4-20mA DAC has internal DC/DC to operate from a single rail

March 10, 2017 // By Graham Prophet
Texas Instruments’ DAC8775 is a precision data converter that saves board space for industrial automation designs. The16-bit digital-to-analogue converter (DAC) offers simpler power-supply design, and operates from a single, wide 12- to 36-V power rail using an integrated buck/boost converter to generate all of the required internal power supplies.

The four-channel DAC8775 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% smaller than the nearest competing device. This integrated DAC, TI says, can deliver smaller and more efficient designs with advanced diagnostic capabilities.


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 has an 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% 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 DAC8775’s high DC performance reduces the need for system calibration, saving manufacturing costs compared to a discrete solution. The DAC8775 dynamically adjusts the generated supply based on the current load on the 4-20mA loop. This 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 high-efficiency synchronous buck converter that dissipates less than 1W in factory-automation implementations. An evaluation module is available for $149 for designers to simulate and optimize the DAC8775. The part itself comes in a 10 x 10-mm quad-flat no-lead (QFN) package and is priced at $15.72 (1,000).


TI; www.ti.com/DAC8775-pr-eu