The AD421 is a complete loop-powered, digital 4-20 mA
converter, designed to meet the needs of smart transmitter manufacturers in the industrial control field. 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 transmitters from 4 to 20 mA at a very low cost.
The AD421 contains an optional regulator to power itself and other components in the transmitter. This regulator provides regulated output voltages of +5 V, +3.3 V, or +3 V. The device also includes precision +1.25 V and +2.5 V references. Therefore, the AD421 does not require a discrete regulator and reference. External components require only a few passive components and a pass transistor to extend the large loop voltage range.
The AD421 can be used with standard HART FSK protocol communication circuitry without compromising performance. The high-speed serial interface operates at 10 Mbps and allows simple interfacing to popular microprocessors and microcontrollers via a standard 3-wire serial interface.
The DAC uses a sigma-delta architecture that guarantees 16-bit monotonicity with an integral nonlinearity of ±0.01%. The device provides 4 mA of zero-scale output current with ±0.1% offset error) and 20 mA full-scale output current with ±0.2% gain error.
The AD421 is available in a 16-lead, 0.3-inch-wide, plastic DIP package and a 16-lead, 0.3-inch-wide, SOIC package. It is specified over the industrial temperature range of -40°C to +85°C.