OPA333_17 Datasheet, PDF (18/42 Pages) Texas Instruments – 1.8-V, microPower, CMOS Operational Amplifiers, Zero-Drift Series

OPA333, OPA2333
SBOS351E – MARCH 2006 – REVISED DECEMBER 2015
Typical Applications (continued)
8.2.2.3 Application Curves
0.1
0.075
0.05
0.025
0
0
1
2
3
4
5
Input Voltage (V)
D002
Figure 23. Measured Transfer Function for Low-Level
Precision V-I
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100
80
60
40
20
0
–20
–40
–60
–80
–100
0
1
2
3
4
5
Desired Output Current, Iout_desired (µA)
D002
Figure 24. Calibrated Output Error for Low-Level V-I
8.2.3 Composite Amplifier
The circuit shown in Figure 25 is a composite amplifier used to drive the reference on the ADS8881. The
OPA333 provides excellent dc accuracy, and the THS4281 allows the output of the circuit to respond quickly to
the transient current requirements of a typical SAR data converter reference input. The ADS8881 system was
optimized for THD and achieved a measured performance of –110 dB. The linearity of the ADC is shown
Figure 26.
0.2
10µF
THS4281 _-
++
AVDD
20k
REFERENCE DRIVE CIRCUIT
1µF
1k
1µF
-
OPA333 ^{+ +}
AVDD
1k
1µF
AVDD
REF5045
Vout Vin
Temp
Trim Gnd
1µF
1K
VIN+
VCM
VIN-
1K
AVDD
THS4521
++-
10
-+
10nF
10
AVDD
REFP AVDD
AINP
V+
CONVST
ADS8881
AINM
GND
CONVST
1K
1K
INPUT DRIVER
18-Bit 1MSPS
SAR ADC
Figure 25. Composite Amplifier Reference Driver Circuit
18
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