7.3 Feature Description

7.3.1 Input Bias Current

During normal operation, the typical input bias current of the OPAx387 is 30 pA. The device exhibits low drift

over the full temperature range of –40°C to +125°C. There are no antiparallel diodes between the input pins

(+IN and –IN); therefore, the differential input maximum voltage is limited only by diodes connected to the

supply voltage pins. However, use caution in cases where the input differential voltage exceeds the nominal

operating input differential voltage. When inputs are separated, the switching offset-cancellation path internal to

the amplifier exceeds normal operating conditions, and can potentially create long settling behavior upon return

to normal operation. The equivalent input circuit of OPAx387 is shown in Figure 7-1.

+

–

CORE

450

450

+IN

–IN

V+

V–

Figure 7-1. Equivalent Input Circuit

7.3.2 EMI Susceptibility and Input Filtering

Operational amplifiers can exhibit sensitivity to electromagnetic interference (EMI). Typically, conducted EMI

(that is, EMI that enters the device through conduction) is more commonly observed than radiated EMI (that

is, EMI that enters the device through radiation). When conducted EMI enters the operational amplifier, the

dc offset at the amplifier output can shift from the nominal value. 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 OPAx387 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 conducted EMI rejection of the OPAx387 is seen in

Figure 7-2.

Frequency (Hz)

20

30

40

50

60

70

80

90

100

110

120

130

140

10M

100M

1G

5G

c104

Figure 7-2. EMI Rejection Ratio

7.4 Device Functional Modes

The OPAx387 have a single functional mode and are operational when the power-supply voltage is greater than

1.7 V (±0.85 V). The maximum specified power-supply voltage for the OPAx387 is 5.5 V (±2.75 V).

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OPA387, OPA2387, OPA4387

SBOS984F – NOVEMBER 2020 – REVISED FEBRUARY 2022

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