OP249_15 Datasheet, PDF (15/20 Pages) Analog Devices – Precision JFET, High Speed, Dual Operational Amplifier

Data Sheet
OP249
DAC OUTPUT AMPLIFIER
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.
Because the DAC output capacitance appears at the inputs of
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.
V_DD
0.1µF
75Ω
REFERENCE
OR V_IN
18
20
V_DD
R_FB
OUT₁ 1
500Ω ^{19 VREF}
PM7545
AGND 2
DB₁₁ TO DB₀ ^DGND
3
12
DATA INPUT
C
33pF
+15V
0.1µF
2
8
1/2
OP249
1
3
4 0.1µF
–15V
V_OUT
Figure 47. Fast Settling and Low Offset Error of the OP249 Enhances CMOS DAC Performance—Unipolar Operation
R4
20kΩ
1%
REFERENCE
OR V_IN
V_DD
0.1µF
75Ω
500Ω
18
20
V_DD
R_FB
OUT₁ 1
19 V_{REF PM7545}
AGND 2
DB₁₁ TO DB₀ ^DGND
3
12
DATA INPUT
C
33pF
+15V
0.1µF
2
8
1/2
OP249
1
3
R3
10kΩ
1%
R5
10kΩ
1%
5
1/2
OP249 ⁷
6 ₄ 0.1µF
–15V
V_OUT
Figure 48. Fast Settling and Low Offset Error of the OP249 Enhances CMOS DAC Performance—Bipolar Operation
Rev. H | Page 15 of 20