The AD420 is a complete digital current loop output converter designed to meet the needs of the industrial control market. It provides a high-precision, fully integrated, low-cost single-chip solution for generating current loop signals in a compact 24-pin SOIC or PDIP package.
The output current range can be programmed to be 4 mA-20 mA, 0 mA-20 mA, or 0 mA-24 mA overrange. Alternatively, the AD420 can provide a voltage output from a separate pin, which needs to be configured with an external single buffer amplifier for 0 V-5 V, 0 V-10 V, ±5 V, or ±10 V outputs.
The 3.3 M baud serial input logic design minimizes galvanic isolation costs and enables simple interfacing with popular microprocessors. It can be used in 3-wire mode or asynchronous mode and provides a serial output pin to daisy-chain multiple DACs on one side of the isolated barrier current loop.
The AD420 uses Σ-DELTA (SD) DAC technology to achieve 16-bit monotonicity at a very low cost. Settling time of 0.1% of full scale does not exceed 3 ms. The external components require only three low-cost capacitors (except for standard transient protection circuitry) for use in the DAC output filter.
If the AD420 is to be used at extreme temperatures and supply voltages, an external output transistor can be used to minimize power dissipation on the chip via the "BOOST" pin.
When there is an open circuit in the loop, the FAULT DETECT pin generates a signal. An on-chip reference can be used to supply precision +5 V to external components outside the AD420; If the user requires temperature stability above 25 ppm/°C, an external precision reference such as the AD586 can also be used as the reference.
The AD420 is available in 24-lead SOIC and PDIP packages and operates over the industrial temperature range of -40°C to +85°C.
The AD420 data sheet (Rev F, 10/99) is available now with some new application information.