原标题：OnSemi A5191HRT-D HART调制解调器参考设计方案

　　OnSemi公司的A5191HRT-D是一款应用于现场仪表及控制的HART单芯片CMOS调制解调器芯片，该芯片具有通过外围器件少数被动器件就可以满足HART物理层的设计需要，可以实现调制、解调、接收滤波、载波监测和输出信号整形等功能。本芯片采用半双功通信模式，为节省电能，在发送信号时，接收电路部分关闭，反之亦然。本文首先介绍芯片的简介、特性、内部框图及应用领域，并给出相应设计方案的设计原理图、元器件列表及PCB元件布局图。

　　The A5191HRT is a single−chip, CMOS modem for use in highway addressable remote transducer (HART) field instruments and masters. The modem and a few external passive components provide all of the functions needed to satisfy HART physical layer requirements including modulation, demodulation, receive filtering, carrier detect, and transmit−signal shaping.

　　The A5191HRT uses phase continuous frequency shift keying (FSK) at 1200 bits per second. To conserve power the receive circuits are disabled during transmit operations and vice versa. This provides the half−duplex operation used in HART communications.

　　A5191HRT主要特性：

　　• Single−chip, Half−duplex 1200 Bits per Second FSK Modem

　　• Bell 202 Shift Frequencies of 1200 Hz and 2200 Hz

　　• 3.0 V − 5.5 V Power Supply

　　• Transmit−signal Wave Shaping

　　• Receive Band−pass Filter

　　• Low Power: Optimal for Intrinsically Safe Applications

　　• Compatible with 3.3 V or 5 V Microcontroller

　　• Internal Oscillator Requires 460.8 kHz Crystal or Ceramic Resonator

　　• Meets HART Physical Layer Requirements

　　• Industrial Temperature Range of −40°C to +85°C

　　• Available in 28−pin PLCC, 32−pin QFN and 32−pin LQFP Packages

　　• These are Pb−Free Devices

　　A5191HRT应用：

　　• HART Multiplexers

　　• HART Modem Interfaces

　　• 4 − 20 mA Loop Powered Transmitters

　　图1. A5191HRT内部方框图

　　A5191HRT方案介绍：

　　The A5191HRTNGEVB evaluation board includes all external components needed for operating the A5191HRT IC and demonstrates the small PCB surface area such an implementation requires. The EVB allows easy design of HART implementations using A5191HRT.

　　A5191HRT方案原理图：

　　图2. A5191HRT方案原理图

　　A5191HRT方案材料清单：

　　PCB元件布局图：