SBVS311A November 2019 – March 2020 TPS7A54
An low-dropout regulator (LDO) functions as a class-B amplifier, as shown in Figure 40, in which the input signal is the internal reference voltage (VREF). VREF is designed to have very-low bandwidth at the input to the error amplifier through the use of a low-pass filter (VNR/SS).
As such, the reference can be considered as a pure dc input signal. The low output impedance of an LDO comes from the combination of the output capacitor and pass element. The pass element also presents a high input impedance to the source voltage when operating as a current source. A positive LDO can only source current because of the class-B architecture.
This device achieves a maximum of 1% output voltage accuracy primarily because of the high-precision band-gap voltage (VBG) that creates VREF. The low dropout voltage (VDO) reduces the thermal power dissipation required by the device to regulate the output voltage at a given current level, thereby improving system efficiency. These features combine to make this device a good approximation of an ideal voltage source.
NOTE:VOUT = VREF × (1 + R1 / R2).