AD421 Loop-Powered 4-20 mA DAC

The AD421 includes a selectable regulator that is used to power itself and other devices in the transmitter. This regulator provides either a +5 V, +3.3 V or +3 V regulated output voltage. The part also contains +1.25 V and +2.5 V precision references. The AD421 thus eliminates the need for a discrete regulator and voltage reference. The only external components required are a number of passive components and a pass transistor to span large loop voltages. The AD421 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 10 Mbps and allows for simple connection to commonly-used microprocessors and microcontrollers via a standard three-wire serial interface. The sigma-delta architecture of the DAC guarantees 16-bit monotonicity while the integral nonlinearity for the AD421 is ±0.01%. The part provides a zero scale 4 mA output current with ±0.1% offset error and a 20 mA full-scale output current with ±0.2% gain error. The AD421 is available in a 16-pin, 0.3 inch-wide, plastic DIP and a 16-lead, 0.3 inch-wide, SOIC package. The part is specified over the industrial temperature range of -40°C to +85°C.

The AD421 is a complete, loop-powered, digital to 4-20 mA 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 16-pin package. The AD421 is ideal for extending the resolution of smart 4-20 mA transmitters at very low cost.

The AD421 includes a selectable regulator that is used to power itself and other devices in the transmitter. This regulator provides either a +5 V, +3.3 V or +3 V regulated output voltage. The part also contains +1.25 V and +2.5 V precision references. The AD421 thus eliminates the need for a discrete regulator and voltage reference. The only external components required are a number of passive components and a pass transistor to span large loop voltages.

The AD421 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 10 Mbps and allows for simple connection to commonly-used microprocessors and microcontrollers via a standard three-wire serial interface.

The sigma-delta architecture of the DAC guarantees 16-bit monotonicity while the integral nonlinearity for the AD421 is ±0.01%. The part provides a zero scale 4 mA output current with ±0.1% offset error and a 20 mA full-scale output current with ±0.2% gain error.

The AD421 is available in a 16-pin, 0.3 inch-wide, plastic DIP and a 16-lead, 0.3 inch-wide, SOIC package. The part is specified over the industrial temperature range of -40°C to +85°C.

Features and Benefits
  • 4mA to 20 mA Current Output
  • HART@ Compatible
  • 16-Bit Resolution and Monotonicity
  • ±0.01% Integral Nonlinearity
  • 5 V or 3 V Regulator Output
  • 2.5 V and 1.25 V Precision Reference
  • 750 µA Quiescent Current max
  • Programmable Alarm Current Capability
  • Flexible High Speed Serial Interface
  • 16-Lead SOIC and PDIP Packages
  • Interface & Isolation
    Digital to Analog Converters
    Data Sheets
    Documentnote
    AD421: Loop-Powered 4-20 mA DAC Data Sheet (Rev. C)PDF 171 kB
    Application Notes
    Documentnote
    AN-534: Adding HART® Capability to the AD421, Loop-Powered 4 mA–20 mA DAC Using the 20C15 HART Modem (Rev. B)PDF 49 kB
    Order Information
    Part NumberPackagePacking QtyTemp RangePrice 100-499Price 1000+RoHS
    AD421BN Last Time Buy16 ld PDIPOTH 25-40 to 85C11.079.39N
    AD421BNZ Production16 ld PDIPOTH 25-40 to 85C9.127.73Y
    AD421BR Last Time Buy16 ld SOIC - WideOTH 47-40 to 85C9.37.9N
    AD421BRRL7 Last Time Buy16 ld SOIC - WideREEL 400-40 to 85C07.9N
    AD421BRZ Production16 ld SOIC - WideOTH 47-40 to 85C8.056.83Y
    AD421BRZRL Production16 ld SOIC - WideREEL 1000-40 to 85C06.83Y
    AD421BRZRL7 Production16 ld SOIC - WideREEL 400-40 to 85C8.056.83Y
    Reference Materials
    AD421: Loop-Powered 4-20 mA DAC Data Sheet (Rev. C) ad421
    AD421:环路供电型4 mA-20 mA DAC 数据手册 (Rev. C) ad421
    AD421参考代码 ad421
    AN-534: Adding HART® Capability to the AD421, Loop-Powered 4 mA–20 mA DAC Using the 20C15 HART Modem (Rev. B) ad421
    AN-534: 采用20C15* HART调制解调器为路供电型4mA–20mA DAC AD421增添HART®性能 (Rev. A) ad421
    Digital to Analog Converters ICs Solutions Bulletin ad5590