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Voltage references flaunt Kelvin sensing

Dallas — Capable of both sourcing and sinking current, Texas Instruments Inc.'s 4 ppm/°C temperature drift voltage reference family from the company's Burr-Brown product line boasts high accuracy.

The micro-size SOT23-6 packaging and micro power consumption make this product family suited for portable and battery-operated applications, medical and test equipment, as well as data acquisition systems.

The REF32xx family features high-output current of ±10 mA and is stable with any capacitive load. To increase precision, the REF32xx uses force and sense pins that allow four-wire Kelvin connection measurement to effectively eliminate the impact of contact and trace resistance.

Other features include low quiescent current of 100 μA, with a maximum quiescent current over temperature of only 135 μA. Typically, the quiescent current changes less than 2 μA over the entire supply range.

The REF32xx can be operated from as low as 5 mV above the desired output voltage under no-load conditions. When shut down, supply current is reduced to less than 1 μA.

All models in this product family are specified for the wide industrial temperature range of -40°C to 125°C and offer low temperature drift (see related chart below ).

 
 
See related temperature chart

The REF32xx is available now in the SOT23-6 package. The device costs $1.70 in 1,000- piece quantities. Click here for the REF32xx data sheet.

Texas Instruments , 1-800-477-8924, www.TI.com.

 
 
See related block diagram

This new family consists of six devices in different voltages (1.25 V up to 4.096 V). Prior to TI's acquisition of Burr-Brown four years ago, voltage reference ICs weren't a main focus for either Burr-Brown or TI, said Bruce Trump, strategic development manager for Burr-Brown's linear product group. Today, however, the combined companies have become a viable player in this arena, he said.

Some other precision voltage reference vendors include Analog Devices Inc., Intersil Corp., Linear Technology Corp., and Maxim Integrated Products Inc. Check out a similar device that was recently released by Intersil (Milpitas, Calif.).Click here to see Intersil’s ILS600007 .

What makes Burr-Brown's products special is their high level of accuracy — particularly the drift of the products at low quiescent current (100 μA), Trump said. Often, there is a tradeoff with accuracy at a given quiescent current, he said. “Competing products with this low drift require higher quiescent current — about 50 percent higher,” Trump said.

Burr-Brown's earlier-generation voltage reference devices, dubbed the REF31 family, offered similar parts in different voltages. The latest family, however, touts improved voltage drift over temperature, Trump said. The older family is rated a little bit differently, but it's roughly half the drift of the previous family, Trump said. “We achieved this low drift via electronic trimming,” he said.

The company measures the devices at two difference temperatures — room temperature and high temperature. “The intent here is to measure the voltage references at two relatively widely spaced temperatures. Then, the devices can be adjusted to get the same voltage at both temperatures. Essentially, it removes the dominate temperature variation, leaving only a small residual curvature throughout the temperature range,” Trump said.

There are other similar devices out there with slightly different specs. In addition to the low drift over temperature aspect, the primary difference between these devices and other voltage reference ICs is that Burr-Brown's devices also feature Kelvin sensing, Trump said. “Kelvin sensing accounts for voltage drops in the ground and output terminals by acquiring the output amplifier's feedback directly across the high and low side of the load,” he explained.

Furthermore, Burr-Brown's ICs are capable of sourcing and sinking. Many other devices out there don't sink current even though applications frequently require excellent accuracy both when sourcing and sinking output current, Trump said. Consequently, sometimes designers will use an external resistor to load the output — this allows the combination of the resistor and the reference to effectively sink current. “This burns additional supply current though,” Trump added.

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