The AD421 is a single chip, high performance, low cost solution for generating 4 mA to 20 mA signals for smart industrial control transmitters.
The AD421 is a single‑chip, loop‑powered 4 mA to 20 mA DAC designed for smart industrial transmitters. It integrates a 16‑bit sigma‑delta DAC, voltage regulator, and two precision reference outputs (+1.25 V and +2.5 V). The device can be powered from the loop voltage and provides selectable regulated outputs of 3 V, 3.3 V or 5 V.
The handbook includes functional block diagrams, detailed pin descriptions, timing characteristics for the high‑speed serial interface (up to 10 Mbps), electrical specifications, ordering information, and guidelines for external component selection such as the pass transistor and compensation capacitors.
| Resolution | 16 Bits |
|---|---|
| Integral Nonlinearity | ±0.01 % of FS |
| Full‑scale Settling Time | 8 ms typ |
| Quiescent Current @ VCC=3 V | 650 µA max |
| Regulated Output Voltage Options | 3 V, 3.3 V, 5 V |
The AD421 provides a normal output current range of 4 mA to 20 mA.
The device can tolerate up to 350 V loop voltage, limited by the breakdown voltage of the external pass transistor.
The high‑speed serial interface can operate up to 10 Mbps (10 MHz clock).