The OPA838 device is a rail-to-rail output op amp. Rail-to-rail output typically means that the output voltage swings to within 100 mV of the supply rails. There are different ways to specify this: one is with the output still in linear operation and another is with the output saturated. Saturated output voltages are closer to the power supply rails than linear outputs, but the signal is not a linear representation of the input. Saturation and linear operation limits are affected by the output current, where higher currents lead to more voltage loss in the output transistors; see Figure 6-56.

The specification tables show saturated output voltage specifications with a 2-kΩ load. Figure 6-11 and Figure 6-43 illustrate saturated voltage-swing limits versus output load resistance, and Figure 6-12 and Figure 6-44 illustrate the output saturation voltage versus load current. With a light load, the output voltage limits have constant headroom to the power rails and track the power supply voltages. For example, with a 1-kΩ load and a single 5-V supply, the linear output voltage ranges from 0.12 V to 4.88 V and ranges from 0.12 V to 2.58 V for a 2.7-V supply. The delta from each power supply rail is the same in each case: 0.12 V.

With devices like the OPA838 where the input range is lower than the output range, the input limits the available signal swing at low gains. Because the OPA838 is intended for higher gains, the smaller input swing range does not limit operation and full rail-to-rail output is available. Inverting voltage gain and transimpedance configurations are typically limited by the output voltage limits of the op amp if the noninverting input pin is biased in range.