Loop-Powered a 4 mA to 20 mA DAC AD421 FEATURES FUNCTIONAL BLOCK DIAGRAM 4 mA to 20 mA Current Output HART Compatible REF IN REF OUT1 REF OUT2 16-Bit Resolution and Monotonicity LV (+2.5V) (+1.25V) (+2.5V) V CC 0.01% Integral Nonlinearity 75k 5 V or 3 V Regulator Output 112.5k 2.5 V and 1.25 V Precision Reference AD421 134k 750 A Quiescent Current max Programmable Alarm Current Capability DRIVE BANDGAP REFERENCE Flexible High Speed Serial Interface COMP 121k 16-Lead SOIC and PDIP Packages BOOST LOCAL OSCILLATOR DATA INPUT SHIFT REGISTER CLOCK SWITCHED 16-BIT CURRENT DAC LATCH SIGMA- SOURCES LATCH 40 DELTA DAC AND GENERAL DESCRIPTION FILTERING 80k LOOP POWER-ON The AD421 is a complete, loop-powered, digital to 4 mA to RTN RESET 20 mA converter, designed to meet the needs of smart trans- mitter manufacturers in the Industrial Control industry. It pro- COM C1 C2 C3 vides a high precision, fully integrated, low cost solution in a compact 16-lead package. The AD421 is ideal for extending the PRODUCT HIGHLIGHTS resolution of smart 4 mA to 20 mA transmitters at very low cost. 1. The AD421 is a single chip, high performance, low cost The AD421 includes a selectable regulator that is used to power solution for generating 4 mA to 20 mA signals for smart itself and other devices in the transmitter. This regulator pro- industrial control transmitters. vides either a +5 V, +3.3 V or +3 V regulated output voltage. 2. The AD421s regulated supply voltage can be used to power The part also contains +1.25 V and +2.5 V precision references. any additional circuits in the transmitter. The regulated The AD421 thus eliminates the need for a discrete regulator output value is pin selectable as either +3 V, +3.3 V or +5 V. and voltage reference. The only external components required are a number of passive components and a pass transistor to 3. The AD421s on-chip references can provide a precision span large loop voltages. reference voltage to other devices in the system. This refer- ence voltage can be either +1.25 V or +2.5 V. The AD421 can be used with standard HART FSK protocol communication circuitry without any degradation in specified 4. The AD421 is fully compatible with standard HART cir- performance. The high speed serial interface is capable of oper- cuitry or other similar FSK protocols. ating at 10 Mbps and allows for simple connection to com- 5. With the addition of a single discrete transistor, the AD421 monly-used microprocessors and microcontrollers via a standard can be operated from V + 2 V min to a maximum of the CC three-wire serial interface. breakdown voltage of the pass transistor. The sigma-delta architecture of the DAC guarantees 16-bit 6. The AD421 converts the digital data to current with 16-bit monotonicity while the integral nonlinearity for the AD421 is resolution and monotonicity. Full-scale settling time to 0.01%. The part provides a zero scale 4 mA output current 0.1% typically occurs within 8 ms. with 0.1% offset error and a 20 mA full-scale output current 7. The AD421 features a programmable alarm current capabil- with 0.2% gain error. ity that allows the transmitter to send out of range currents to The AD421 is available in a 16-lead, 0.3 inch-wide, plastic DIP indicate a transducer fault. and in a 16-lead, 0.3 inch-wide, SOIC package. The part is speci- fied over the industrial temperature range of 40C to +85C. HART is a registered trademark of the HART Communication Foundation. REV. C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. use, nor for any infringements of patents or other rights of third parties Tel: 781/329-4700 World Wide Web Site: AD421* PRODUCT PAGE QUICK LINKS Last Content Update: 02/23/2017 COMPARABLE PARTS DESIGN RESOURCES View a parametric search of comparable parts. AD421 Material Declaration PCN-PDN Information DOCUMENTATION Quality And Reliability Application Notes Symbols and Footprints AN-534: Adding HART Capability to the AD421, Loop- Powered 4 mA20 mA DAC Using the 20C15 HART DISCUSSIONS Modem View all AD421 EngineerZone Discussions. Data Sheet AD421: Loop-Powered 4-20 mA DAC Data Sheet SAMPLE AND BUY Visit the product page to see pricing options. REFERENCE MATERIALS Solutions Bulletins & Brochures TECHNICAL SUPPORT Digital to Analog Converters ICs Solutions Bulletin Submit a technical question or find your regional support number. DOCUMENT FEEDBACK Submit feedback for this data sheet. This page is dynamically generated by Analog Devices, Inc., and inserted into this data sheet. A dynamic change to the content on this page will not trigger a change to either the revision number or the content of the product data sheet. This dynamic page may be frequently modified.