8.1.3 Load Transient Response

The load-step transient response is the output voltage response by the LDO to a step in load current while output voltage regulation is maintained. See Figure 9, Figure 10, Figure 11, and Figure 12 for typical load transient response. There are two key transitions during a load transient response: the transition from a light to a heavy load, and the transition from a heavy to a light load. The regions in Figure 39 are broken down as described in this section. Regions A, E, and H are where the output voltage is in steady-state operation.

Figure 39. Load Transient Waveform

During transitions from a light load to a heavy load:

• The initial voltage dip is a result of the depletion of the output capacitor charge and parasitic impedance to the output capacitor (region B)
• Recovery from the dip results from the LDO increasing the sourcing current, and leads to output voltage regulation (region C)

During transitions from a heavy load to a light load:

• The initial voltage rise results from the LDO sourcing a large current, and leads to the output capacitor charge to increase (region F)
• Recovery from the rise results from the LDO decreasing the sourcing current in combination with the load discharging the output capacitor (region G)

A larger output capacitance reduces the peaks during a load transient, but slows down the response time of the device. A larger dc load also reduces the peaks because the amplitude of the transition is lowered, and a higher current discharge path is provided for the output capacitor.