NS公司的DAC161P997是用来发送工业标准4-20mA电流回路的模拟输出电流的16位Sigma-Delta数模转换器(DAC),提供16位精度,低温度系数(29ppm/°C)的输出电流以及极好的长期输出电流漂移(90 ppmFS)性能,而功耗低于190uA,主要用于两线4-20mA电流回路发送器,工业过程控制,激烈器控制,工厂自动化,建筑物自动化,精密仪表,数据采集系统和测试系统.本文介绍了DAC161P997主要特性, 方框图,多种应用框图以及应用案例电路图,DAC161P997EVAL评估板电路图和元件布局图.

Single-Wire 16-bit DAC for 4-20mA Loops

The DAC161P997 is a 16- bit ΣΔ digital-to-analog converter (DAC) for transmitting an analog output current over an industry standard 4-20 mA current loop. It offers 16-bit accuracy with a low output current temperature coefficient (29ppm/°C) and excellent long-term output current drift (90 ppmFS) while consuming less than 190μA.

The data link to the DAC161P997 is a Single Wire Interface (SWIF) which allows sensor data to be transferred in digital format over an isolation boundary using a single isolation component. The DAC161P997’s digital input is compatible with standard isolation transformers and optocouplers. Error detection and handshaking features within the SWIF protocol ensure error free communication across the isolation boundary.

For applications where isolation is not required, the DAC161P997 interfaces directly to a microcontroller.

The loop drive of the DAC161P997 interfaces to a HART (Highway Addressable Remote Transducer) modulator, allowing injection of FSK modulated digital data into the 4-20mA current loop. This combination of specifications and features makes the DAC161P997 ideal for 2- and 4-wire industrial transmitters.

The DAC161P997 is available in a 16–lead LLP package and is specified over the extended industrial temperature range of -40°C to 105°C.

DAC161P997主要特性:

■ 16-bit linearity

■ Single-Wire Interface (SWIF), with handshake

■ Digital Data transmission (no loss of fidelity)

■ Pin Programmable Power-Up Condition

■ Self adjusting to input data rate

■ Loop error detection and reporting

■ Programmable output current error level

■ No external precision components

■ Simple interface to HART modulator

■ Small package: LLP-16 (4x4 mm, 0.5 mm pitch) 4.0 Key Specifications

■ Output Current TempCo 29 ppmFS/°C(max)

■ Long-Term Output Current Drift 90 ppmFS(typ)

■ INL +3.3/−2.1 μA(max)

■ Total Supply Current 190 μA(max)

DAC161P997应用:

• Two-wire, 4-20 mA current loop transmitter

• Industrial Process Control

• Actuator control

• Factory Automation

• Building Automation

• Precision Instruments

• Data Acquisition Systems

• Test Systems

图1. DAC161P997方框图

图2. DAC161P997工业用4-20mA发送器框图

图3. DAC161P997回路供电的发送器框图

图4. DAC161P997自供电的发送器框图

图5. 变压器耦合SWIF链接的DAC161P997发送器框图

图5. DAC161P997典型的SWIF链接框图

图6. 无双向I/O的主链接框图

图7.采用光耦的SWIF链接框图

图8. DAC161P997应用案例电路图

DAC161P997EVAL评估板

DAC161P997EVAL is the evaluation board for the DAC161P997 Single-Wire 16-bit DAC for 4-20mA Loops. This board will help the user evaluate the functionality and performance of the DAC161P997. It is also a demonstration tool for the DAC’s unique single wire interface (SWIF).

DAC161P997EVAL combined with SPIO4 Sensor AFE Digital Controller Board the user can easily build a 4-20mA remote industrial transmitter where the PC host emulates a process sensor.

图9.DAC161P997EVAL评估板外形图

图10.DAC161P997EVAL完整的评估系统

图11.DAC161P997EVAL评估板电路图

图12.DAC161P997EVAL评估板元件布局图
详情请见:
http://www.national.com/ds/DA/DAC161P997.pdf
和
http://www.national.com/assets/en/boards/DAC161P997_UserGuide.pdf