LTC2754 LINER [Linear Technology], LTC2754 Datasheet - Page 21

• Manufacturer Part Number: LTC2754
• Description: Quad 12-/16-Bit SoftSpan IOUT DACs
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
the system’s specifi ed error budget. Select the amplifi er
from Table 6 and insert the specifi ed 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 fi nd the worst-case V
and I
the V
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 amplifi er
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
B
OS
over temperature. Then, plug these numbers into
and I
B
equations from Table 5 and calculate the
OS
applications: output voltage initial tolerance, output voltage
temperature coeffi cient 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 coeffi cient 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
coeffi cient, then the DAC output voltage along its transfer
characteristic will be very dependent on ambient conditions.
Minimizing the error due to reference temperature coef-
fi cient can be achieved by choosing a precision reference
with a low output voltage temperature coeffi cient 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 Specifi cations
REFERENCE
LT1019A-5,
LT1019A-10
LT1236A-5,
LT1236A-10
LT1460A-5,
LT1460A-10
LT1790A-2.5
LTC6652A-2.048
LTC6652A-2.5
LTC6652A-3
LTC6652A-3.3
LTC6652A-4.096
LTC6652A-5
TOLERANCE
±0.075%
±0.05%
±0.05%
±0.05%
±0.05%
INITIAL
TEMPERATURE
10ppm/°C
10ppm/°C
5ppm/°C
5ppm/°C
5ppm/°C
DRIFT
LTC2754
0.1Hz to 10Hz
2.1ppm
2.1ppm
2.1ppm
2.2ppm
2.3ppm
2.8ppm
12μV
20μV
12μV
3μV
NOISE
21
P-P
P-P
P-P
P-P
P-P
P-P
P-P
P-P
P-P
P-P
2754f