OPA2991IDSGR datasheet(22/78 Pages) TI

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7.3 Feature Description

7.3.1 Input Protection Circuitry

The OPAx991 uses a unique input architecture to eliminate the requirement for input protection diodes but still

provides robust input protection under transient conditions. Figure 7-1 shows conventional input diode protection

schemes that are activated by fast transient step responses and introduce signal distortion and settling time

delays because of alternate current paths, as shown in Figure 7-2. For low-gain circuits, these fast-ramping input

signals forward-bias back-to-back diodes, causing an increase in input current and resulting in extended settling

time.

OPAx991

40 V

~0.7 V

VOUT

V+

Conventional Input Protection

Limits Differential Input Range

OPAx991 Provides Full 40-V

Differential Input Range

VIN+

VIN

VOUT

V+

VIN+

VIN

Figure 7-1. OPAx991 Input Protection Does Not Limit Differential Input Capability

Input Low-Pass Filter

Ron_mux

Sn+1

Simplified Mux Model

RFILT

CFILT

Vn = 10 V

Vn+1 = ±10 V

10 V

±10 V

Buffer Amplifier

Idiode_transient

10 V

~±9.3 V

VIN+

VIN±

~0.7 V

VOUT

±10 V

Ron_mux

Figure 7-2. Back-to-Back Diodes Create Settling Issues

The OPAx991 family of operational amplifiers provides a true high-impedance differential input capability for

high-voltage applications using a patented input protection architecture that does not introduce additional signal

distortion or delayed settling time, making the device an optimal op amp for multichannel, high-switched, input

applications. The OPA991 tolerates a maximum differential swing (voltage between inverting and non-inverting

pins of the op amp) of up to 40 V, making the device suitable for use as a comparator or in applications

with fast-ramping input signals such as data-acquisition systems; see the TI TechNote MUX-Friendly Precision

Operational Amplifiers for more information.

7.3.2 EMI Rejection

The OPAx991 uses integrated electromagnetic interference (EMI) filtering to reduce the effects of EMI from

sources such as wireless communications and densely-populated boards with a mix of analog signal chain and

digital components. EMI immunity can be improved with circuit design techniques; the OPAx991 benefits from

these design improvements. Texas Instruments has developed the ability to accurately measure and quantify the

immunity of an operational amplifier over a broad frequency spectrum extending from 10 MHz to 6 GHz. Figure

7-3 shows the results of this testing on the OPAx991. Table 7-1 shows the EMIRR IN+ values for the OPAx991 at

particular frequencies commonly encountered in real-world applications. The EMI Rejection Ratio of Operational

OPA991, OPA2991, OPA4991

SBOS969F – OCTOBER 2019 – REVISED JANUARY 2022

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