OPA191_017 Datasheet, PDF (23/51 Pages) Texas Instruments – 36-V, Low Power, Precision, CMOS, Rail-to-Rail Input/Output, Low Offset Voltage, Low Input Bias Current Op Amp

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OPA191, OPA2191, OPA4191
SBOS701A – DECEMEBER 2015 – REVISED APRIL 2016
8.3 Feature Description
8.3.1 Input Protection Circuitry
The OPAx191 uses a unique input architecture to eliminate the need for input protection diodes but still provides
robust input protection under transient conditions. Conventional input diode protection schemes shown in
Figure 51 can be activated by fast transient step responses and can introduce signal distortion and settling time
delays because of alternate current paths, as shown in Figure 52. For low-gain circuits, these fast-ramping input
signals forward-bias back-to-back diodes that cause an increase in input current, resulting in extended settling
time.
V+
V+
VIN+
VIN
36 V
OPAx191
VOUT
VIN+
VIN
~0.7 V
VOUT
V
OPAx191 Provides Full 36-
V Differential Input Range
V
Conventional Input Protection
Limits Differential Input Range
Figure 51. OPA191 Input Protection Does Not Limit Differential Input Capability
Vn = +10 V R_FILT
+10 V
C_FILT
Vn+1 = ±10 V R_FILT
±10 V
C_FILT
Input Low Pass Filter
S_n
C_S
R_{on_mux}
1
D
1
2
+10 V
~±9.3 V
C_D
S_n+1
R_{on_mux}
2
Vin±
C_S
I_{diode_transient}
~0.7 V
Vin+
±10 V
Vout
Simplified Mux Model
Buffer Amplifier
Figure 52. Back-to-Back Diodes Create Settling Issues
The OPAx191 family of operational amplifiers provides a true high-impedance differential input capability for high-
voltage applications. This patented input protection architecture does not introduce additional signal distortion or
delayed settling time, making the device an optimal op amp for multichannel, high-switched, input applications.
The OPA191 can tolerate a maximum differential swing (voltage between inverting and noninverting pins of the
op amp) of up to 36 V, making the device suitable for use as a comparator or in applications with fast-ramping
input signals such as multiplexed data-acquisition systems (see Figure 64.
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