Typically, input bias current is approximately ±30 pA. Input voltages exceeding the power supplies, however, can

cause excessive current to flow into or out of the input pins. Momentary voltages greater than the power supply

can be tolerated if the input current is limited to 10 mA. This limitation is easily accomplished with an input

resistor, as shown in Figure 7-3.

10 mA max

5 NŸ

+5V

Current-limiting resistor

required if input voltage

exceeds supply rails by

> 0.3V.

Copyright © 2016, Texas Instruments Incorporated

Figure 7-3. Input Current Protection

7.3.3 Input Differential Voltage

The typical input bias current of the OPA388-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 the 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

7.3.4 Internal Offset Correction

The OPA388-Q1 operational amplifier uses an auto-calibration technique with a time-continuous, 200-kHz

operational amplifier in the signal path. This amplifier is zero-corrected every 5 µs using a proprietary technique.

no aliasing or flicker noise.

7.3.5 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 OPA388-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 OPA388-Q1 has a single functional mode and is operational when the power-supply voltage is greater than

2.5 V (±1.25 V). The maximum specified power-supply voltage for the OPA388-Q1 is 5.5 V (±2.75 V).

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OPA388-Q1

SBOS989 – AUGUST 2020

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Product Folder Links: OPA388-Q1