Datasheet

LTC2757
15
2757f
Op Amp Selection
Because of the extremely high accuracy of the 18-bit
LTC2757, 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 3 and 4 contain equations for evaluating the ef-
fects of op amp parameters on the LTC2757’s accuracy.
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 3. Coeffi cients for the Equations of Table 4
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 4. 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.
OP
AMP
INL (LSB) DNL (LSB) UNIPOLAR
OFFSET (LSB)
BIPOLAR ZERO ERROR
(LSB)
UNIPOLAR GAIN
ERROR (LSB)
BIPOLAR GAIN
ERROR (LSB)
V
OS1
(mV)
V
OS1
•12.1•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
V
OS1
•3.1•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
A3•V
OS1
•52.4•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
A3•V
OS1
•78.6•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
V
OS1
•52.4•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
V
OS1
•52.4•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
I
B1
(nA)
I
B1
•0.0012•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
I
B1
•0.00032•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
I
B1
•0.524•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
I
B1
•0.524•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
I
B1
•0.0072•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
I
B1
•0.0072•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
A
VOL1
(V/mV)
A1•
66
A
VOL1
⎛
⎝
⎜
⎞
⎠
⎟
A2•
6
A
VOL1
⎛
⎝
⎜
⎞
⎠
⎟
00
A5•
524
A
VOL1
⎛
⎝
⎜
⎞
⎠
⎟
A5•
524
A
VOL1
⎛
⎝
⎜
⎞
⎠
⎟
V
OS2
(mV)
00 0
A4•V
OS2
•52.4•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
V
OS2
•104.8•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
V
OS2
•104.8•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
I
B2
(nA)
00 0
A4•I
B2
•0.524•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
I
B2
•1.048•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
I
B2
•1.048•
5V
V
REF
⎛
⎝
⎜
⎞
⎠
⎟
A
VOL2
(V/mV)
00 0
A4•
262
A
VOL2
⎛
⎝
⎜
⎞
⎠
⎟
524
A
VOL2
⎛
⎝
⎜
⎞
⎠
⎟
524
A
VOL2
⎛
⎝
⎜
⎞
⎠
⎟