The load-step transient response is the output voltage response by the LDO to a step in load current, whereby output voltage regulation is maintained. 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 shown in Figure 8-2 are broken down as follows. Regions A, E, and H are where the output voltage is in steady-state.

Figure 8-2 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 its sourcing current, and leads to output voltage regulation (region C)

• 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 its 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.