Electronicdesign 2381 Xl 18bit

18-Bit DAC Provides Precision, Linearity, And Output Flexibility

March 18, 2010
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Linear Technology’s LTC2757 18-bit DAC

In addition to 18-bit resolution and remarkable dynamic performance specifications, Linear Technology’s LTC2757 parallel-output, multiplying digital-to-analog converter (DAC) offers two unusual features: current-output and register-programmable output-voltage ranges.

Providing current rather than voltage output allows custom-fitting output amplifiers appropriate to each application. This makes it possible to provide wider output voltage output swings than possible using voltage-mode DACs, in which the DAC’s dc supply constrains the output voltage range. It also enables designers who work with the DAC to optimize the amplifier on the basis of their application’s need for speed, accuracy, noise, power, and other factors.

Being able to program different output ranges, (0 to 5 V, 0 to 10 V, ±10 V, ±5 V, ±2.5 V, and –2.5 to 7.5 V) makes it unnecessary to add precision gain stages. The output range is selected either via a serial interface or, if on-the-fly selection is not needed, by pin-strapping. At power-on, the DAC output is reset to 0 V regardless of output range. It can also be reset by the use of a CLR pin.

Intended for high-performance instrumentation, automated test equipment, data acquisition systems, and medical devices, the DAC has impressive dynamic specs: guaranteed maximum integral and differential nonlinearity of  ±1 LSB and 2.1-µs full-scale settling time. Glitch impulse is specified as 1.4 nV • s.

The LTC2757’s bidirectional parallel input/output interface allows both programming and readback of the DAC output span setting as well as the contents of other internal registers. Voltage-controlled offset and gain adjustment pins provide the ability to null system offset, gain error, or reference errors.

The LTC2757 DAC comes in a 7- by 7-mm, 48-pin leaded quad-flatpack. Unit pricing begins at $25.50.

Linear Technology


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