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AD421:  Loop-Powered 4-20 mA DAC

Product Details

Newer Alternatives:
  • AD5421: 16-Bit, Serial Input, Loop-Powered, 4mA to 20mA DAC

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.


  • Chinese data sheet available
  • 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

Functional Block Diagram for AD421

AD421 Diagram
Functional Block Diagram for AD421

Evaluation Kits & Symbols & Footprints

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Price, packaging, availability

AD421 Model Options
Model Package Pins Temp.
Price*(100-499) Price*1000 pcs RoHS View PCN/ PDN Check Inventory/
AD421BN Status: Production 16 ld PDIP 16 Ind Tube, 25 $10.06 $8.54 N  Material Info PCN Purchase
AD421BNZ Status: Production 16 ld PDIP 16 Ind Tube, 25 $8.29 $7.03 Y  Material Info PCN Purchase
AD421BR Status: Production 16 ld SOIC - Wide 16 Ind Tube, 47 $9.30 $7.90 N  Material Info PCN Purchase Sample
AD421BRRL7 Status: Production 16 ld SOIC - Wide 16 Ind Reel, 400 - $7.90 N  Material Info PCN Purchase
AD421BRZ Status: Production 16 ld SOIC - Wide 16 Ind Tube, 47 $8.05 $6.83 Y  Material Info PCN Purchase
AD421BRZRL Status: Production 16 ld SOIC - Wide 16 Ind Reel, 1000 - $6.83 Y  Material Info PCN Purchase
AD421BRZRL7 Status: Production 16 ld SOIC - Wide 16 Ind Reel, 400 $8.05 $6.83 Y  Material Info PCN Purchase
Price Table Help

The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.

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