High-voltage SAR ADCs boost system accuracy in industrial applications

October 09, 2014 // By Graham Prophet
Texas Instruments has added successive-approximation register (SAR) analogue-to-digital converters that are the first in a new high-voltage family, fully integrated devices with single 5-V supply to simplify high-voltage designs.

The eight-channel ADS8688 and four-channel ADS8684 allow input ranges up to ±10.24 V to be powered by a single 5-V supply, simplifying system power requirements. They claim the industry's lowest gain drift, offset voltage and offset drift, and the highest precision reference, increasing levels of accuracy throughout the full extended industrial temperature range.

These ADCs can improve total system accuracy in a broad range of multi-channel industrial applications, including power automation, low- and medium-voltage relay protection, protection relay monitoring, factory automation equipment and programmable logic controllers (PLCs).

The ADS8688 family does not need high-voltage supplies; they support bipolar input ranges up to ±10.24 V and unipolar ranges up to ±10.24 V with a single 5-V supply. DC error performance: the parts achieve better than 99.9% accuracy without calibration with DC error specifications that boost system-level performance. With specified gain drift of 4 ppm/C and offset drift of 3 ppm/C, the devices eliminate the need for designers to spend time calibrating their systems over temperature ranges. An integrated precision reference and reference buffer improve low-temperature drift specifications, enabling precision performance without requiring external circuitry across the full extended industrial temperature range of minus 40C to 125C.

Each device integrates into one chip 20 active devices, including programmable gain amplifiers (PGAs), driver amplifiers, multiplexer, voltage reference, reference buffer and SAR ADC, plus an auxiliary channel input for interfacing straight to the ADC. This integration allows the ADS8688 and ADS8684 to connect directly to various sensor types that require no signal conditioning.

Tools and support include simulation models, hardware evaluation kits and reference designs: designers can evaluate the ADS8688 and ADS8684 in a fraction of the time they might spend, TI says, in evaluating other precision ADCs by using a new performance demonstration kit (PDK) that features a simple installation process. The PDK includes an evaluation module (EVM) and capture card for plug-and-play functionality, replacing online software installations with a one-click process. The