Loop-Powered 4-20 mA 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.
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At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Solutions Bulletins & Brochures
Digital to Analog Converters ICs Solutions Bulletin
Build a Smart Analog Process-Instrument Transmitter with Low-Power...
(Analog Dialogue, Vol. 31, No. 1, 1997)
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
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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.