OPA2172 Datasheet, PDF (26/42 Pages) Texas Instruments – OPAx172 36-V, Single-Supply, 10-MHz, Rail-to-Rail Output Operational Amplifiers

OPA172, OPA2172, OPA4172
SBOS618H – DECEMBER 2013 – REVISED SEPTEMBER 2015
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9.2.1.3 Application Curve
The OPA172 meets the supply voltage requirements of 30 V. The OPA172 is tested for various capacitive loads
and R_ISO is adjusted to get an overshoot corresponding to Table 4. The results of the these tests are summarized
in Figure 49.
1000
60°Phase Margin
45°Phase Margin
100
10
1
0.01
0.1
1
10
100
C_LOAD (nF)
Figure 49. R_ISO vs C_LOAD
1000
C041
9.2.2 Bidirectional Current Source
The improved Howland current-pump topology shown in Figure 50 provides excellent performance because of
the extremely tight tolerances of the on-chip resistors of the INA132. By buffering the output using an OPA172,
the output current the circuit is able to deliver is greatly extended.
The circuit dc transfer function is shown in Equation 2:
I_OUT = V_IN / R1
(2)
The OPA172 can also be used as the feedback amplifier because the low bias current minimizes error voltages
produced across R1. However, for improved performance, select a FET-input device with extremely low offset,
such as the OPA192, OPA140, or OPA188 as the feedback amplifier.
INA132
±IN
40 NŸ
40 NŸ
SENSE
VIN
+IN
40 NŸ
+
40 NŸ
OUTPUT
REF
VCC
+ ₊ ^OPA172
VEE
VCC
OPA172 _{+ +}
VEE
R1
IOUT
Figure 50. Bidirectional Current Source
26
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