4-20mA DAC with integrated buck/boost converter operates from a single-supply

March 09, 2017 // By Nick Flaherty
The DAC8775 integrates a buck/boost converter to generate all of the required internal power supplies
Texas Instruments (TI) has developed a digital-to-analogue converter (DAC) that combines industry-leading precision performance with a simpler power-supply design.

The four channel 16-bit DAC8775 operates from a single, wide 12- to 36-V power rail by integrating a buck/boost converter to generate all of the required internal power supplies to save designers time, cost and significant board space.

The device addresses the trend in factory automation and process control equipment toward input/output (I/O) modules that must squeeze more channels into a smaller space. By combining a 4-20mA current and voltage driver with a precision reference and a buck/boost converter, the DAC8775 enables a total system footprint that is up to 25 percent smaller than the nearest competing device.

The DAC8775’s on-chip diagnostic features include smart alarms that monitor open load, short circuit, over-temperature, cyclic redundancy check (CRC), watchdog timer and compliance voltage. Designers can choose preset actions that help detect faults early to facilitate reliable system operation.

The device also has an innovative auto-learn feature that calculates the load impedance on the 4-20mA loop and clamps the power supply. This enables faster settling time, balancing efficiency with quicker system response. A total unadjusted error of 0.1 percent full-scale range (FSR) over an extended industrial temperature range of -40°C to 125°C enables designers to rate their output modules for higher temperature ranges. The DC performance also reduces the need for system calibration, saving manufacturing costs compared to a discrete solution.

Dynamically adjusting the generated supply based on the current load on the 4-20mA loop creates an efficient system with well-controlled thermal performance, allowing more channels in a smaller space.

A four-channel analogue output module reference design demonstrates the combination of the DAC8775 and the LM5166 that dissipates less than 1 W of power in factory-automation implementations. An evaluation module is available for US$149 for designers to simulate and optimize the DAC8775.

The DAC8775 is available in a 10-mm-by-10-mm quad-flat no-lead (QFN) package and is priced at US$15.72 in 1,000-unit quantities.