OPA992 datasheet(23/50 Pages) TI

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7.3.5 Common-Mode Voltage Range

The OPAx992-Q1 is a 40-V, true rail-to-rail input operational amplifier with an input common-mode range

that extends to both supply rails. This wide range is achieved with paralleled complementary N-channel and

P-channel differential input pairs, as shown in Figure 7-8. The N-channel pair is active for input voltages close

to the positive rail, typically from (V+) – 1 V to the positive supply. The P-channel pair is active for inputs from

the negative supply to approximately (V+) – 2 V. There is a small transition region, typically (V+) – 2 V to (V+)

– 1 V, in which both input pairs are on. This transition region can vary modestly with process variation. Within

this region PSRR, CMRR, offset voltage, offset drift, noise, and THD performance may be degraded compared

to operation outside this region.

Figure 6-5 shows this transition region for a typical device in terms of input voltage offset in more detail.

For more information on common-mode voltage range and PMOS/NMOS pair interaction, see Op Amps With

Complementary-Pair Input Stages application note.

NMOS

PMOS

NMOS

V-

V+

IN+

IN-

Figure 7-8. Rail-to-Rail Input Stage

7.3.6 Phase Reversal Protection

The OPAx992-Q1 family has internal phase-reversal protection. Many op amps exhibit a phase reversal when

the input is driven beyond the linear common-mode range. This condition is most often encountered in non-

inverting circuits when the input is driven beyond the specified common-mode voltage range, causing the output

to reverse into the opposite rail. The OPAx992-Q1 is a rail-to-rail input op amp; therefore, the common-mode

range can extend up to the rails. Input signals beyond the rails do not cause phase reversal; instead, the output

limits into the appropriate rail. Figure 7-9 shows this performance. For more information on phase reversal, see

Op Amps With Complementary-Pair Input Stages application note.

Time (25µs/div)

D031

Input

Output

Figure 7-9. No Phase Reversal

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OPA992-Q1, OPA2992-Q1, OPA4992-Q1

SBOSAC9D – AUGUST 2022 – REVISED APRIL 2023

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