LTC2754_15 datasheet(21/28 Pages) LINER

21 / 28 page

LTC2754

2754f

APPLICATIONS INFORMATION

the system’s speciﬁed error budget. Select the ampliﬁer

from Table 6 and insert the speciﬁed op amp parameters

in Table 5. Add up all the errors for each category to de-

termine the effect the op amp has on the accuracy of the

part. Arithmetic summation gives an (unlikely) worst-case

effect. A root-sum-square (RMS) summation produces a

more realistic estimate.

Op amp offset will contribute mostly to output offset and

gain error, and has minimal effect on INL and DNL. For

example, for the LTC2754-16 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 LTC2754 is critical to the performance of

the system, selecting a precision voltage reference also

requires due diligence. The output voltage of the LTC2754

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

applications: 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.

Table 7. Partial List of LTC Precision References Recommended

for Use with the LTC2754 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

LTC6652A-2.048

±0.05%

5ppm/°C

2.1ppmP-P

LTC6652A-2.5

2.1ppmP-P

LTC6652A-3

2.1ppmP-P

LTC6652A-3.3

2.2ppmP-P

LTC6652A-4.096

2.3ppmP-P

LTC6652A-5

2.8ppmP-P

LTC2754 Datasheet(PDF) 21 Page - Linear Technology

LTC2754 Datasheet(HTML) 21 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Datasheet Download

Link URL