LP38501-ADJ_15 Datasheet, PDF (11/27 Pages) Texas Instruments – LP3850x-ADJ, LP3850xA-ADJ 3-A FlexCap Low Dropout Linear Regulator for 2.7-V to 5.5-V Inputs

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LP38501-ADJ, LP38503-ADJ
SNVS522I – AUGUST 2007 – REVISED AUGUST 2015
Feature Description (continued)
Figure 15 shows the output transient response resulting from a change in load current of 0.1 A – 3 A, and then 3
A – 0.1 A with a load current slew rate of 500 mA/µs. As shown in Figure 15, the resulting change in output
voltage is only about 40 mV (peak), which is just slightly over 2% for the 1.8-V output used for this test. This is
excellent performance for such a small output capacitor.
Figure 15. Load Transient Response: 10-µF Ceramic, 0.5-A/µs Di/Dt
When the load current changes much more quickly, the output voltage will show more change because the loop
and internal feedforward circuitry are not able to react as fast as the load changes. In such cases, it is the output
capacitor which must supply load current during the transition until the loop responds and changes the pass
transistor’s drive to deliver the new value of load current. As an example, the slew rate of the load current will be
increased to 75 A/μs and the same test will be performed. In Figure 16, it can be seen that the peak excursion of
the output voltage during the transient has now increased to about 200 mV, which is just slightly over 11% for the
1.8-V output.
Figure 16. Load Transient Response: 10-μF Ceramic, 75 A/μs di/dt
A better understanding of the load transient can be obtained when the load’s rising edge is expanded in time
scale (Figure 16).
Figure 17. Rising Edge, 10-µF Ceramic, 75 A/µs di/dt
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