OPA191_017 Datasheet, PDF (28/51 Pages) Texas Instruments – 36-V, Low Power, Precision, CMOS, Rail-to-Rail Input/Output, Low Offset Voltage, Low Input Bias Current Op Amp

OPA191, OPA2191, OPA4191
SBOS701A – DECEMEBER 2015 – REVISED APRIL 2016
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8.3.6 Common-Mode Voltage Range
The OPAx191 is a 36-V, true rail-to-rail input operational amplifier with an input common-mode range that
extends 100 mV beyond either supply rail. This wide range is achieved with paralleled complementary N-channel
and P-channel differential input pairs, as shown in Figure 58. The N-channel pair is active for input voltages
close to the positive rail, typically (V+) – 3 V to 100 mV above the positive supply. The P-channel pair is active
for inputs from 100 mV below the negative supply to approximately (V+) – 1.5 V. There is a small transition
region, typically (V+) –3 V to (V+) – 1.5 V in which both input pairs are active. This transition region varies
modestly with process variation. Within this region PSRR, CMRR, offset voltage, offset drift, noise, and THD
performance are degraded compared to operation outside this region.
+Vsupply
IS1
e-Trim^TM
VIN-
PCH1
VIN+
PCH2 ^NCH3
NCH4
FUSE BANK
VOS TRIM VOS DRIFT TRIM
Figure 58. Rail-to-Rail Input Stage
-Vsupply
To achieve the best performance for two-stage rail-to-rail input amplifiers, avoid the transition region when
possible. The OPAx191 uses a precision trim for both the N-channel and P-channel regions. This technique
enables significantly lower levels of offset than previous-generation devices, causing variance in the transition
region of the input stages to appear exaggerated relative to offset over the full common-mode range, as shown in
Figure 59.
P-Channel
Region
Transition
Region
N-Channel
Region
P-Channel Transition
Region
Region
N-Channel
Region
200
200
100
100
0
0
±100
±200
OPAx191 e-Trim
Input Offset Voltage vs Vcm
±300
±15.0 ±14.0
« 11.0 12.0 13.0
Common-Mode Voltage (V)
14.0 15.0
±100
±200
Input Offset Voltage vs Vcm
without e-Trim Input
±300
±15.0 ±14.0 « 11.0 12.0 13.0
Common-Mode Voltage (V)
14.0 15.0
Figure 59. Common-Mode Transition vs Standard Rail-to-Rail Amplifiers
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