One simplified view of a voltage feedback amplifier is as a transistor differential pair, current mirror, and output buffer stage, shown in Figure 1-1. The inputs of the opamp, IN+ and IN-, are inputs to the differential pair. The voltage at the inputs directly determine the current across the legs of the pair, I1 and I2. A current mirror at the bottom of the pair forces a difference current, I2 - I1, to flow out of the right leg. If the input voltages are perfectly matched, this current will be zero. However, if an input step is applied, it drives the inputs, and therefore the currents, apart. The difference current goes into a buffer stage and charges the compensation capacitor, CC. A capacitor's voltage change rate is known, and this gives us our overall slew rate: v/dt = (I1 - I2)/CC. This shows that slew rate has a direct relation to the differential input voltage (V_ID).

Because of the fixed tail current source, I1 and I2 can go up to the current source value, B. This sets the maximum slew rate values to -B/CC to +B/CC. This can be a significant limitation, since the tail current source is kept small for other design reasons. From this description it is easy to see why high gain applications result in low slew rates. In high gain, the input differential voltage is very small and there is not enough difference to allow the differential pair to output the maximum current.

To improve slew rate performance, some amplifiers include slew-boost circuitry that provides another current source to add supplement current to charge the capacitor faster. Slew boost circuitry may or may not be dependent on the input differential voltage depending on the type of design. There are many good sources for further explanation of voltage feedback slew rate and slew boost, one of which is Ramping Up on Slew Rate. A link to this and other resources can be found in the references section.