4-20mA DAC integrates buck/boost converter

Article By : Texas Instruments

The DAC8775 adjusts the generated supply based on the current load on the 4mA-20mA loop, creating a system with well-controlled thermal performance.

Texas Instruments' 16bit DAC operates from a single, wide 12V to 36V power rail, leveraging an integrated buck/boost converter to generate all of the required internal power supplies to save designers time, cost and significant board space.

The four-channel DAC8775 addresses the trend in factory automation and process control equipment towards input/output (I/O) modules that must squeeze more channels into a smaller space. Engineers designing these systems face the challenge of managing power dissipation in a small form factor, according to the company.

By combining a 4mA-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 others, TI said.

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 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.

It also offers a total unadjusted error of 0.1% full-scale range (FSR) over an extended industrial temperature range of -40°C to 125°C, allowing 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.

__Figure 1:__ *DAC8775 block diagram (Source: TI)*

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, according to the company.

A four-channel analog output module reference design demonstrates the combination of the DAC8775 and the LM5166 high-efficiency synchronous buck converter that dissipates less than 1W of power in factory-automation implementations.

The DAC8775 is available now through the TI store and authorized distributors. The device comes in a 10mm x 10mm quad-flat no-lead (QFN) package and is priced at ₹1,068.88 ($15.72) in 1,000-unit quantities. An evaluation module is also available for ₹10,131.23 ($149) for designers to simulate and optimise the DAC8775.