5-1. Usage considerations for LDO regulators

This section describes the considerations for system design using LDO regulators.

Reverse biasing condition of an LDO regulator (i.e., output voltage higher than input voltage)
If the output voltage of an LDO regulator becomes higher than the input voltage, current flows in the reverse direction from the output pin to the input pin. This reverse biasing condition could degrade or destroy the LDO regulator. If this could occur, connect a bypass diode between the VIN and VOUT pins as shown in Figure 1 or add a reverse-current blocking diode between a power supply and the VIN pin as shown in Figure 2.

When you use a reverse-current blocking diode, exercise care as to a voltage drop due to the diode’s forward voltage (VF) in order to ensure that the LDO regulator operates properly over the input voltage range. A diode with low forward voltage (VF) and leakage current (IR) should be selected, taking the derating of reverse-bias voltage (VR) and forward current (IF) into consideration.

Bypass diode
Diode for reverse-current protection

The following links also provide a description of reverse biasing condition:

Application note: Basics of Low-Dropout (LDO) Regulator ICs

FAQ: Is it OK to reverse-bias an LDO, causing its output voltage to become higher than the input voltage?

Using a ceramic capacitor to smooth the output voltage

Ceramic capacitors are ideal for use with LDO regulators since small ceramic capacitors are becoming available with large capacitance and small equivalent series resistance (ESR). However, the values of ceramic capacitors depend on voltage and temperature as shown below. In particular, the value of the output capacitor greatly affects the negative feedback operation of an LDO regulator. Be sure to fully evaluate a system, taking voltage and temperature into consideration.

Example of a capacitance-vs-voltage curve of a ceramic capacitor
Example of a capacitance-vs-voltage curve of a ceramic capacitor
Example of a capacitance-vs-temperature curve of a ceramic capacitor
Example of a capacitance-vs-temperature curve of a ceramic capacitor

The following links also describe considerations for using a ceramic capacitor to smooth the output voltage:

Application note: Basics of Low-Dropout (LDO) Regulator ICs

Application note: Mechanism of LDO Oscillation and Reducing the Susceptibility to Oscillation

FAQ: What type of capacitor is suitable for use with an LDO regulator?

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Related information

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