71M6515H
A Maxim Integrated Products Brand
Energy Meter IC
DATA SHEET
JULY 2011
FUNCTIONAL DESCRIPTION
THEORY OF OPERATION
The 71M6515H integrates the primary functional blocks required to implement a solid-state electricity meter front end. Included
on-chip are an analog front end (AFE), a digital computation engine (CE), a voltage reference, a real time clock, and I/O pins.
Various current sensor technologies are supported including Current Transformers (CT), Resistive Shunts, and Rogowski
(di/dt) Coils.
In a typical application, the 71M6515H sequentially digitizes the voltage inputs on pins IA, VA, IB, VB, IC, VC and performs
calculations to measure active energy (Wh), reactive energy (VARh), and apparent energy (VAh). In addition to these
measurement functions, the real time clock function allows the device to record time of use (TOU) metering information for
multi-rate applications.
The 71M6515H contains a temperature-trimmed ultra-precise voltage reference, and the on-chip digital temperature compen-
sation mechanism includes a temperature sensor and associated controls for correction of unwanted temperature effects on
measurement. RTC accuracy can be greatly improved by supplying correction coefficients derived from crystal
characterization. The combination of both features enables designers to produce electricity meters with exceptional accuracy
over the industrial temperature range.
Meter Equations
The 71M6515H implements the equations in Table 1. Register EQU specifies the equation to be used. In one sample time,
each of the six inputs is converted and the selected equation updated. In a typical application, IA, IB, IC are connected to
current transformers that sense the current on each phase of the line voltage. VA, VB, and VC are typically connected to
voltage sensors (resistor dividers) with respect to NEUTRAL. NEUTRAL is to be connected to V3P3A, the analog supply
voltage. NEUTRAL is the zero reference for all analog measurements.
Watt & VAR Formula
Application
Channels used from MUX
sequence
EQU
Mux State:
0
1
2
3
-
4
-
5
-
0
1*
2
VA IA
1 element, 2W 1ø
IA
IA
IA
IA
IA
IA
VA
VA
VA
VA
VA
VA
-
VA(IA-IB)/2
1 element, 3W 1ø
IB
IB
IB
IB
IB
-
-
-
VA IA + VB IB
2 element, 3W 3 øDelta
2 element, 4W 3ø Delta
2 element, 4W 3ø Wye
3 element, 4W 3ø Wye
VB
-
-
-
3*
4*
5
VA (IA - IB)/2 + VC IC
VA(IA-IB)/2 + VB(IC-IB)/2)
VA IA + VB IB + VC IC
IC VC
VB IC
-
VB IC VC
Note: Equations 1*, 3*, 4* available only when IMAGE = 00 (CT mode).
Table 1: Meter Equations
Table 2 shows how the elements of the meter are mapped for the six possible equations.
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