output from the DFC is divided down by a pair of frequency
division registers before being sent to the APCF pulse output.
Namely, APCFDEN/APCFNUM pulses are needed at the DFC
output before the APCF pin outputs a pulse. Under steady load
conditions, the output frequency is directly proportional to the
total active power. The pulse width of APCF is 64/CLKIN if
APCFNUM and APCFDEN are both equal. If APCFDEN is
greater than APCFNUM, the pulse width depends on APCFDEN.
The pulse width in this case is T × (APCFDEN/2), where T is
the period of the APCF pulse and APCFDEN/2 is rounded to
the nearest whole number. An exception to this is when the
period is greater than 180 ms. In this case, the pulse width is
fixed at 90 ms.
INPUT TO AWATTHR
INPUT TO BWATTHR
INPUT TO CWATTHR
REGISTER
REGISTER
REGISTER
Figure 68. Active Power Frequency Output
+
+
+
DFC
APCFNUM[11:0]
APCFDEN[11:0]
÷
÷4
ADE7758
APCF