Программируемые логические контроллеры (ПЛК) и распределенные системы управления (РСУ)

AD5758 - это одноканальный цифро-аналоговый преобразователь (ЦАП) с выходом тока и напряжения, который работает от напряжения питания в диапазоне от -33 В (минимум) на выводе AVSS до +33 В (максимум) на выводе AVDD1 при максимальной разнице между двумя напряжениями 60 В. Интегрированная схема динамического управления энергопотреблением минимизирует мощность, рассеиваемую корпусом, за счет регулировки напряжения питания (V_DPC+), подаваемого на схему выходного драйвера VI_OUT, в диапазоне от 5 В до 27 В при помощи понижающего импульсного преобразователя постоянного напряжения. Вывод C_HART позволяет добавлять сигналы протокола HART^® к выходному току.

Компонент имеет универсальный четырехпроводной последовательный интерфейс, который работает с частотой тактового сигнала до 50 МГц и совместим со стандартными интерфейсами SPI, QSPITM, MICROWIRETM, а также другими интерфейсами цифровых сигнальных процессоров и микроконтроллеров. Интерфейс также обеспечивает опциональную проверку на наличие ошибок в пакете при помощи циклического кода с избыточностью и имеет сторожевой таймер. По сравнению со своими предшественниками AD5758 имеет расширенные функции диагностики, включая схему мониторинга выходного тока и интегрированный 12-разрядный диагностический аналого-цифровой преобразователь (АЦП). Интеграция защитных ключей на выводах VI_OUT, +V_SENSE и −V_SENSE повышает отказоустойчивость компонента. При совместном использовании с микросхемой управления питанием/изолятором ADP1031 компонент позволяет пользователям реализовать восьмиканальный модуль аналогового вывода с межканальной гальванической развязкой, имеющий рассеиваемую мощность менее 2 Вт и удовлетворяющий требованиям CISPR 11 Class B

Ключевые особенности продукта

1. Динамическое управление энергопотреблением при помощи интегрированного понижающего преобразователя постоянного напряжения для уменьшения рассеиваемого тепла. При совместном использовании с микросхемой ADP1031 компонент позволяет реализовать восьмиканальный модуль аналогового вывода с межканальной гальванической развязкой, имеющий рассеиваемую мощность менее 2 Вт
2. Ряд диагностических функций, включая интегрированный АЦП
3. Высокая отказоустойчивость, защита выходных цепей от неправильного подключения (±38 В)
4. Совместимость с протоколом HART

Области применения

• Управление технологическими процессами
• Управление приводами
• Модули аналогового вывода с гальванической развязкой каналов
• Программируемые логические контроллеры и распределенные системы управления
• Системы, работающие по протоколу HART

The ADP1031 is a high performance, isolated micropower management unit (PMU) that combines an isolated flyback dc-to-dc regulator, an inverting dc-to-dc regulator, and a buck dc-to-dc regulator, providing three isolated power rails. Additionally, the ADP1031 contains four, high speed, serial peripheral interface (SPI) isolation channels and three general-purpose isolators for channel to channel applications where low power dissipation and small solution size is required.

Operating over an input voltage range of +4.5 V to +60 V, the ADP1031 generates isolated output voltages of +6 V to +28 V (adjustable version) or+ 21 V and +24 V (fixed versions) for V_OUT1, factory programmable voltages of +5.15 V, +5.0 V, or +3.3 V for V_OUT2, and an adjustable output voltages of −24 V to −5 V for V_OUT3.

By default, the ADP1031 flyback regulator operates at a 250 kHz switching frequency and the buck and inverting regulators operate at 125 kHz. All three regulators are phase shifted relative to each other to reduce electromagnetic interference (EMI). The ADP1031 can be driven by an external oscillator in the range of 350 kHz to 750 kHz to ease noise filtering in sensitive applications.

The digital isolators integrated in the ADP1031 use Analog Devices, Inc., iCoupler^® chip scale transformer technology, optimized for low power and low radiated emissions.

The ADP1031 is available in a 9 mm × 7 mm, 41-lead LFCSP and is rated for a −40°C to +125°C operating junction temperature range.

Applications

• Industrial automation and process control
• Instrumentation and data acquisition systems
• Data and power isolation

AD7124-4 – это обладающий низким шумом и малым энергопотреблением, полностью интегрированный аналоговый входной интерфейс для задач прецизионного измерения. Компонент содержит 24-разрядный Σ-Δ аналого-цифровой преобразователь (АЦП) с низким шумом и может быть сконфигурирован для работы с 4 дифференциальными или 7 несииметричными/псевдодифференциальными входными сигналами. Интегрированный усилительный каскад с малым коэффициентом усиления позволяет подавать слабые сигналы непосредственно на АЦП.

Одно из основных преимуществ AD7124-4 заключается в том, что компонент дает пользователю возможность выбрать один из трех интегрированных режимов энергопотребления. Выбранный режим определяет потребляемый ток, диапазон скоростей обновления выходных данных и среднеквадратическое значение шума. Компонент также имеет несколько вариантов фильтрации, что позволяет пользователю получить максимальную степень свободы проектирования.

AD7124-4 способен поддерживать одновременное подавление помех на частотах 50 Гц и 60 Гц при работе с частотой обновления выходных данных 25 SPS (установление сигнала за один цикл). При понижении частоты обновления можно достичь подавления более 80 дБ.

AD7124-4 обеспечивает наивысшую степень интеграции сигнальной цепочки. Компонент содержит прецизионный, малощумящий источник опорного напряжения с малым дрейфом, а также поддерживает работу с внешним дифференциальным опорным напряжением, которое может быть буферизировано внутреннем буфером. К другим ключевым интегрированным блокам компонента относятся программируемые источники тока возбуждения с малым дрейфом, источники диагностических токов, а также генератор напряжения смещения, который устанавливает синфазное напряжение канала равным AVDD/2. Ключ цепи низкого напряжения питания позволяет пользователям отключать питание мостовых датчиков в интервалах между преобразованиями, гарантируя минимальную потребляемую системой мощность. Компонент также даёт пользователю возможность выбора между внутренним и внешним источником тактового сигнала.

Интегрированный блок управления последовательностью преобразования позволяет пользователю выбирать несколько каналов AD7124-4 для автоматического последовательного преобразования, упрощая обмен данными с компонентом. Одновременно может быть активно до 16 каналов, включая как каналы аналоговых входных сигналов, так и диагностические каналы, например, каналы контроля уровней напряжения питания или опорного напряжения. Эта уникальная особенность позволяет чередовать диагностику с преобразованиями сигналов внешних источников.

AD7124-4 поддерживает независимое конфигурирование каждого отдельного канала. Компонент позволяет реализовать до восьми конфигурационных настроек. Каждая конфигурация включает в себя опции коэффициента усиления, типа фильтра, частоты обновления выходных данных, буферизации и источника опорного напряжения. Пользователь может назначать любую из этих конфигураций любому из каналов в произвольном порядке.

AD7124-4 также обладает обширными возможностями функциональной диагностики, позволяющими повысить устойчивость решения. Они включают в себя проверку данных с использованием контрольной суммы (CRC), проверки сигнальной цепочки и проверки работоспособности последовательного интерфейса. Эти диагностические функции уменьшают число внешних компонентов, необходимых для реализации диагностики, сокращая требуемое пространство на печатной плате, время проектирования и стоимость. Значение доли безопасных отказов (SFF), показанное в тесте FMEDA (анализ видов, эффектов и диагностики отказов) типичного приложения, превышает 90% в соответствии с IEC 61508.

Компонент работает с однополярным напряжением питания аналоговой части в диапазоне от 2.7 В до 3.6 В или биполярным напряжением 1.8 В. Напряжение питания цифровой части имеет допустимый диапазон от 1.65 В до 3.6 В. Гарантированный рабочий температурный диапазон составляет от −40°C до +105°C. AD7124-4 выпускается в 32-выводном корпусе LFCSP и 24-выводном корпусе TSSOP.

Обратите внимание, что при ссылке на многофункциональные выводы, например, DOUT/RDY в техническом описании может указываться как полное имя вывода, так и только имя отдельной обсуждаемой функции, например, RDY.

Области применения

• Измерение температуры
• Измерение давления
• Управление промышленными процессами
• Измерительные приборы
• Интеллектуальные передатчики 

AD7124-8 - это обладающий низким шумом, малопотребляющий, полностью интегрированный аналоговый входной интерфейс для прецизионных измерений. Компонент включает в себя 24-разрядный Σ-Δ АЦП с низким шумом, который может быть сконфигурирован для работы с 8 дифференциальными входными сигналами или 15 несимметричными, либо псевдодифференциальными входными сигналами. Интегрированный каскад с малым коэффициентом усиления позволяет подавать сигналы непосредственно на АЦП.

Одним из основных достоинств AD7124-8 является возможность выбора пользователем одного из трех интегрированных режимов энергопотребления. Выбранный режим определяет уровень потребляемого тока, диапазон скоростей выходных данных и среднеквадратический уровень шума. Компонент также имеет ряд опций фильтрации, что дает пользователю максимальную степень свободы при проектировании.

AD7124-8 может обеспечивать одновременное подавление помех на частотах 50 Гц и 60 Гц при работе с частотой обновления выходных данных 25 SPS (установление сигнала за один такт); при меньших частотах выходных данных подавление может достигать более 80 дБ.

AD7124-8 обеспечивает наивысшую степень интеграции сигнального тракта. Компонент содержит прецизионный внутренний источник опорного напряжения с низким шумом и малым дрейфом на запрещенной зоне, а также поддерживает работу с внешним дифференциальным опорным напряжением, которое может буферизироваться внутренним буфером. К другим ключевым интегрированным функциям компонента относятся программируемые источники тока возбуждения с малым дрейфом, источники диагностических токов и генератор напряжения смещения, при помощи которого синфазное напряжение канала устанавливается равным AV_DD/2. Ключ цепи низкого напряжения питания позволяет пользователю отключать мостовые датчики в интервалах между преобразованиями, гарантируя абсолютное минимальное потребление мощности системой. Компонент также позволяет пользователю выбирать между внутренним или внешним тактовом сигналом.

Интегрированный модуль управления последовательностью каналов позволяет пользователю выбирать несколько активных каналов, в которых AD7124-8 будет последовательно выполнять преобразования, упрощая взаимодействие с компонентом. Одновременно может быть активировано до 16 каналов, которыми могут быть как каналы аналоговых входных сигналов, так и диагностические каналы, например, канал проверки напряжения питания или опорного напряжения. Эта уникальная возможность позволяет чередовать диагностику с преобразованиями. AD7124-8 также поддерживает конфигурирование каналов в индивидуальном порядке. Компонент имеет восемь готовых конфигурационных настроек, каждая из которых задаёт определённую комбинацию коэффициента усиления, типа фильтра, частоты выходных данных, буферизации и источника опорного напряжения. Пользователь может назначить каналу любую из этих конфигураций в индивидуальном порядке.

AD7124-8 также имеет обширные возможности диагностики, включая проверку контрольной суммы (CRC), поверки сигнального тракта и проверки последовательного интерфейса, за счёт чего достигается повышенная надёжность решения. Эти диагностические функции сокращают количество внешних компонентов, необходимых для реализации диагностики, позволяя сэкономить пространство на печатной плате, ускорить проектирование и снизить стоимость. Для безопасных отказов в тестах FMEDA для типичного приложения составила более 90% в соответствии с IEC 61508.

Компонент работает с однополярным питанием аналоговой части в диапазоне от 2.7 В до 3.6 В или биполярным питанием 1.8 В. Напряжение питания цифровой части имеет допустимый диапазон от 1.65 В до 3.6 В. Рабочий температурный диапазон составляет от −40°C до +105°C. AD7124-8 выпускается в 32-выводном корпусе LFCSP.

Обратите внимание, что обозначение многофункциональных выводов в техническом описании, например, DOUT/RDY, может даваться либо целиком, либо только именем отдельной функции, обсуждаемой в конкретно взятом случае, например, RDY.

Области применения

• Измерение температуры
• Измерение давления
• Управление промышленными технологическими процессами
• Измерительные приборы
• Интеллектуальные передатчики

The fido5100 and fido5200 (REM switch) are programmable IEEE 802.3 10 Mbps/100 Mbps Ethernet Internet Protocol Version 6 (IPv6) and Internet Protocol Version 4 (IPv4) switches that support virtually any Layer 2 or Layer 3 protocol. The switches are personalized to support the desired protocol by firmware that is downloaded from a host processor.

The firmware is contained in the real-time Ethernet multiprotocol (REM) switch driver and is downloaded at power-up. The REM switch can be ready for network data operation in less than 4 ms to support fast startup and quick connect type network functionality. The REM switch devices have the same signal assignments as defined in this data sheet.

The fido5100 supports the following protocols: PROFINET real time (RT) and isochronous real time (IRT), EtherNet/IP with and without device level ring (DLR), Modbus TCP, and POWERLINK.

The fido5200 supports the following protocols: EtherCAT and all protocols defined for the fido5100.

The REM switch is intended for use with a host processor. Network operation is handled using the functions and services provided in the REM switch driver. The host processor can implement any protocol stack by integrating it with the REM switch driver. An example application is shown in Figure 11.

The REM switches are available in a 144-ball chip scale package ball grid array (CSP_BGA) package.

Note that throughout this data sheet, multifunction pins, such as A02/ALE, are referred to either by the entire pin name or by a single function of the pin, for example, ALE, when only that function is relevant.

Applications

• Industrial automation
  
  • Process control
  • Managed Ethernet switch

The fido5100 and fido5200 (REM switch) are programmable IEEE 802.3 10 Mbps/100 Mbps Ethernet Internet Protocol Version 6 (IPv6) and Internet Protocol Version 4 (IPv4) switches that support virtually any Layer 2 or Layer 3 protocol. The switches are personalized to support the desired protocol by firmware that is downloaded from a host processor.

The firmware is contained in the real-time Ethernet multiprotocol (REM) switch driver and is downloaded at power-up. The REM switch can be ready for network data operation in less than 4 ms to support fast startup and quick connect type network functionality. The REM switch devices have the same signal assignments as defined in this data sheet.

The fido5100 supports the following protocols: PROFINET real time (RT) and isochronous real time (IRT), EtherNet/IP with and without device level ring (DLR), Modbus TCP, and POWERLINK.

The fido5200 supports the following protocols: EtherCAT and all protocols defined for the fido5100.

The REM switch is intended for use with a host processor. Network operation is handled using the functions and services provided in the REM switch driver. The host processor can implement any protocol stack by integrating it with the REM switch driver. An example application is shown in Figure 11.

The REM switches are available in a 144-ball chip scale package ball grid array (CSP_BGA) package.

Note that throughout this data sheet, multifunction pins, such as A02/ALE, are referred to either by the entire pin name or by a single function of the pin, for example, ALE, when only that function is relevant.

Applications

• Industrial automation
  
  • Process control
  • Managed Ethernet switch

The circuit shown in Figure 1 provides a full function, flexible, programmable analog output solution with only two analog components and meets most requirements for programmable logic controller (PLC) and distributed control system (DCS) applications. The AD5660-1 low power (2.8 mW @ 5 V), rail-torail output, 16-bit nanoDAC^®, combined with the AD5750-1 industrial current/voltage output driver, provides all the typical current and voltage output ranges with 16-bit resolution and no missing codes, 0.05% linearity, and less than 0.1% output error. The circuit also contains key features for industrial applications, such as on-chip output fault detection, CRC checking to prevent packet error (PEC), and flexible power-up options, making it an ideal choice for robust industrial control systems. No external precision resistors or calibration routines are needed to maintain consistent performance in mass production, thereby making it ideal for PLC or DCS modules.

The circuit, shown in Figure 1, is a complete analog front end for digitizing ±10 V industrial level signals with a 16-bit differential input PulSAR^® ADC. The circuit provides a high impedance instrumentation amplifier input with high CMR, level shifting, attenuation, and differential conversion, with only two analog components. Because of the high level of integration, the circuit saves printed circuit board space and offers a cost effective solution for a popular industrial application.

Signal levels of up to ±10 V are typical in process control and industrial automation systems. With smaller signal inputs from sensors such as thermocouples and load cells, large commonmode voltage swings are often encountered. This requires a flexible analog input that handles both large and small differential signals with high common-mode rejection and also has a high impedance input.

Attenuation and level shifting are necessary to process industrial level signals with modern low voltage ADCs. In addition, fully differential input ADCs offer the advantages of good common-mode rejection, reduction in second-order distortion products, and simplified dc trim algorithms. Industrial signals, therefore, need further conditioning to properly interface with differential input ADCs.

The circuit in Figure 1 is a complete and highly integrated analog front end industrial level signal conditioner that uses only two active components to drive an AD7687 differential input 16-bit PulSAR ADC: the AD8295 precision in-amp (with two on-chip auxiliary op amps) and the AD8275 level translator/ADC driver. An ADR431 low noise 2.5V XFET^® reference supplies the voltage reference for the ADC.

The AD8295 is a precision instrumentation amplifier with two uncommitted on-chip signal processing amplifiers and two precisely matched 20 kΩ resistors in a small 4 mm × 4 mm package.

The AD8275 is a G = 0.2 difference amplifier that can be used to attenuate ±10 V industrial signals, and the attenuated signal can be easily interfaced to a single supply low voltage ADC. The AD8275 performs the attenuation and level shifting function in the circuit, maintaining good CMR without any need for external components.

The AD7687 is a 16-bit, successive approximation ADC that operates from a single power supply between 2.3 V and 5.5 V. It has a differential input for good CMR and also offers the ease of use associated with SAR ADCs.

The circuit shown in Figure 1 is a completely isolated 12-bit, 300 kSPS RTD temperature measuring system that uses only three active devices. The system processes the output of a Pt100 RTD and includes an innovative circuit for lead-wire compensation using a standard 3-wire connection. The circuit operates on a single 3.3 V supply. The total error after room temperature calibration is less than ±0.24% FSR for a ±10°C change in temperature, making it ideal for a wide variety of industrial temperature measurements.

The small footprint of the circuit makes this combination an industry-leading solution for temperature measurements where accuracy, cost, and size play a critical role. Both data and power are isolated, thereby making the circuit robust to high voltages and also ground-loop interference often encountered in harsh industrial environments.

The novel circuit for 3-wire RTD lead wire compensation was developed by Hristo Ivanov Gigov, Associate Professor and PhD, and Stanimir Krasimirov Stankov, Engineer and PhD Student, Department of Electronic Engineering and Microelectronics, Technical University of Varna, Varna, Bulgaria.

The circuit shown in Figure 1 provides a unique power saving solution for a digital-to-analog converter (DAC)-based, 4 mA to 20 mA output circuit. To provide sufficient headroom for typical resistive loads between 10 Ω and 1000 Ω, traditional 4 mA to 20 mA output driver stages must operate on at least 20 V (plus some additional headroom) to provide a sufficient voltage to drive high value resistive loads. For low value resistive loads, however, the fixed value, high voltage supply results in significant internal power dissipation that can affect DAC accuracy and require additional heat sinking.

The AD5755 quad 16-bit DAC has four independent high efficiency, internal dc-to-dc converters that drive the four output stages at a dynamically adjusted boost voltage based on sensing the actual output voltage of the 4 mA to 20 mA driver. The boost circuit maintains several volts of headroom on the output stage, regardless of the load resistance, thereby reducing the maximum internal power dissipation by a factor of approximately 4× for a 24 mA output current into a 10 Ω load.

The internal dc-to-dc converters require an external 5 V supply and can draw significant currents when the DAC outputs full-scale slew. A high efficiency external dc-to-dc converter circuit based on the ADP2300 is driven from the 15 V and supplies this voltage. The ADP2300 has excellent transient response to large current steps up to 800 mA and ensures proper operation of the boost converters as well as eliminating the need for a separate 5 V supply.

The entire circuit operates on ±15 V supplies that allow the DAC to provide voltage outputs that cover the industrial signal level range of up to ±10 V in addition to the 4 mA to 20 mA outputs. This combination of parts is a low cost, power efficient solution that minimizes the number of external components required and that ensures 16-bit performance for varying load conditions.

This circuit provides a complete, fully isolated, analog output channel suitable for programmable logic controllers (PLCs) and distributed control system (DCS) modules that require standard 4 mA to 20 mA HART^®1-compatible current outputs and unipolar or bipolar output voltage ranges. It provides a flexible building block for channel-to-channel isolated PLC/DCS output modules or any other industrial application that requires a fully isolated analog output. The circuit also includes external protection on the analog output terminals.

The AD5422 16-bit digital-to-analog converter (DAC) is software configurable and provides all the necessary current and voltage outputs.

The AD5700-1, the industry’s lowest power and smallest footprint HART-compliant IC modem, is used in conjunction with the AD5422 to form a complete HART-compatible 4 mA to 20 mA solution. The AD5700-1 includes a precision internal oscillator that provides additional space savings, especially in channel-to-channel isolated applications.

PLC/DCS solutions must be isolated from the local system controller to protect against ground loops and to ensure robustness against external events. Traditional solutions use discrete ICs for both power and digital isolation. When multichannel isolation is needed, the cost and space of providing discrete power solutions becomes a big disadvantage. Solutions based on optoisolators typically have reasonable output regulation but require additional external components, thereby increasing board area. Power modules are often bulky and can provide poor output regulation. The circuit in Figure 1 uses the ADuM347x family of isolators and power regulation circuitry along with associated feedback isolation. External transformers are used to transfer power across the isolation barrier.

The ADuM3482 provides the UART signal isolation for the AD5700-1.

The ADP2441, 36 V step-down dc-to-dc regulator, accepts an industrial standard 24 V supply, with wide tolerance on the input voltage. It steps this down to 5 V to power all controller side circuitry. The circuit also includes standard external protection on the 24 V supply terminals, as well as protection against dc overvoltage of +36 V down to −28 V.

¹ HART is a registered trademark of the HART Communication Foundation.

The circuit in Figure 1 provides 16-bit fully isolated ±10 V and 4 mA-to-20 mA outputs suitable for programmable logic controllers (PLCs) and distributed control systems (DCSs).

The circuit uses digital isolation, as well as PWM-controlled power regulation circuitry along with associated feedback isolation. External transformers are used to transfer power across the isolation barrier, and the entire circuit operates on a single +5 V supply located on the primary side. This solution is superior to isolated power modules, which are often bulky and may provide poor output regulation.

Digital isolators are superior to opto-isolators especially when multichannel isolation is needed. The integrated design isolates the circuit from the local system controller to protect against ground loops and also to ensure robustness against external events often encountered in harsh industrial environments.

The circuit shown in Figure 1 uses the AD5700, the industry’s lowest power and smallest footprint HART¹-compliant IC modem and the AD5420, a 16-bit current-output DAC, to form a complete HART-compatible 4 mA to 20 mA solution.

For additional space savings, the AD5700-1 offers a 0.5% precision internal oscillator.

This circuit adheres to the HART physical layer specifications as defined by the HART Communication Foundation, for example, the analog rate of change and noise during silence specifications.

For many years, 4 mA to 20 mA communication has been used in process control instrumentation. This communication method is reliable and robust, and offers high immunity to environmental interference over long communication distances. A limitation, however, is that only 1-way communication of one process variable at a time is possible.

The development of the highway addressable remote transducer (HART) standard provided highly capable 2-way digital communication, simultaneously with the 4 mA to 20 mA analog signaling used by traditional instrumentation equipment. This allows for features such as remote calibration, fault interrogation, and transmission of additional process variables. Put simply, HART is a digital two-way communication in which a 1 mA peak-to-peak frequency-shift-keyed (FSK) signal is modulated on top of the 4 mA to 20 mA analog current signal.

The circuit shown in Figure 1 is a multichannel, flexible, analog output solution with only two analog components and meets most requirements for multichannel I/O cards, programmable logic controllers (PLCs), and distributed control systems (DCSs) applications. The AD5686R quad, 16-bit nanoDAC+ with rail-to-rail buffered outputs combined with four of the AD5750-2 industrial current/voltage output drivers provide all the typical output current and voltage ranges with 16-bit resolution, no missing codes, 0.05% linearity, and less than 0.1% output error.

An ultralow drift (2 ppm/°C typical), 2.5 V voltage reference with high drive capability (up to ±5 mA) is integrated in the AD5686R and provides the reference voltage for both the AD5686R and the AD5750-2. This guarantees low noise, high accuracy, and low temperature drift for the circuit.

The ADuM1301 and ADuM5400 provide 2500 V rms isolation both on power, and all the necessary signals between the analog signal chain and the host controller.

For multichannel I/O card applications that need more than 4 channels, several AD5686Rs can be connected in a daisy chain, and no additional external digital I/O circuits are required. This minimizes the cost, especially for high channel count isolated applications.

The circuit also contains key features for industrial applications, such as on-chip output fault detection, packet error checking (PEC) by the CRC, flexible power-up options, and ESD protection (4 kV for the AD5686R, human body model and 3 kV for the AD5750-2, human body model), making it an ideal choice for robust industrial control systems. No external precision resistors or calibration routines are needed to maintain consistent performance in mass production, thereby making it ideal for PLC or DCS modules.

The circuit shown in Figure 1 is a flexible current transmitter that converts the differential voltage output from a pressure sensor to a 4 mA-to-20 mA current output.

The circuit is optimized for a wide variety of bridge-based voltage or current driven pressure sensors, utilizes only five active devices, and has a total unadjusted error of less than 1%. The power supply voltage can range from 7 V to 36 V depending on the component and sensor driver configuration.

The input of the circuit is protected for ESD and voltages beyond the supply rail, making it ideal for industrial applications.

The circuit shown in Figure 1 is a completely isolated 4-channel temperature measurement circuit optimized for performance, input flexibility, robustness, and low cost. It supports all types of thermocouples with cold junction compensation and any type of RTD (resistance temperature detector) with resistances up to 4 kΩ for 2-, 3-, or 4-wire connection configurations.

The RTD excitation current are is programmable for optimum noise and linearity performance.

RTD measurements achieve 0.1°C accuracy (typical), and Type-K thermocouple measurements achieve 0.05°C typical accuracy because of the 16-bit ADT7310 digital temperature sensor used for cold-junction compensation. The circuit uses a four-channel AD7193 24-bit sigma-delta ADC with on-chip PGA for high accuracy and low noise.

Input transient and overvoltage protection are provided by low leakage transient voltage supressors (TVS) and Schottky diodes. The SPI-compatible digital inputs and outputs are isolated (2500 V rms), and the circuit is operated on a fully isolated power supply.

Figure 1. 4-Channel Thermocouple and RTD Circuit (Simplified Schematic: All Connections and Decoupling Not Shown)

The circuit shown in Figure 1 uses the AD5700, the industry’s lowest power and smallest footprint HART^®1-compliant IC modem, and the AD5422, a 16-bit current output and voltage output DAC, to form a complete HART-compatible 4 mA to 20 mA solution. The use of the OP184 in the circuit allows the I_OUT and V_OUT pins to be shorted together, thus reducing the number of screw connections required in programmable logic control (PLC) module applications. For additional space savings, the AD5700-1 offers a 0.5% precision internal oscillator.

Application Note AN-1065 describes a manner in which the AD5420 I_OUT DAC can be configured for HART communication compliance. AN-1065 outlines how the AD5700 HART modem output can be attenuated and ac coupled into the AD5420 via the CAP2 pin. The same is true of the AD5422. However, if the application involves a particularly harsh environment, an alternative circuit configuration can be used which offers better power supply rejection characteristics. This alternative circuit requires the use of the external R_SET resistor and involves coupling the HART signal into the R_SET pin of the AD5420 or AD5422. The CN-0270 describes this solution for the AD5420, typical of line-powered transmitter applications. The current circuit note is relevant to the AD5422, which, unlike the AD5420, offers both a voltage and a current output pin, and so is particularly useful in PLC/distributed control system (DCS) applications. The AD5422 is available in both 40-lead LFCSP and 24-lead TSSOP packages and the relevance of this, to the circuit characteristics, is examined in the Circuit Description section.

This circuit adheres to the HART physical layer specifications as defined by the HART Communication Foundation, for example, the output noise during silence and the analog rate of change specifications.

For many years, 4 mA to 20 mA communication has been used in process control instrumentation. This communication method is reliable and robust, and offers high immunity to environmental interference over long communication distances. A limitation, however, is that only 1-way communication of one process variable at a time is possible.

The development of the highway addressable remote transducer (HART) standard provided highly capable 2-way digital communication, simultaneously with the 4 mA to 20 mA analog signaling used by traditional instrumentation equipment. This allows for features such as remote calibration, fault interrogation, and transmission of additional process variables. Put simply, HART is a digital two-way communication in which a 1 mA peak-to-peak, frequency-shift-keyed (FSK) signal is modulated on top of the 4 mA to 20 mA analog current signal.

The circuit shown in Figure 1 is a completely isolated 12-bit, 300 kSPS data acquisition system utilizing only three active devices.

The system processes ±10 V input signals using a single 3.3 V supply. The total error after room temperature calibration is less than ±0.1% FSR over a ±10°C temperature change, making it ideal for a wide variety of industrial measurements.

The small footprint of the circuit makes this combination an industry-leading solution for data acquisition systems where the accuracy, speed, cost, and size play a critical role. Both data and power are isolated, thereby making the circuit robust to high voltages and also ground-loop interference often encountered in harsh industrial environments.

The circuit in Figure 1 is a complete single-supply,16-bit buffered voltage output DAC that maintains ±1 LSB integral and differential nonlinearity by utilizing a CMOS DAC followed by an innovative amplifier that has no crossover distortion.

The circuit eliminates the crossover nonlinearity associated with most rail-to-rail op amps that can be as high as 4 or 5 LSBs for a 16-bit system.

This industry-leading solution is ideal for industrial process control and instrumentation applications where a compact, single-supply, low cost, and highly linear 16-bit buffered voltage source is required.

Total power dissipation for the three active devices is less than 25 mW typical when operating on a single 6 V supply. 

Figure 1. ±1 LSB Linear 16-Bit Buffered Voltage Output DAC (Simplified Schematic, All Connections and Decoupling Not Shown)

The system processes 4 mA to 20 mA input signals using a single 3.3 V supply. The total error after room temperature calibration is ±0.06% FSR over a ±10°C temperature change, making it ideal for a wide variety of industrial measurements.

The small footprint of the circuit makes this combination an industry-leading solution for 4 mA to 20 mA data acquisition systems where the accuracy, speed, cost, and size play a critical role. Both data and power are isolated, thereby making the circuit robust to high voltages and also ground-loop interference often encountered in harsh industrial environments.

The circuit shown in Figure 1 provides a complete, fully isolated, highly flexible, quad channel analog input system suitable for programmable logic controllers (PLCs) and distributed control system (DCS) applications that require multiple voltage inputs and HART-compatible, 4 mA to 20 mA current inputs.

The analog input circuit is designed for group isolated industrial analog inputs and can support voltage and current input ranges including ±5 V, ±10 V, 0 V to +5 V, 0 V to +10 V, +4 mA to +20 mA, and 0 mA to +20 mA.

The circuit is powered from a standard 24 V bus supply and generates an isolated 5 V system supply voltage.

In power line measurement and protection systems, there is a requirement to simultaneously sample large numbers of current and voltage channels of multiphase power distribution and transmission networks. In these applications, the channel count can vary from as few as six channels to greater than 64 channels. The AD7606 8-channel data acquisition system (DAS) with 16-bit bipolar simultaneously sampling SAR ADCs with on-chip overvoltage protection greatly simplifies signal condi-tioning circuitry and reduces the overall parts count, board real estate, and cost of the measurement and protection board. Even with its high level of integration, each AD7606 requires only nine low value ceramic decoupling capacitors.

n measurement and protection systems, simultaneous sampling capability is needed to maintain the phase information between the current and voltage channels on multiphase power line networks. The wide dynamic range capability of the AD7606 makes it ideal for capturing both under voltage/current and over voltage/current conditions. The input voltage range is pin-programmable for either ±5 V or ±10 V.

This circuit note describes details of the recommended PC board layout for applications using multiple AD7606 devices. The layout is optimized for channel-to-channel matching and part-to-part matching and will help reduce the complexity of calibration routines in high channel count systems. The circuit provides the ability to use the AD7606 2.5 V internal reference when channel-to-channel matching is important or an external ADR421 precision high accuracy (B grade: ±1 mV max), low drift (B grade: 3 ppm/°C max), low noise (1.75 μV p-p, typical, 0.1 Hz to 10 Hz) reference for high channel applications that require excellent absolute accuracy. The low noise and the stability and accuracy characteristics of the ADR421 make it ideal for high precision conversion applications. The combination of the two devices yields a level of integration, channel density, and accuracy that is unsurpassed in the industry.

With single-ended signaling, one wire from the signal source is routed throughout the system to the data acquisition interface. The voltage measured is the difference between the signal and the ground. Unfortunately, “ground” can be a different level in different places because the ground impedance can never be zero. This can lead to errors when using single-ended inputs, especially where the signal trace is long and grounds currents contain large digital transients. Single-ended signal runs are sensitive to noise pickup because they act as an antenna, picking up electrical activity. With single-ended inputs there is no way of distinguishing between the signal and the interfering noise. Most of the ground and noise problems are solved by differential signaling.

With differential signaling, two signal wires run from the signal source to the data acquisition interface. This can solve both of the problems caused by single-ended connections. Noise between the sending and receiving ground planes acts as a common-mode signal and is, therefore, greatly attenuated. The use of twisted pair wire causes noise pickup to appear as a common-mode signal, which is also greatly attenuated at the receiver. Another advantage of differential transmission is that the differential signal has twice the amplitude of the equivalent single-ended signal, therefore giving greater noise immunity.

Here we describe a differential driver that can be adapted to either a voltage or current output DAC. The driver is based on the dual AD8042 op amp configured as a cross-coupled differential driver. The AD8042 has a rail-to-rail output stage that operates within 30 mV of either rail and an input stage that can operate 200 mV below the negative supply (ground in this circuit) and within 1 V of the positive supply. In addition, the AD8042 has 160 MHz bandwidth and fast settling time, making it an ideal choice for the output driver.

The voltage output DAC is the 12-bit AD5620, a member of the nanoDAC^® family. The DAC contains an on-chip 5 ppm/°C reference and is available in an 8-lead SOT-23 or MSOP package. The current output DAC is the 12-bit AD5443, which is available in a 10-lead MSOP package.

The two circuits represent a cost effective, low power, and small board area solution for generating differential signals from industrial CMOS DACs. Both circuits operate on a single +5 V supply.

Data acquisition systems with wide dynamic range often need some method for adjusting the input signal level to the analog-to-digital converter (ADC). In order to get the most from an ADC, the maximum input signal should match its full-scale voltage. This is achieved by implementing a programmable gain amplifier circuit.

This circuit provides a programmable gain function using a quad SPST switch (ADG1611) and a resistor-programmable instrumen-tation amplifier (AD620).

The gain values are set by controlling the external gain setting resistor value, R_G, with the four SPST switches, which are connected to four precision resistors.

Low switch on resistance is critical in this application, and the ADG1611 has the industry’s lowest R_ON (1 Ω typical) and is available in the smallest package, a 16-lead, 4 mm × 4 mm LFCSP.

The combination of the industry-standard low cost AD620 and the ADG1611 quad switch yields unmatched performance in this circuit and provides all the benefits of a precision instrumentation amplifier, along with the programmable gain feature.

Achieving true 16-bit performance with a voltage output DAC requires selecting not only the correct DAC but also the correct complementary supporting components. This circuit provides a low risk solution for precision 16-bit digital-to-analog conversion using the AD5542A/AD5541A voltage output DAC with the ADR421 voltage reference and the AD8675 ultralow offset op amp used as the voltage reference buffer.

The reference buffer is critical to the design because the input impedance at the DAC reference input is heavily code- dependent and will lead to linearity errors if the DAC reference is not adequately buffered. With a high open-loop gain of 120 dB, the AD8675 has been proven and tested to meet the settling time, offset voltage, and low impedance drive capability required by this circuit application.

The precision, low offset OP1177 can be used as an optional output buffer if needed.

This combination of parts provides industry-leading 16-bit integral nonlinearity (INL) of ±1 LSB and differential nonlinearity (DNL) of ±1 LSB with guaranteed monotonicity, as well as low power, small PCB area, and cost effectiveness.