ОБЩЕЕ ОПИСАНИЕ

The AD5410 are low cost, precision, fully integrated 12-/16-bit converters offering a programmable current source output designed to meet the requirements of industrial process control applications. The output current range is programmable at 4 mA to 20 mA, 0 mA to 20 mA, or an overrange function of 0 mA to 24 mA. The output is open-circuit protected. The device operates with a power supply (AVDD) range from 10.8 V to 60 V. Output loop compliance is 0 V to AVDD − 2.5 V.The flexible serial interface is SPI, MICROWIRE™, QSPI™, and DSP compatible and can be operated in 3-wire mode to minimize the digital isolation required in isolated applications. The device also includes a power-on reset function, ensuring that the device powers up in a known state, and an asynchronous CLEAR pin that sets the output to the low end of the selected current range.The total unadjusted error is typically ±0.01% FSR.

DIGITAL POWER SUPPLY

By default, the DVCC pin accepts a power supply of 2.7 V to 5.5V. Alternatively, via the DVCC SELECT pin, an internal 4.5 V power supply can be output on the DVCC pin for use as a digital power supply for other devices in the system or as a termination for pull-up resistors. This facility offers the advantage of not having to bring a digital supply across an isolation barrier. The internal power supply is enabled by leaving the DVCC SELECT pin unconnected.To disable the internal supply, DVCC SELECT should be tied to 0 V.DVCC is capable of supplying up to 5 mA of current.

LAYOUT GUIDELINES

In any circuit where accuracy is important, careful consideration of the power supply and ground return layout helps to ensure the rated performance. The printed circuit board (PCB) on which the AD5410 are mounted should be designed so that the analog and digital sections are separated and confined to certain areas of the board. If the AD5410 are in a system where multiple devices require an AGND-to-DGND connection, the connection should be made at one point only. The star ground point should be established as close as possible to the device.The AD5410 should have ample supply bypassing of 10µF in parallel with 0.1 µF on each supply, located as close to the package as possible, ideally right up against the device. The 10µF capacitors are the tantalum bead type. The 0.1 µF capacitorshould have low effective series resistance (ESR) and low effective series inductance (ESI), such as the common ceramic types, which provide a low impedance path to ground at high frequencies to handle transient currents due to internal logic switching.The power supply lines of the AD5410/AD5420 should use as large a trace as possible to provide low impedance paths and to reduce the effects of glitches on the power supply line. Fast-switching signals such as clocks should be shielded with digital ground to avoid radiating noise to other parts of the board and should never be run near the reference inputs. A ground line routed between the SDIN and SCLK lines helps reduce crosstalk between them (notrequired on a multilayer board that has a separate ground plane,but separating the lines helps). It is essential to minimize noise on the REFIN line because noise can couple through to the DAC output.Avoid crossover of digital and analog signals. Traces on opposite sides of the board should run at right angles to each other. This reduces the effects of feedthrough on the board. A microstrip technique is by far the best method but is not always possible with a double-sided board. In this technique, the component side of the board is dedicated to the ground plane, and signal traces are placed on the solder side.