LDO Low Dropout Linear Regulator

LDO is a micro-power low-dropout linear regulator that usually has extremely low self-noise and high power supply rejection ratio PSRR (Power Supply Rejection Ratio).

LDO is a new generation of integrated circuit voltage regulator. The biggest difference between it and the three-terminal voltage regulator is that LDO is a micro system on chip (SoC) with very low self-consumption. It can be used for current main channel control. The chip integrates MOSFET with extremely low online on-resistance, Schottky diode, sampling resistor and voltage divider resistor and other hardware circuits, and has over-current protection, over-temperature protection, precision reference source, differential amplifier, delayer and other functions. PG is a new generation of LDO, with self-checking of each output state and delayed safe power supply function, which can also be called Power Good, that is, "good power or stable power supply".

The structure of the LDO low-dropout linear regulator mainly includes a startup circuit, a constant current source bias unit, an enable circuit, an adjustment element, a reference source, an error amplifier, a feedback resistor network, and a protection circuit. The basic working principle is as follows: when the system is powered on, if the enable pin is at a high level, the circuit starts to start, the constant current source circuit provides bias to the entire circuit, the reference source voltage is quickly established, and the output continues to rise with the input. When the output is about to reach the specified value, the output feedback voltage obtained by the feedback network is also close to the reference voltage value. At this time, the error amplifier amplifies the small error signal between the output feedback voltage and the reference voltage, and then amplifies it to the output through the adjustment tube, thereby forming a negative feedback, which ensures that the output voltage is stable at the specified value. Similarly, if the input voltage changes or the output current changes, this closed loop will keep the output voltage unchanged, that is: Vout=(R1+R2)/R2 ×Vref

The actual low dropout linear regulator also has other functions such as load short circuit protection, overvoltage shutdown, overtemperature shutdown, reverse connection protection, etc.