LP38503-ADJ_15 Datasheet, PDF (9/27 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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7 Detailed Description
LP38501-ADJ, LP38503-ADJ
SNVS522I – AUGUST 2007 – REVISED AUGUST 2015
7.1 Overview
The LP38501-ADJ and LP38503-ADJ are FlexCap and low-dropout adjustable regulators, the output voltage can
be set from 0.6 V to 5 V. Standard regulator features, such as overcurrent and overtemperature protections, are
also included.
The LP38501-ADJ and LP38503-ADJ contain several features:
• Stable with any type of output capacitor
• Fast load transient response
• Disable Mode (LP38501-ADJ only)
7.2 Functional Block Diagrams
Figure 11. LP38501-ADJ Block Diagram
Figure 12. LP38503-ADJ Block Diagram
7.3 Feature Description
7.3.1 Stability and Phase Margin
Any regulator which operates using a feedback loop must be compensated in such a way as to ensure adequate
phase margin, which is defined as the difference between the phase shift and –180 degrees at the frequency
where the loop gain crosses unity (0 dB). For most LDO regulators, the ESR of the output capacitor is required to
create a zero to add enough phase lead to ensure stable operation.
Figure 13 shows the gain/phase plot of the LP38501-ADJ and LP38503-ADJ with an output of 1.2 V, a 10-µF
ceramic output capacitor, delivering 2 A of load current. The unity-gain crossover occurs at 300 kHz, and the
phase margin is about 40° (which is very stable).
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