OPA4191IPWT datasheet(28/65 Pages) TI2

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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 8-8. 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.

NCH3

PCH2

PCH1

IS1

NCH4

±Vsupply

+Vsupply

VIN+

VIN±

FUSE BANK

VOS TRIM

VOS DRIFT TRIM

e-Trim

TM Integrated Circuit

Figure 8-8. Rail-to-Rail Input Stage

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 8-9.

15.0

14.0

11.0

12.0

13.0

14.0

15.0

Common-Mode Voltage (V)

200

100

200

300

Input Offset Voltage vs Vcm

Without e-WULPŒ ,QWHJUDWHG &LUFXLW

Transition

Region

P-Channel

Region

N-Channel

Region

15.0

14.0

11.0

12.0

13.0

14.0

15.0

Common-Mode Voltage (V)

200

100

200

300

Transition

Region

P-Channel

Region

N-Channel

Region

OPAx191 e-WULPŒ 2SHUDWLRQDO $PSOLILHU

Input Offset Voltage vs Vcm

Figure 8-9. Common-Mode Transition vs Standard Rail-to-Rail Amplifiers

OPA191, OPA2191, OPA4191

SBOS701D – DECEMBER 2015 – REVISED AUGUST 2021

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