MAX71020AEUI-R(2012) データシートの表示（PDF） - Maxim Integrated
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MAX71020AEUI-R Datasheet PDF : 37 Pages
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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
compensation
● Four I/O pins
● A zero-crossing interrupt
● Resistive shunt and current transformers
are supported
● A SPI slave for connection to a host microcontroller
In a typical application, the 32-bit compute engine (CE)
of the MAX71020 sequentially processes the samples
from the voltage inputs on analog input pinsand performs
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 microcontroller.
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. In this way, the MAX71020
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.
IAP, IAN, IBP, and IBN pins are current sensor inputs.
The differential inputs feature preamplifiers with a select-
able gain of 1 or 9, and are intended for direct connection
to a shunt resistor sensor or a current transformer (CT).
The voltage inputs in the MAX71020 are single-ended,
and are intended for sensing the line voltage. 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. Voltage
inputs are single-ended and their common return is the
GNDA pin.
Some versions of the device implement a preamplifier
with a fixed gain of 9 to enhance performance when
using sensors with a low-amplitude output (for example,
current shunts). When using a device with the preampli-
fier enabled, you must ensure that the input amplitude is
no 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 1. 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.
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