LDO Minimum Output

Formula

Description

A low-dropout regulator (LDO) requires a minimum voltage difference between input and output to maintain regulation. The dropout voltage is the minimum Vin - Vout at which the regulator can still maintain its specified output voltage accuracy. Modern LDOs achieve dropout voltages as low as 30-200 mV at full load, compared to 1-2V for traditional linear regulators. Dropout voltage typically increases with load current. When Vin drops below Vout + Vdropout, the LDO enters dropout and the output follows the input minus a small saturation voltage.

Variables

• Vout_min — Minimum regulated output voltage (V)
• Vin — Input supply voltage (V)
• Vdrop — Dropout voltage (V)

Practical Notes

LDO dropout voltage is specified at a particular load current and temperature. At light loads, dropout can be much lower. PMOS-based LDOs have lower dropout than NPN-based regulators. For battery-powered devices, low dropout is critical to extract maximum energy from the battery before the terminal voltage drops too low.