Data Sheet
OP249
Because the DAC output capacitance appears at the inputs of
DAC OUTPUT AMPLIFIER
the op amp, it is essential that the amplifier be adequately
compensated. Compensation increases the phase margin and
ensures an optimal overall settling response. The required lead
compensation is achieved with Capacitor C in Figure 48.
Unity-gain stability, a low offset voltage of 300 µV typical, and a
fast settling time of 870 ns to 0.01%, makes the OP249 an ideal
amplifier for fast DACs.
For CMOS DAC applications, the low offset voltage of the OP249
results in excellent linearity performance. CMOS DACs, such as
the PM7545, typically have a code-dependent output resistance
variation between 11 kΩ and 33 kΩ. The change in output
resistance, in conjunction with the 11 kΩ feedback resistor, results
in a noise gain change, which causes variations in the offset
error, increasing linearity errors. The OP249 features low offset
voltage error, minimizing this effect and maintaining 12-bit
linearity performance over the full-scale range of the converter.
V
DD
75Ω
0.1µF
C
+15V
33pF
0.1µF
18
20
V
R
DD
FB
OUT
1
2
2
8
1
REFERENCE
1/2
19
V
V
PM7545
1
REF
OUT
OR V
OP249
IN
500Ω
3
AGND
4
0.1µF
DGND
3
DB TO DB
11
0
–15V
12
DATA INPUT
Figure 47. Fast Settling and Low Offset Error of the OP249 Enhances CMOS DAC Performance—Unipolar Operation
R4
20kΩ
1%
V
DD
R5
10kΩ
1%
75Ω
0.1µF
C
+15V
33pF
18
20
0.1µF
1
V
R
DD
R3
10kΩ
1%
FB
8
1
2
2
OUT
1
1/2
OP249
REFERENCE
19
V
5
6
PM7545
REF
OR V
IN
500Ω
1/2
OP249
3
AGND
V
7
OUT
DGND
DB TO DB
0.1µF
4
11
0
3
12
DATA INPUT
–15V
Figure 48. Fast Settling and Low Offset Error of the OP249 Enhances CMOS DAC Performance—Bipolar Operation
Rev. I | Page 15 of 18
ADI [ ADI ]
