Keep the internal gain network distinct from the external resistor
The INA826 uses an external gain-setting resistor together with internal feedback elements. TI describes the internal resistors as trimmed to accurate absolute values, with their accuracy and temperature behavior included in the device's gain specifications. The external resistor participates in the resulting gain but brings its own accuracy and stability. A nominal RG value therefore describes one element of a combined gain-setting relationship.
Unity-gain operation has a distinct basis: the external gain-setting resistor is omitted. The internal differential-amplifier network then remains responsible for the named gain behavior. This differs from treating unity gain as a request for an arbitrary zero-valued or shorted external element. The absence of RG is meaningful because it changes which gain-setting contributions are present, rather than merely changing the label attached to the same network.
For operation using RG, a component-level gain-accuracy statement and the external resistor's contribution must remain distinguishable. The internal trimming does not assign accuracy to the added element. Conversely, the external resistor's tolerance does not replace the manufacturer's characterization of its own internal network. A useful gain comparison preserves both sources of behavior, so the requested gain and the origin of its accuracy are understood together.
Compare gain drift on the actual gain basis
Initial gain error describes a deviation at a stated condition, while gain drift describes how that relationship changes with temperature. The INA826 discussion treats those quantities separately. A correction established at one temperature can remove an initial static error without making the gain-setting elements track each other identically as temperature changes. The physical sources of drift remain present after that initial correction.
TI gives unity-gain operation and operation with RG different temperature contexts. Without the external resistor, the gain-drift account rests on matching within the internal differential-amplifier network. With RG present, the internal feedback resistors' temperature behavior is considered relative to that of the external element. Thus changing the gain basis changes the contributors that must be compared, even though the device name remains the same.
The error-source discussion also separates static accuracy from temperature-dependent change. Those descriptions should travel with the actual gain configuration rather than with a general calibrated label. Two configurations can start from corrected output readings while retaining different drift relationships. Understanding this distinction identifies why the chosen gain and external resistor matter over temperature, without treating a calibration at one condition as evidence that all later gain settings have the same error behavior.
Account for gain-pin resistance and capacitance as different errors
At higher gain, the required external gain resistance becomes smaller. TI explains that connection resistance can then become an appreciable part of the gain-setting path. Wiring and socket resistance belong to the relationship because they accompany the intended resistor. Their contribution is not removed by knowing RG's marked value, and a changing connection can introduce changing gain error as well as an initial deviation.
Capacitance at the gain connections raises a different question. The datasheet discusses parasitic capacitance there in relation to stability, and matching the parasitics on the two sides in relation to common-mode rejection over frequency. These are dynamic and balance effects at the gain nodes. A series-resistance error and a capacitive interaction should therefore retain their different mechanisms rather than being combined into one generic parasitic allowance.
The location of the parasitic is essential to this explanation. The gain connections are part of the amplifier's gain-setting network, so their resistance and capacitance act in that context. A source-resistance noise description addresses the signal source, and an output capacitive-load description addresses the driven load. Neither describes the same interface simply because resistance or capacitance appears in all three discussions.
Retain internal-node headroom when changing gain
The INA826 has internal input-stage output nodes as well as its final output. TI identifies their limited swing as an easily overlooked source of overload. Those nodes cannot be measured directly at the device's external output. A requirement based only on the final output voltage can therefore miss a restriction within the earlier stages of the instrumentation-amplifier architecture.
The named example explains the deceptive behavior: one input-stage output can saturate while the other continues responding to input changes. The final output can then appear to move plausibly even though its voltage is invalid. Responsiveness is consequently different from linear operation of all the stages needed for the intended differential transfer. The mechanism concerns an internal headroom condition rather than merely whether the final output has reached a supply rail.
Supply voltage, input common mode, gain and the output-reference context all belong to the permitted operating relationship. TI's low-voltage discussion connects internal swing requirements with common-mode limits, while REF defines the output's reference. Reading those roles together explains why a supply-range match or a plausible output level is insufficient on its own. Changing gain must preserve the internal operating context as well as the desired external transfer.
Sources and further reading
INA826 SBOS562G bounded gain-setting, drift and internal-overload prose on physical pages 18, 20, 21, 23, 24 and 25. No gain equation, parasitic limit, curve value or calibration procedure is supplied.