71M6515H Datasheet, PDF (14/57 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6515H
Energy Meter IC
DATA SHEET
MARCH 2008
Watt & VAR Formula
EQU
(WSUM/VARSUM)
0 VA IA (1 element, 2W 1φ)
1
VA*(IA-IB)/2
(1 element, 3W 1φ)
2
VA*IA + VB*IB
(2 element, 3W 3φ Delta)
3 _{VA*(IA-IB)/2 + VC*IC}
(2 element, 4W 3φ Delta)
4 _{VA*(IA-IB)/2 + VB*(IC-IB)/2}
(2 element, 4W 3φ Wye)
5 _{VA*IA + VB*IB + VC*IC}
(3 element, 4W 3φ Wye)
W0SUM/
VAR0SUM
VA*IA
VA*(IA-IB)/2
Element Output Mapping
W1SUM/
VAR1SUM
W2SUM/
VAR2SUM
I0SQ
SUM
-
-
IA
VA*IB
-
IA-IB
VA*IA
VB*IB
-
IA
VA*(IA-IB)/2
-
VC*IC
IA-IB
VA*(IA-IB)/2 VB*(IC-IB)/2
IA-IB
VA*IA
VB*IB
VC*IC
IA
Table 2: Meter Element Output Mapping
I1SQ
SUM
-
IB
IB
IB
IC-IB
IB
I2SQ
SUM
-
-
-
IC
IC
IC
ANALOG FRONT END
A/D Converter (ADC)
A single delta-sigma A/D converter (ADC) digitizes the inputs to the device. The resolution of the ADC is 21 bits. The ADC
operates at 5MHz oversampling rate and places the digital results in CE memory. Each analog input is sampled at 2520Hz.
Once each accumulation interval, it refreshes the temperature value that is placed in the TEMP_RAW register. The analog re-
ference for all inputs is V3P3A, i.e. the ADC processes voltages between the input pins and V3P3A.
Voltage Reference
The device includes an on-chip precision bandgap voltage reference that incorporates auto-zero techniques as well as
production trims to minimize errors caused by component mismatch and drift. The result is a voltage output with a predictable
temperature coefficient.
The CE compensates for temperature characteristics of the voltage reference by modifying the gain applied to the V and I
channels based on the coefficients PPMC and PPMC2. See the section “TEMPERATURE COMPENSATION” for details.
DIGITAL COMPUTATION
The six ADC outputs are processed and accumulated digitally. The default product summation is based on 42*60 (if the
SUM_CYCLES register is set to 60) samples per accumulation interval. At the end of each accumulation interval, a ready
interrupt (IRQZ) is signaled (if enabled with the READY bit in STMASK), indicating that fresh data is available to the host. For
instance, if SUM_CYCLES =30, the IRQZ rate will be 2Hz (500ms).
A dedicated 32-bit Computation Engine (CE) performs the precision computations necessary to accurately measure energy.
Internal CE calculations include frequency-insensitive offset cancellation on all six channels and a frequency insensitive 90°
phase shifter for VAR calculations. The CE also includes LPF smoothing filters after each product and squaring circuit to
attenuate ripple and eliminate beat frequencies between the power line fundamental and the accumulation time. The CE
directly calculates Watts, VARs, V², and I² and accumulates them for one interval.
At the end of each CE computation cycle, the accumulated data are post-processed to calculate RMS amplitudes, phase
angles, and VAh. When post-processing is complete, the IRQZ signal is activated.
The minimum combined cycle time for CE and post-processor is 400ms, which makes the maximum frequency for the IRQZ
signal 2.5Hz.
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