What are typical applications for a low dropout (LDO) linear regulator?

LDO linear regulators are usually employed in systems that require a low-noise power source instead of a switching regulator that might upset the system. LDOs also find use in applications where the regulator must maintain regulation with small differences between the input supply voltage and output load voltage, such as battery-powered systems. Their low dropout voltage and low quiescent current make them a good fit for portable and wireless applications.

 

How much output current can an LDO provide?

LDOs with an on-chip power MOSFET or bipolar transistor typically provide outputs in the 50 mA to 1 A range. Some newer circuits can actually handle higher currents.

What is a typical LDO regulator circuit?

An LDO voltage regulator operates in the linear region with the topology shown in the Figure. As a basic voltage regulator its main components are a series pass transistor (bipolar transistor or MOSFET), differential error amplifier, and precise voltage reference.

LDO voltage regulator employs a series pass transistor (bipolar transistor or MOSFET), differential error amplifier, and precise voltage reference.

One input to the differential error amplifier, set by resistors R1 and R2, monitors a percentage of the output voltage. The other error amplifier input is a stable voltage reference (VREF). If the output voltage increases relative to VREF, the differential error amplifier changes the pass-transistor's output to maintain a constant output load voltage (VOUT).  The enable EN input is used to sequence multiple LDOs and/or place the LDO input an ultra-low power dissipation state.