| Low Dropout Regulator |
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Regulation A regulator's dropout voltage determines the lowest usable supply voltage. If, for example, theLDO has a dropout voltage around 700mV (0.7V), a 3.3V output would require the input to be at least 4V. Thus the LDO may be specified to provide a fixed 3.3V output with a 4V to 5.5V input. An LDO's output voltage variation is due primarily to a variation in the Temperature of the constant voltage reference source and the Differential Amplifier characteristics, as well as the sampling resistor tolerance (R1 and R2). Some LDOs employ a control or bias voltage that provides the ability to supply lower output voltages. Quiescent Current Among other important characteristics is the quiescent, or ground current (the current flowing through the system when no load is present), which creates a difference between the input and output currents. The series pass element, Topologies , and ambient temperature are the primary contributors to quiescent current. Quiescent current and input/output limit the efficiency of LDO regulators and should thus be minimized. |
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