71m6515h Maxim Integrated Products, Inc., 71m6515h Datasheet - Page 14

• Manufacturer Part Number: 71m6515h
• Description: 71m6515h Energy Meter Ic
• Manufacturer: Maxim Integrated Products, Inc.

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.
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, V
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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EQU
0
1
2
3
4
5
Watt & VAR Formula
(WSUM/VARSUM)
VA IA (1 element, 2W 1φ)
VA*(IA-IB)/2
(1 element, 3W 1φ)
VA*IA + VB*IB
(2 element, 3W 3φ Delta)
VA*(IA-IB)/2 + VC*IC
(2 element, 4W 3φ Delta)
VA*(IA-IB)/2 + VB*(IC-IB)/2
(2 element, 4W 3φ Wye)
VA*IA + VB*IB + VC*IC
(3 element, 4W 3φ Wye)
2
, and I
© 2005-2008 TERIDIAN Semiconductor Corporation
2
Table 2: Meter Element Output Mapping
and accumulates them for one interval.
VA*(IA-IB)/2
VA*(IA-IB)/2
VA*(IA-IB)/2
VAR0SUM
W0SUM/
VA*IA
VA*IA
VA*IA
DIGITAL COMPUTATION
ANALOG FRONT END
VB*(IC-IB)/2
VAR1SUM
W1SUM/
VA*IB
VB*IB
VB*IB
-
-
Element Output Mapping
VAR2SUM
W2SUM/
VC*IC
VC*IC
-
-
-
Energy Meter IC
IA-IB
IA-IB
IA-IB
I0SQ
SUM
IA
IA
IA
DATA SHEET
71M6515H
IC-IB
I1SQ
SUM
IB
IB
IB
IB
-
MARCH 2008
I2SQ
SUM
IC
IC
IC
-
-
-
V1.4