OnSemi公司的A5191HRT-D是一款應用于現場儀表及控制的HART單芯片CMOS調制解調器芯片，該芯片具有通過外圍器件少數被動器件就可以滿足HART物理層的設計需要，可以實現調制、解調、接收濾波、載波監測和輸出信號整形等功能。本芯片采用半雙功通信模式，為節省電能，在發送信號時，接收電路部分關閉，反之亦然。本文首先介紹芯片的簡介、特性、內部框圖及應用領域，并給出相應設計方案的設計原理圖、元器件列表及PCB元件布局圖。
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應用：
• HART Multiplexers
• HART Modem Interfaces
• 4 − 20 mA Loop Powered Transmitters
圖1. A5191HRT內部方框圖
A5191HRT方案介紹：
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方案原理圖：
圖2. A5191HRT方案原理圖
A5191HRT方案材料清單：
PCB元件布局圖：
