After input settling and soft start time, the TPS2121 utilizes a fast switchover to minimize output voltage drop. Where V_SW is the output voltage when the switchover is triggered and t_SW is the time until the output voltage stops dipping. The amount of voltage dip during the switchover time is a function of output load current (IOUT) and load capacitance (COUT). The minimum output voltage during switchover can be found using the following equations:

Equation 3.

Where:

Equation 4.

Figure 9-7 Minimum Output Voltage During Fast Switchover

If switching from a lower to a higher voltage, the selected channel will not detect reverse voltage and shall turn on immediately using the current monitor to limit the output current to a safe level. If the output current reaches the current limit during fast switchover, this will increase the total time until the output reaches steady state.

Figure 9-8 Fast Switchover from Lower to Higher Voltage

If an input is selected while the output voltage is still a higher voltage, that channel will continue to block reverse current by waiting to fast turn on until the output drops below the V_RCB threshold.

Figure 9-9 Fast Switchover from Higher to Lower Voltage