Application note regarding proper usage of LDO from Analog Devices. Link here (PDF)
A low dropout (LDO) regulator is capable of maintaining its specified output voltage over a wide range of load currents and input voltages, down to a very small difference between input and output voltages. This difference, known as the dropout voltage or headroom requirement, can be as low as 80 mV at 2 A.
Current portable devices often require up to 20 low dropout linear regulators. Many of the LDOs in today’s portable devices are integrated into multifunction power management ICs (PMICs), highly integrated systems with many power domains for audio, battery charging, housekeeping, lighting, communications, and other functions.
As portable systems rapidly evolve, however, the integrated PMIC cannot keep up with peripheral power requirements. Dedicated LDOs must be added in the later stages of system development to power such optional items as camera modules, Bluetooth®, WiFi®, and other bolt-on functions. LDOs have also been used to reduce noise, to solve voltage-regulation problems caused by electromagnetic interference (EMI) and printed circuit board (PCB) routing, and to improve system power efficiency by switching off unneeded functions.
This application note reviews the basic LDO topology, explains key specifications, and shows the application of low dropout voltage regulators in systems.