电路笔记 CN-0064 采用 AD5662 DAC

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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
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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).
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