电路笔记 CN-0064 连接/参考器件 利用 ADI 公司产品进行电路设计 放心运用这些配套产品迅速完成设计。 欲获得更多信息和技术支持,请拨打 4006-100-006 或 访问www.analog.com/zh/circuits 。 AD5662 16 位VOUT/IOUT DAC ADR02 5 V 精密基准电压源 AD822 36 V FET 精密双通道放大器 ADuM1401 四通道数字隔离器 采用 AD5662 DAC、ADuM1401 数字隔离器和外部放大器的 16 位全隔离 4 mA 至 20 mA 输出模块 电路功能与优势 本电路提供一种完整的工业控制输出模块解决方案。该设计 适合需要提供 4 mA至 20 mA电流输出范围的过程控制可编 程逻辑控制器(PLC)、分布式控制系统(DCS)模块和发射器。 AD5662 nanoDAC®是一款 5 V、16 位DAC,采用SOT-23 封 装。ADuM1401 四通道数字隔离器则提供微控制器与DAC之 间所需的全部信号隔离。本电路还含有标准外部保护功能, 且经过测试和验证,完全符合IEC 61000 标准。 过检测电阻 RS 的电流,因而也决定流过 R1 的电流。利用运 算放大器 AD822 的第二半节,该电流镜像(10×)到 R2。选择 AD822 放大器是因为其能以高性能、高电压工作。该电流镜 的第一级需要以 0 V 输入工作,确保当 DAC 以零电平输出工 作时无死区。这就要求 AD822 的负电源电压至少为−1 V,使 得 AD822 的第一级输出具有充足的裕量。第二级的两个二极 管与正电源 串联,用来 确保第二级 的输出电压 不会到达 AD822 的正供电轨,后者可以高达 35 V。FET 的输出同样受 电路描述 到一个串联二极管的保护。请注意,该串联二极管会增加电 对于工业控制模块, 模拟输出电流范围通常为 4 mA 至 20 mA 路的功耗,这在一些应用中可能会成为问题。 或 0 mA 至 20 mA。AD5662 提供 0 V 至 5 V 输出,可设置流 图 1. 16 位隔离式 4 mA至 20 mA工业控制输出模块(原理示意图) Rev.A “Circuits from the Lab” from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any “Circuit from the Lab”. (Continued on last page) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2009-2010 Analog Devices, Inc. All rights reserved. 电路笔记 CN-0064 ADR02 的温度漂移最大值为 9 ppm/°C。它的输入电压范围最 高达 36 V,因此也经常用于工业应用。 ADuM1401 是一款采用ADI公司iCoupler®技术的四通道数字 隔离器。它可用来在AD5662 与系统微控制器之间实现隔离, 隔离额定值为 2.5 kV(均方根值)。可以用三条线( SYNC 、 SCLK和DIN),将标准SPI接口与AD5662 相连。 图 2所示为AD5662 采用外部基准电压源ADR02 时,电路输 出到RL中的电流输出误差曲线(积分非线性)。结果显示了 %FSR(满量程范围)与输入码的函数关系。本电路选择 ADR02 为基准电压源。 图 2. INL 精度曲线(24 mA 满量程输出范围) 本设计还含有外部保护功能(如标准保护二极管和TVS器件 等),且成功通过测试,符合IEC 61000标准,如表 1所示。 关于外部保护技术的详细讨论,请参考Colm Slattery、Derrick Hartmann和Li Ke合作撰写的“PLC评估板简化工业过程控制 系统设计”一文(《模拟对话》,43-04,2009 年 4 月)。 表 1. 符合 IEC 标准 测试项目 描述 结果 静电放电(ESD),±4 kV VCD 最大偏差:0.32%(CH3. Class B) 静电放电(ESD),±8 kV HCD 最大偏差:0.28%(CH3. Class B) 辐射抗扰度 80 MHz 至 1 GHz(10 V/m) ,垂直天线极化 最大偏差:0.09%(CH1),0.30%(CH3. Class B) 辐射抗扰度 80 MHz 至 1 GHz(10 V/m) ,水平天线极化 最大偏差:–0.04%(CH1),0.22%(CH3. Class B) 辐射抗扰度 1.4 GHz 至 2 GHz(3 V/m),垂直天线极化 最大偏差:0.01%(CH1),-0.09%(CH3. Class B) 辐射抗扰度 1.4 GHz 至 2 GHz(3 V/m),水平天线极化 最大偏差:0.01%(CH1),0.09%(CH3. Class B) 电快速瞬变(EFT) ±2 kV 电源端口 最大偏差:–0.12%(CH3. Class B) 电快速瞬变(EFT) ±1 kV 信号端口 最大偏差:–0.02%(CH3. Class A) EN & IEC 61000-4-5 电源线突波,±0.5 kV 未发生电路板或器件损坏情况,符合 Class B 要求 EN & IEC 61000-4-6 对电源线执行抗扰度测试,10 V/m、5 分钟 最大偏差:0.09%(CH3. Class B) 对 I/O 电缆执行抗扰度测试,10 V/m、5 分钟 最大偏差:–0.93%(CH3. Class B) 磁场抗扰度,水平天线极化 最大偏差:–0.01%(CH3. Class A) 磁场抗扰度,垂直天线极化 最大偏差:–0.02%(CH3. Class A) EN & IEC 61000-4-2 EN & IEC 61000-4-3 EN & IEC 61000-4-4 EN & IEC 61000-4-8 Rev. A | Page 2 of 3 电路笔记 CN-0064 进一步阅读 数据手册和评估板 ® Chen, Baoxing. 2006. iCoupler Products with isoPower™ AD5662 Data Sheet. Technology: Signal and Power Transfer Across Isolation Barrier AD822 Data Sheet. Using Microtransformers. Analog Devices. ADR02 Data Sheet. Slattery, Colm, Derrick Hartmann, and Li Ke. “PLC Evaluation ADuM1401 Data Sheet. Board Simplifies Design of Industrial Process Control Systems.” ADuM1401Evaluation Board. Analog Dialogue (April 2009). OP2177 Data Sheet. MT-014 Tutorial, Basic DAC Architectures I: String DACs and PLC Demo System. Thermometer (Fully Decoded) DACs, Analog Devices. MT-015 Tutorial, Basic DAC Architectures II: Binary DACs, 修订历史 Analog Devices. 1/10—Rev. 0 to Rev. A MT-016 Tutorial, Basic DAC Architectures III: Segmented DACs, Analog Devices. Wayne, Scott. “iCoupler® Digital Isolators Protect RS-232, Change to Figure 1 ........................................................................... 1 7/09—Revision 0: Initial Version RS-485, and CAN Buses in Industrial, Instrumentation, and Computer Applications.” Analog Dialogue (October 2005). (Continued from first page) "Circuits from the Lab" are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the "Circuits from the Lab" in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the "Circuits from the Lab". Information furnished by Analog Devices is believed to be accurate and reliable. However, "Circuits from the Lab" are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any "Circuits from the Lab" at any time without notice, but is under no obligation to do so. Trademarks and registered trademarks are the property of their respective owners. ©2009–2010 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN08346sc-0-1/10(A) w w w . a n a l o g . c o m Rev. A | Page 3 of 3