New error amplifier topology for Low Dropout Voltage regulators using compound OTA-OPAMP
Typical Low Dropout Voltage regulators (LDO), uses an error amplifier in a linear closed loop. The main advantage of such linear regulators is the low standby current due to the absence of switching. In addition, a fully integrated linear regulator with no external components is very attractive for applications with stringent area, low weight requirements and relatively small peak power. The architecture of error amplifier used in the feedback loop suffers from an inherent load regulation performance limitation. This limitation manifests itself through the limited DC open-loop gain, and results from limited closed-loop bandwidth. The frequency response of power supply loop is highly sensitive to the load conditions, thus, making proper compensation is a laborious effort. This paper discusses and addresses a new topology of an error amplifier offering a high open loop gain as well as a large band width by adding a zero to its transfer function. Proposed topology uses a compound OTA and OPAMP that enhances load regulation performance by relaxing the dc open-loop gain restrictions. An example of battery charger using this OpAmp topology is also described in this paper. This battery charger can be used as an LDO once the battery is not connected.