The simplified CMOS slew boost schematic, Figure 3-2, includes an additional current source that increases the capacitor charge current beyond the bias current level when V_ID becomes large enough. The boost function has a dead band with zero output current while input V_ID is low. At some greater V_ID, the boost current (I_X) rises with the V_ID input. This extra current increases the slew rate considerably. The boost circuit can provide positive and negative current flow to boost both positive and negative slew rates.

Figure 3-2 Simplified CMOS Slew Boost Schematic

The boost current (I_X) versus V_ID can be proportionate or it can be stepped at a certain V_ID level. TLV9001 employs both methods, which is shown in Figure 3-3. Negative SR boost (red) increases proportionately starting near -140mV. Positive slew rate boost (shown in black in Figure 3-3) increases suddenly near +270mV, then raises proportionately. Regardless of the boost type, there is a limit to the boost current output. For very large V_ID, slew rate becomes a fixed value. In the TLV9001 example, the slower SR is about 2V/µs, which matches the data sheet value.

Figure 3-3 TLV9001 Slew Rate With Boost