What is a Quasi-LDO?
A Quasi-LDO is a type of linear regulator. A linear regulator uses a transistor or FET, operating in its linear region, to subtract excess voltage from the applied input voltage, producing a regulated output voltage. Dropout voltage is the minimum input to output voltage differential required for the regulator to sustain an output voltage within 100mV of its nominal value. Quasi-LDO (Low Drop-Out) regulators often use an NPN power transistor as the pass device, driven by a PNP. The dropout voltage for a Quasi-LDO is Vsat (PNP) + Vbe (NPN), typically around 1V total. This value is between the LDO typical dropout of 200mV and the traditional linear regulator dropout of about 2V. National”s QLDO products include the LM3480 and LM3490, for load currents of up to 0.1A, and the LM1117, LM1084, LM1085, and LM1086 for load currents of 0.8A – 5A. The LM3480 and LM3490 are supported by National”s Power WEBENCH online design environment.
