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LTC2755 Datasheet(PDF) 19 Page - Linear Technology |
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LTC2755 Datasheet(HTML) 19 Page - Linear Technology |
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19 / 24 page  LTC2755 19 2755f APPLICATIONS INFORMATION Op amp offset will contribute mostly to output offset and gain error, and has minimal effect on INL and DNL. For example, for the LTC2755-16 with a 5V reference in 5V unipolar mode, a 250μV op amp offset will cause a 3.3LSB zero-scale error and a 3.3LSB gain error; but only 0.8LSB of INL degradation and 0.2LSB of DNL degradation. While not directly addressed by the simple equations in Tables 4 and 5, temperature effects can be handled just as easily for unipolar and bipolar applications. First, con- sult an op amp’s data sheet to find the worst-case VOS and IB over temperature. Then, plug these numbers into the VOS and IB equations from Table 5 and calculate the temperature-induced effects. For applications where fast settling time is important, Ap- plication Note 74, Component and Measurement Advances Ensure 16-Bit DAC Settling Time, offers a thorough discus- sion of 16-bit DAC settling time and op amp selection. Precision Voltage Reference Considerations Much in the same way selecting an operational amplifier for use with the LTC2755 is critical to the performance of the system, selecting a precision voltage reference also requires due diligence. The output voltage of the LTC2755 is directly affected by the voltage reference; thus, any voltage reference error will appear as a DAC output volt- age error. There are three primary error sources to consider when selecting a precision voltage reference for 16-bit appli- cations: output voltage initial tolerance, output voltage temperature coefficient and output voltage noise. Initial reference output voltage tolerance, if uncorrected, generates a full-scale error term. Choosing a reference with low output voltage initial tolerance, like the LT1236 (±0.05%), minimizes the gain error caused by the reference; however, a calibration sequence that corrects for system zero- and full-scale error is always recommended. A reference’s output voltage temperature coefficient af- fects not only the full-scale error, but can also affect the circuit’s apparent INL and DNL performance. If a refer- ence is chosen with a loose output voltage temperature coefficient, then the DAC output voltage along its transfer characteristic will be very dependent on ambient conditions. Minimizing the error due to reference temperature coef- ficient can be achieved by choosing a precision reference with a low output voltage temperature coefficient and/or tightly controlling the ambient temperature of the circuit to minimize temperature gradients. As precision DAC applications move to 16-bit and higher performance, reference output voltage noise may con- tribute a dominant share of the system’s noise floor. This in turn can degrade system dynamic range and signal-to- noise ratio. Care should be exercised in selecting a voltage reference with as low an output noise voltage as practi- cal for the system resolution desired. Precision voltage references, like the LT1236, produce low output noise in the 0.1Hz to 10Hz region, well below the 16-bit LSB level in 5V or 10V full-scale systems. However, as the circuit bandwidths increase, filtering the output of the reference may be required to minimize output noise. Table 7. Partial List of LTC Precision References Recommended for Use with the LTC2755 with Relevant Specifications REFERENCE INITIAL TOLERANCE TEMPERATURE DRIFT 0.1Hz to 10Hz NOISE LT1019A-5, LT1019A-10 ±0.05% 5ppm/°C 12μVP-P LT1236A-5, LT1236A-10 ±0.05% 5ppm/°C 3μVP-P LT1460A-5, LT1460A-10 ±0.075% 10ppm/°C 20μVP-P LT1790A-2.5 ±0.05% 10ppm/°C 12μVP-P |
Similar Part No. - LTC2755_15 |
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Similar Description - LTC2755_15 |
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