Datasheet

LTC2758
18
2758fa
For more information www.linear.com/LTC2758
Op Amp Selection
Because of the extremely high accuracy of the 18-bit
LTC2758, careful thought should be given to op amp
selection in order to achieve the exceptional performance
of which the part is capable. Fortunately, the sensitivity of
INL and DNL to op amp offset has been greatly reduced
compared to previous generations of multiplying DACs.
Tables 4 and 5 contain equations for evaluating the ef-
fects of op amp parameters on the LTC2758’s accuracy
when programmed in a unipolar or bipolar output range.
These are the changes the op amp can cause to the INL,
DNL, unipolar offset, unipolar gain error, bipolar zero and
bipolar gain error.
APPLICATIONS INFORMATION
Table 5. Easy-to-Use Equations Determine Op Amp Effects on DAC Accuracy in All Output Ranges (Circuit of Page 1). Subscript 1
Refers to Output Amp, Subscript 2 Refers to Reference Inverting Amp.
Table 4. Coefficients for the Equations of Table 5
OUTPUT RANGE A1 A2 A3 A4 A5
5V 1.1 2 1 1
10V 2.2 3 0.5 1.5
±5V 2 2 1 1 1.5
±10V 4 4 0.83 1 2.5
±2.5V 1 1 1.4 1 1
–2.5V to 7.5V 1.9 3 0.7 0.5 1.5
Table 6 contains a partial list of LTC precision op amps
recommended for use with the LTC2758. The easy-to-use
design equations simplify the selection of op amps to meet
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.
A3•V
OS1
•78.6•
I
B1
•0.524•
0
A4•V
OS2
•52.4•
A4•I
B2
•0.524•
A4•
( )
5V
V
REF
( )
5V
V
REF
( )
66
A
VOL1
OP AMP
V
OS1
(mV)
I
B1
(nA)
A
VOL1
(V/mV)
V
OS2
(mV)
I
B2
(nA)
A
VOL2
(V/mV)
V
OS1
•12.1•
I
B1
•0.0012•
A1•
0
0
0
INL (LSB)
( )
5V
V
REF
( )
5V
V
REF
( )
6
A
VOL1
( )
262
A
VOL2
( )
524
A
VOL1
( )
524
A
VOL1
( )
524
A
VOL2
( )
524
A
VOL2
V
OS1
•3.1•
I
B1
•0.00032•
A2•
0
0
0
DNL (LSB)
( )
5V
V
REF
( )
5V
V
REF
A3•V
OS1
•52.4•
I
B1
•0.524•
0
0
0
0
UNIPOLAR
OFFSET (LSB)
( )
5V
V
REF
( )
5V
V
REF
( )
5V
V
REF
V
OS1
•52.4•
I
B1
•0.0072•
A5•
V
OS2
•104.8•
I
B2
•1.048•
BIPOLAR GAIN
ERROR (LSB)
( )
5V
V
REF
( )
5V
V
REF
( )
5V
V
REF
( )
5V
V
REF
BIPOLAR ZERO
ERROR (LSB)
UNIPOLAR GAIN
ERROR (LSB)
( )
5V
V
REF
( )
5V
V
REF
( )
5V
V
REF
( )
5V
V
REF
( )
5V
V
REF
V
OS1
•52.4•
I
B1
•0.0072•
A5•
V
OS2
•104.8•
I
B2
•1.048•
Table 6. Partial List of LTC Precision Amplifiers Recommended for Use with the LTC2758 with Relevant Specifications
AMPLIFIER
AMPLIFIER SPECIFICATIONS
V
OS
µV
I
B
nA
A
VOL
V/mV
VOLTAGE
NOISE
nV/√Hz
CURRENT
NOISE
pA/√Hz
SLEW
RATE
V/µs
GAIN BANDWIDTH
PRODUCT
MHz
t
SETTLING
with LTC2758
µs
POWER
DISSIPATION
mW
LTC1150 10 0.05 5600 90 0.0018 3 2.5 10ms 24
LT1001 25 2 800 10 0.12 0.25 0.8 120 46
LT1012 25 0.1 2000 14 0.02 0.2 1 120 11.4
LT1097 50 0.35 2500 14 0.008 0.2 0.7 120 11
LT1468 75 10 5000 5 0.6 22 90 2.1 117