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        The SD2421 is a complete 4-20mA loop powered DAC which converts digital signal into current. Its large scale integration, high precision, and low cost design is specifically well suited for smart 4-20mA transmitter manufacturer in the industrial control area.
        The DAC uses Σ-Δ architecture. It guarantees 16 bits resolution and monotonicity, and ±0.01% integral nonlinearity. The IC provides 4mA zero scale output current (±0.02% FS error), and 20mA full scale output current (±0.1% FS error). Full scale setup time to ±0.1% is less than 8ms.
        The SD2421 has a built-in voltage regulator that can be set to 3V, 3.3V, or 5V through different pin connections. The IC also has built-in 2.5V and 1.25V precision voltage references. Both regulator and precision references are used by the IC itself, and can also be used by other devices in the transmitter system. Thus, there is no need for standalone regulator or precision reference. However, a pass transistor is required in order to extend the loop operating voltage range. Together with this transistor, the SD2421 system can work from VCC+2V to the transistor’s breakdown voltage.
        The SD2421 can work together with HART or other similar FSK protocols without affecting the IC’s own performance. It communicates to microcontroller through three serial ports. The simple scheme can operate up to 3Mbps.
        The SD2421 has programmable alarm current function that can send out of range current to indicate malfunction. There is built-in short circuit protect between COM and LOOPRTN, and over current protection between BOOST and LOOPRTN.