A low drop-out voltage regulator is a regulator circuit that provides a well-specified and stable DC voltage (whose input-to-output voltage difference is typically low). The operation of the circuit is based on feeding back an amplified error signal which is used to control output current flow of a pass device (such as a power transistor) driving a load. The drop-out voltage is the value of the input/output differential voltage where regulation is lost.
The low drop-out nature of the regulator makes it appropriate (over other types of regulators such as dc-dc converters and switching regulators) for use in many applications such as automotive, portable, and industrial applications. In the automotive industry, the low drop-out voltage is necessary during cold-crank conditions where an automobile's battery voltage can be below 6V. Increasing demand for LDO voltage regulators is also apparent in mobile battery operated products (such as cellular phones, pagers, camera recorders and laptop computers), where the LDO voltage regulator typically needs to regulate under low voltage conditions with a reduced voltage drop.
A typical, known LDO voltage regulator uses a differential transistor pair, an intermediate-stage transistor, and a pass device coupled to a large (external) bypass capacitor. These elements constitute a DC regulation loop which provides voltage regulation.
Depending on the application, a critical component of the regulator is often its bypass capacitor. Indeed, to ensure stability under all operating conditions, large values of capacitor are used. This translates into large area on the PCB on which the regulator circuit is built, and higher costs.
However, this known LDO voltage regulator has the disadvantages that it is difficult (i) to significantly reduce the bypass-capacitor below approximately 1 μF per 10 mA output current capability, and (ii) to significantly increase the PSRR frequency behavior without high increase of power consumption.
A need therefore exists for a low drop-out voltage regulator wherein the abovementioned disadvantage(s) may be alleviated.