7.3.2 Input Differential Voltage

The typical input bias current of the OPAx388-Q1 during normal operation is approximately 30 pA. In overdriven

conditions, the bias current can increase significantly. The most common cause of an overdriven condition

occurs when an operational amplifier is outside of the linear range of operation. When the output of the

operational amplifier is driven to one of the supply rails, the feedback loop requirements cannot be satisfied

and a differential input voltage develops across the input pins. This differential input voltage results in activation

of parasitic diodes inside the front-end input chopping switches that combine with 10-kΩ electromagnetic

interference (EMI) filter resistors to create the equivalent circuit shown in Figure 7-4. Notice that the input bias

current remains within specification in the linear region.

CORE

-In

+In

Clamp

100 W

100 W

Copyright © 2016, Texas Instruments Incorporated

Figure 7-4. Equivalent Input Circuit

7.3.3 Internal Offset Correction

The OPAx388-Q1 operational amplifiers use an auto-calibration technique with a time-continuous, 200-kHz

operational amplifier in the signal path. These amplifiers are zero-corrected every 5 µs using a proprietary

design has no aliasing or flicker noise.

7.3.4 EMI Susceptibility and Input Filtering

Operational amplifiers vary in susceptibility to EMI. If conducted EMI enters the operational amplifier, the dc

offset at the amplifier output can shift from its nominal value when EMI is present. This shift is a result of signal

rectification associated with the internal semiconductor junctions. Although all operational amplifier pin functions

can be affected by EMI, the input pins are likely to be the most susceptible. The OPAx388-Q1 operational

amplifier family incorporates an internal input low-pass filter that reduces the amplifier response to EMI. Both

common-mode and differential-mode filtering are provided by the input filter. The filter is designed for a cutoff

frequency of approximately 20 MHz (–3 dB), with a rolloff of 20 dB per decade.

7.4 Device Functional Modes

The OPAx388-Q1 have a single functional mode and are operational when the power-supply voltage is greater

than 2.5 V (±1.25 V). The maximum specified power-supply voltage for the OPAx388-Q1 is 5.5 V (±2.75 V).

OPA388-Q1, OPA2388-Q1

SBOS989A – AUGUST 2020 – REVISED NOVEMBER 2021

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