MAX71020 데이터 시트보기 (PDF) - Maxim Integrated

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MAX71020

Single-Chip Electricity Meter AFE

Maxim Integrated 

MAX71020

Single-Chip Electricity Meter AFE

Hardware Description

Hardware Overview

The MAX71020 energy meter analog front-end (AFE)

integrates all primary functional blocks required to imple-

ment a solid-state residential electricity meter. Included

on the chip are:

● An analog front-end (AFE) featuring a 22-bit second-

order sigma-delta ADC

● An independent 32-bit digital computation engine

(CE) to implement DSP functions

● A precision voltage reference (VREF)

● A temperature sensor for digital temperature

sensing and compensation

● Four I/O pins

● A zero-crossing detector with interrupt output

● Resistive shunt and current transformers

are supported

● A SPI slave for connection to a host controller

In a typical application, the 32-bit compute engine (CE)

of the MAX71020 sequentially processes the samples

from the voltage inputs on analog input pins and per-

forms calculations to measure active energy (Wh) and

reactive energy (VARh), as well as A2h, and V2h for

four-quadrant metering. These measurements are then

accessed by the host controller.

In addition to the temperature-trimmed ultra-precision

voltage reference, the on-chip digital temperature com-

pensation mechanism includes a temperature sensor

and associated controls for correction of unwanted

temperature effects on measurement, e.g., to meet the

requirements of ANSI and IEC standards.

Temperature-dependent external components such as

crystal oscillator, resistive shunts, current transformers

(CTs) and their corresponding signal conditioning circuits

can be characterized and their correction factors can be

programmed to produce electricity meters with excep-

tional accuracy over the industrial temperature range.

Communications with the host is conducted over a SPI

interface. The communications protocol between the host

and the MAX71020 provides a redundant information

transfer ensuring the correctness of commands trans-

ferred from the host to the AFE, and of data transferred

from the AFE to the host.

In addition, the MAX71020 has one pin dedicated as an

interrupt output to the host. This pin notifies the host of

asynchronous events.

Analog Section

Signal Input Pins

The MAX71020 has four analog inputs: two single-ended

inputs for voltage measurement, and two differential

inputs for current measurement.

The IAP, IAN, IBP, and IBN pins are current sensor

inputs. The differential inputs feature preamplifiers with

a selectable gain of 1 or 9, and are intended for direct

connection to a shunt resistor sensor or a current trans-

former (CT).

The voltage inputs in the MAX71020 are single-ended,

and are intended for sensing the line voltage via resistive

dividers. These single-ended inputs are referenced to

the GNDA pin.

All analog signal input pins measure voltage. In the

case of shunt current sensors, currents are sensed as a

voltage drop in the shunt resistor sensor. In the case of

Current Transformers (CT), the current is measured as a

voltage across a burden resistor that is connected to the

secondary winding of the CT. Meanwhile, line voltages

are sensed through resistive voltage-dividers.

Some versions of the device implement a preamplifier

with a fixed gain of 8.9 to enhance performance when

using sensors with a low-amplitude output (for example,

current shunts). When using a device with the preamplifi-

er enabled, the input signal amplitude cannot be greater

than 27.78mV peak.

Input Multiplexer

The input multiplexer sequentially applies the input signals

from the analog input pins to the input of the ADC. One

complete sampling sequence is called a multiplexer frame.

The IBP-IBN differential input may be used to sense the

neutral current, and VB may be optionally used to sense

a second voltage channel.This configuration implies that

the multiplexer applies a total of four inputs to the ADC.

For this configuration, the multiplexer sequence is as

shown in Figure 2. In this configuration IAP-IAN, IBP-IBN,

VA and VB are sampled. The physical current sensor for

the neutral current measurement and the voltage sensor

for VB may be omitted if not required.

Maxim Integrated

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