16Bit Octal DAC suits open-loop and closed-loop systems

Linear Technology Corp. has introduced the LTC2656, a 16bit octal digital-to-analog converter (DAC) with 4LSB INL maximum over temperature – a significant performance gain over its LTC2600 16bit octal DAC, which offers 64LSB INL. The company claims that the LTC2656's INL value is three times that of its nearest octal competitor.

Though integral nonlinearity (INL) is not a critical parameter for DACs used in closed loop systems (because the ADC and digital algorithm can correct for the error), in an open loop system, DAC INL and differential nonlinearity (DNL) need to be as linear as possible (the system is not self-correcting). Thus, the combination of multiple DACs in a single package, all with good INL, makes the LTC2600 suitable for multichannel open loop and closed loop systems alike. Linear suggests that with its 0.1% (max) gain error and low 2mV (max) offset error, the LTC2656 could be used in high accuracy systems such as high-end optical networking, automated test equipment, precision instrumentation units, and data acquisition modules typically found in communication systems, industrial process control, automated test equipment (ATE) and programmable logic controllers.

The LTC2656 integrates a reference with a 2ppm/°C typical and 10ppm/°C maximum temperature coefficient. The integrated reference caters to demand for smaller parts in applications such as optical networking, where boards are already tightly packed.

Operating from a single 2.7V to 5.5V supply, supply current is 375uA per DAC with the reference activated. Output range is from either 0 to 2.5V, or 0 to 4.096V, depending on whether the designer chooses 16bit or 12bit resolution and an internal 1.25V or 2.048V reference. The low reference suits 3V systems and the high reference is for 5V systems. For designs that need the DACs to output up to 5V, a 2.5V external reference can be applied at the REFIN/OUT pin. The LTC2656 also includes a hardware option to power up the DAC outputs at zero-scale or midscale.

Additional features include a buffer on each DAC that shields the reference voltage from glitches caused by DAC switching and thus minimizing the DAC-to-DAC dynamic crosstalk. It is said to boast a low glitch impulse – important for AC applications such as waveform generation ” which reduces the transient voltages between code changes in the DAC. Along with a fast settling time (8.5us), this is said to reduce the harmonic distortion, making it possible to produce higher frequency, lower noise output waveforms.

The LTC2656 is offered in 20pin 4 x 5mm QFN or TSSOP packages, and there is a demo board now available. For more information, visit Linear’s website.

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