4.1 mA

2.2 mA

10

OPA2863

SBOS982A – JUNE 2020 – REVISED JUNE 2020

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8.3 Feature Description

8.3.1 Input Stage

The OPAx863 devices include a rail-to-rail input stage. The main stage differential pair using PNP bipolar

+ 0.2 V. The PNP and NPN input stages offer a gain-bandwidth product of 50 MHz and a voltage noise density

of 5.9 nV/

√Hz. The offset voltage for the two input stages is matched to lie within the device specifications. The

NPN input stage does not use the slew boost circuit during large-signal transient response. The input bias

current for the PNP and NPN input stages is opposite in polarity, which adds an additional offset based on the

values of the gain-setting and feedback resistors. A common-mode input voltage transition between these input

stages will cause a crossover distortion which needs to be considered in high-frequency applications requiring

across process and ambient temperature .

Since the OPAx863 devices are bipolar amplifiers, the two inputs are protected with anti-parallel back-to-back

diodes between them, which limits the maximum input differential voltage to 1 V. In very fast input or output

transient conditions, the amplifier is slew limited and the two inputs are puled apart up to 1 V when the anti-

parallel diodes begin to conduct. Care must be taken to use gain-setting and feedback resistors large enough to

limit the current through these diodes in such conditions.

8.3.2 Output Stage

Violating the output headroom to either of the supplies will cause output signal clipping and degrade linear

performance.

The OPAx863 devices integrate an output short-circuit protection circuit which makes the device rugged for use

in real-world applications.

8.3.2.1 Overload Power Limit

The OPAx863 devices include overload power limiting which limits the increase in device quiescent current with

output saturated to either of the supplies. Typically, when an amplifier's output saturates, its two inputs are pulled

apart which may enable the slew boost circuit. The input differential voltage is an error voltage in negative

feedback, which the amplifier core nullifies by engaging the slew boost circuit and driving the output stage deeper

gain) drops with increase in its base and collector current, increasing the device quiescent current. This may

cause a catastrophic failure in multi-channel, high-gain, high-density front-end designs and reduce operating

lifetime in portable battery powered systems. The OPAx863 devices overload power limiting includes an

intelligent output saturation detection circuit which limits the devices quiescent current to 2.2-mA per channel

under DC overload condition. This increase in quiescent current is smaller with AC input or output with output

saturation duration for only a fraction of the overall signal time period.

Figure 6. Increase in Quiescent Current with Output Saturation