Datasheet

71M6515H

Energy Meter IC

DATA SHEET

JULY 2011

A Maxim Integrated Products Brand

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.

EQU

Watt & VAR Formula Application Channels used from MUX

sequence

Mux State:

0 1 2 3 4 5

0 VA IA 1 element, 2W 1ø IA VA - - - -

1* VA(IA-IB)/2 1 element, 3W 1ø IA VA IB - - -

2 VA IA + VB IB 2 element, 3W 3 øDelta IA VA IB VB - -

3* VA (IA - IB)/2 + VC IC 2 element, 4W 3ø Delta IA VA IB - IC VC

4* VA(IA-IB)/2 + VB(IC-IB)/2) 2 element, 4W 3ø Wye IA VA IB VB IC -

5 VA IA + VB IB + VC IC 3 element, 4W 3ø Wye IA VA IB 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.