本文介紹了AD5421主要特性, 功能方框圖,和HART調制解調器連接框圖以及應用框圖.

ADI公司的AD5421是完整的16位4mA-20mA轉換器,包括用來給自身和發送器中其它器件供電的穩壓器,輸出電壓從1.8V到12V,漂移為5ppm/℃.器件還包括精密的1.25V和2.5V基準電壓源. AD5421采用標準的HART FSK協議通信,串口速率高達20Mbps,主要應用在工業過程控制,4-20mA回路供電發送器以及智能發送器.
16-Bit, Serial Input, Loop-Powered, 4mA to 20mA DAC

The AD5421 is a complete, loop powered, digital to 4mA-to-20mA converter, designed to meet the needs of smart transmitter manufacturers in the Industrial Control industry.It provides a high precision, fully integrated, low cost solution in a compact TSSOP package.

The AD5421 includes a regulated voltage output that is used to power itself and other devices in the transmitter. This regulator provides a regulated 1.8V to 12V output voltage. The device also contains precision 1.25V and 2.5V references, The AD5421 thus eliminates the need for a discrete regulator and voltage reference.

The AD5421 can be used with standard HART FSK protocol communication circuitry without any degradation in specified performance. The high speed serial interface is capable of operating at 20 Mbps and allows for simple connection to commonly-used microprocessors and microcontrollers via a SPI compatible three-wire interface.

The AD5421 is guaranteed monotonic to 16-bits, offers 0.0015% integral nonlinearity, 0.03% offset error and 0.03 % gain error.

The AD5421 is available in a 28 lead TSSOP package and is specified over the extended industrial temperature range of –40℃ to +105℃.

AD5421主要特性:

16-Bit Resolution and Monotonicity

Pin selectable NAMUR Compliant Ranges

4mA to 20mA

3.8mA to 21mA

3.2mA to 24mA

NAMUR Compliant ALARM Currents

Downscale ALARM current = 3.2mA

Upscale ALARM Current = 22.8mA/24mA

0.05% maximum Total Unadjusted Error (TUE)

0.0015% maximum INL Error (15 Bits minimum)

5ppm/℃ typ Output Drift

350uA maximum Quiescent Current

Flexible SPI Compatible Serial Digital Interface

Schmitt Triggered Inputs

On-Chip Fault Alerts via FAULT pin or ALARM Current

Loss of SPI Interface Control

SPI Communication Error (Packet Error Check)

Programmed Loop Current out of Range

Insufficient Loop Voltage

Over Temperature

Automatic Readback of Fault Register on each write cycle

Slew Rate Control Function

Gain and Offset Adjust Registers

On-Chip Reference (10 ppm/℃ Max)

Selectable Regulated Voltage Output

Loop Voltage Range

5.5V to 52V

Temperature Range: -40℃ to +105℃

TSSOP Package

HART Compatible

AD5421應用:

Industrial Process Control

4-20mA Loop Powered Transmitter

Smart Transmitter

圖1.AD5421功能方框圖

圖2.AD5421和HART調制解調器連接框圖

圖3.AD5421應用框圖