Precision voltage references form the basis for numerous measurement, data acquisition, and control circuits: the meter stick to which a data converter can play vernier. But as is the case with the data converters, voltage references are parametric circuits in their own right.

After their initial accuracy, the next most critical performance characteristic for a reference is usually its voltage temperature coefficient. Except for the rare application that operates over a narrowly controlled temperature range, ambient temperature variations degrade the accuracy of the reference’s output voltage.

Many modern electronic systems add two constraints that complicate reference performance: Most obvious from the outside, many applications that have historically operated from mains power have evolved into the realm of portable equipment. As a result, these system designs must minimize quiescent current to avoid hurrying their energy sources toward the end-of-charge-cycle portion of battery discharge curves.

Second, with the voltage scaling that has necessarily accompanied IC-fabrication-process shrinks, the handiest analog voltage rail from which to power the reference may be one whose lower limit is scantly greater than the reference’s output. So, even in applications that remain powered by robust and reliable energy sources, the reference’s dropout voltage may rise on the list of designers’ concerns.

With these constraints in mind, I couldn’t help but notice Linear Technology’s recent announcement of its LT6656 precision voltage reference. The IC is available in two grades: An A-grade device yields a maximum initial output-voltage error of 0.05% and a maximum temperature coefficient of 10 ppm/°C. A B-grade device delivers a 0.1% maximum initial output voltage error and a 20- ppm/°C maximum tempco.

The standard versions of the LT6656 produces a 2.5 V output. Contact the supplier if you require any of the optional output voltages: 1.25 V, 2.048 V, 3.0 V, 3.3 V, 4.096 V, or 5.0 V.

The ‘6656 is also available for two temperature ranges—0 °C to 70 °C and -40 °C to 85 °C. The references remain operational over a -55 °C to 125 °C temperature range. Linear Technology specifies the 2.5 V reference with a 3 V input, but the device can operate on supplies as large as 18 V. The maximum quiescent current is 1 μA (850 nA, typical), rising to a maximum 1.5 μA over temperature.

Delivering its 5-mA full rated load current over the specified temperature range, the ‘6656’s maximum dropout voltage is 500 mV. At lower currents, the maximum dropout voltage over temperature is smaller, falling to 40 mA at zero output current. At room temperature, the zero-current dropout voltage is an impressively small 10 mV.

The datasheet is available online. The LT6656 is available in TSOT-23-6 packages with pricing starting at $1.74 (1000).