10
LTC1599
sn1599 1599fs
APPLICATIONS INFORMATION
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configured in unipolar or bipolar modes of operation
(Figures 1 and 3). These are the changes the op amp can
cause to the INL, DNL, unipolar offset, unipolar gain error,
bipolar zero and bipolar gain error. Table 4 contains a
partial list of LTC precision op amps recommended for use
with the LTC1599. The two sets of easy-to-use design
equations simplify the selection of op amps to meet the
system’s specified error budget. Select the amplifier from
Table 4 and insert the specified op amp parameters in
either Table 2 or Table 3. Add up all the errors for each
category to determine the effect the op amp has on the
accuracy of the LTC1599. Arithmetic summation gives an
(unlikely) worst-case effect. RMS summation produces a
more realistic effect.
Op amp offset will contribute mostly to output offset and
gain error and has minimal effect on INL and DNL. For the
LTC1599, a 500µV op amp offset will cause about 0.55LSB
INL degradation and 0.15LSB DNL degradation with a 10V
full-scale range (20V range in bipolar). For the LTC1599
configured in the unipolar mode, the same 500µV op amp
offset will cause a 3.3LSB zero-scale error and a 3.45LSB
gain error with a 10V full-scale range.
While not directly addressed by the simple equations in
Tables 2 and 3, temperature effects can be handled just as
easily for unipolar and bipolar applications. First, consult
an op amp’s data sheet to find the worst-case V
OS
and I
B
over temperature. Then, plug these numbers in the V
OS
and I
B
equations from Table 2 or Table 3 and calculate the
temperature induced effects.
For applications where fast settling time is important,
Application Note 74, entitled “
Component and Measure-
ment Advances Ensure 16-Bit DAC Settling Time
,” offers
a thorough discussion of 16-bit DAC settling time and op
amp selection.
Table 4. Partial List of LTC Precision Amplifiers Recommended for Use with the LTC1599, with Relevant Specifications
Amplifier Specifications
VOLTAGE CURRENT SLEW GAIN BANDWIDTH t
SETTLING
POWER
V
OS
I
B
A
OL
NOISE NOISE RATE PRODUCT with LTC1599 DISSIPATION
AMPLIFIER µV nA V/mV nV/√Hz pA/√Hz V/µs MHz µsmW
LT1001 25 2 800 10 0.12 0.25 0.8 120 46
LT1097 50 0.35 1000 14 0.008 0.2 0.7 120 11
LT1112 (Dual) 60 0.25 1500 14 0.008 0.16 0.75 115 10.5/Op Amp
LT1124 (Dual) 70 20 4000 2.7 0.3 4.5 12.5 19 69/Op Amp
LT1468 75 10 5000 5 0.6 22 90 2.5 117
Table 2. Easy-to-Use Equations Determine Op Amp Effects on DAC Accuracy in Unipolar Applications
OP AMP INL (LSB) DNL (LSB) UNIPOLAR OFFSET (LSB) UNIPOLAR GAIN ERROR (LSB)
V
OS
(mV) V
OS
• 1.2 • (10V/V
REF
)V
OS
• 0.3 • (10V/V
REF
)V
OS
• 6.6 • (10V/V
REF
)V
OS
• 6.9 • (10V/V
REF
)
I
B
(nA) I
B
• 0.00055 • (10V/V
REF
)I
B
• 0.00015 • (10V/V
REF
)I
B
• 0.065 • (10V/V
REF
)0
A
VOL
(V/V) 10k/A
VOL
3k/A
VOL
0 131k/A
VOL
Table 3. Easy-to-Use Equations Determine Op Amp Effects on DAC Accuracy in Bipolar Applications
OP AMP INL (LSB) DNL (LSB) BIPOLAR ZERO ERROR (LSB) BIPOLAR GAIN ERROR (LSB)
V
OS1
(mV) V
OS1
• 1.2 • (10V/V
REF
)V
OS1
• 0.3 • (10V/V
REF
)V
OS1
• 9.9 • (10V/V
REF
)V
OS1
• 6.9 • (10V/V
REF
)
I
B1
(nA) I
B1
• 0.00055 • (10V/V
REF
)I
B1
• 0.00015 • (10V/V
REF
)I
B1
• 0.065 • (10V/V
REF
)0
A
VOL1
10k/A
VOL
3k/A
VOL1
0 196k/A
VOL1
V
OS2
(mV) 0 0 V
OS2
• 6.7 • (10V/V
REF
)V
OS2
• 13.2 • (10V/V
REF
)
I
B2
(nA) 0 0 I
B2
• 0.065 • (10V/V
REF
)I
B2
• 0.13 • (10V/V
REF
)
A
VOL2
0 0 65k/A
VOL2
131k/A
VOL2
