AD421

a FEATURES 4 mA 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 ␮A Quiescent Current max Programmable Alarm Current Capability Flexible High Speed Serial Interface 16-Lead SOIC and PDIP Packages DATA CLOCK LATCH REF IN (+2.5V) Loop-Powered 4 mA to 20 mA DAC AD421 FUNCTIONAL BLOCK DIAGRAM REF OUT1 REF OUT2 (+2.5V) (+1.25V) LV VCC 75k⍀ 112.5k⍀ AD421 BANDGAP REFERENCE 134k⍀ DRIVE 121k⍀ COMP BOOST LOCAL OSCILLATOR INPUT SHIFT REGISTER DAC LATCH 16-BIT SIGMADELTA DAC SWITCHED CURRENT SOURCES AND FILTERING GENERAL DESCRIPTION 40⍀ 80k⍀ LOOP RTN The AD421 is a complete, loop-powered, digital to 4 mA to 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-lead package. The AD421 is ideal for extending the resolution of smart 4 mA to 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 v...