LP38501TS-ADJ Datasheet, PDF (11/22 Pages) Texas Instruments – LP38501/3-ADJ, LP38501A/3A-ADJ 3A FlexCap Low Dropout Linear Regulator for 2.7V to 5.5V Inputs

LP38501-ADJ, LP38503-ADJ
www.ti.com
SNVS522H – AUGUST 2007 – REVISED APRIL 2013
As a first example, larger values of ceramic capacitance will be tried to show how much reduction can be
obtained from the 200 mV output change (Figure 20) which was seen with only a 10 µF ceramic output capacitor.
In Figure 21, the 10 µF output capacitor is increased to 22 µF. The 200 mV transient is reduced to about 160
mV, which is from about 11% of V_OUT down to about 9%.
Figure 21. 22 µF Ceramic Output Capacitor
In Figure 22, the output capacitance is increased to 47 µF ceramic. It can be seen that the output transient is
further reduced down to about 120 mV, which is still about 6.6% of the output voltage. This shows that a 5X
increase in ceramic capacitance from the original 10 µF only reduced the peak voltage transient amplitude by
about 40%.
Figure 22. 47 µF Ceramic Output Capacitor
In general, managing load transients is done by paralleling ceramic capacitance with a larger bulk capacitance.
In this way, the ceramic can source current during the rapidly changing edge and the bulk capacitor can support
the load current after the first initial spike in current.
In the next test, the same 10 µF ceramic capacitor will be paralleled with a general purpose (cheap) aluminum
electrolytic whose capacitance is 220 µF. As shown in Figure 23, there is a small improvement over the 200 mV
peak seen with the 10 µF ceramic alone. By adding the 220 µF aluminum capacitor, the peak is reduced to about
160 mV (the same peak value as seen with a 22 µF ceramic capacitor alone).
Figure 23. 10 µF Ceramic Paralleled By 220 µF Generic Aluminum Electrolytic
Copyright © 2007–2013, Texas Instruments Incorporated
Submit Documentation Feedback
11
Product Folder Links: LP38501-ADJ LP38503-ADJ