P-Channel LDO Regulator Feedback for Stable Dominant Pole Control
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Solution Overview
Problem
Low dropout (LDO) voltage regulators using p-channel MOSFET transistors face high impedance at the output node and a dominant pole that is externally affected by load capacitance and resistance, leading to stability and transient response issues.
Innovation Solution
Incorporating first and second feedback circuits with a p-channel transistor pass device, where the second feedback circuit acts as a buffer and reduces impedance, and a circuit configuration that internalizes the dominant pole, enhancing stability and transient response by adjusting the voltage and current dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a p-channel transistor is used as the pass device in an LDO voltage regulator, then the regulator can achieve lower power operation, but the output impedance becomes high and stability deteriorates
Solution Approach 1:
The patent implements a feedback circuit that senses the output voltage and adjusts the gate voltage of the p-channel pass device accordingly. This feedback mechanism compensates for the high output impedance characteristic of p-channel transistors, maintaining stable output voltage despite load variations, thereby resolving the stability deterioration while preserving low power operation
Solution Approach 2:
The patent dynamically adjusts the gate-source voltage of the p-channel pass device based on load conditions and output voltage requirements. By changing the operating parameters (voltage levels) of the p-channel transistor, the circuit optimizes both power consumption and output impedance characteristics, achieving stability without sacrificing the low power advantage
2Use of energy by moving object
If a p-channel transistor is used as the pass device, then power operation is reduced, but the dominant pole becomes externally affected by load capacitance and resistance
Solution Approach 1:
The patent introduces an intermediate compensation circuit between the feedback network and the pass device gate. This intermediary circuit isolates the dominant pole from external load variations by providing a buffered control voltage, thereby reducing sensitivity to load capacitance and resistance while maintaining the low power operation benefits of the p-channel transistor
3Area of stationary object
If traditional LDO voltage regulator configuration is used with p-channel transistor, then area and costs are reduced, but transient response becomes poor
Solution Approach 1:
The patent implements dynamic control of the pass device gate voltage with enhanced bandwidth compensation. The compensation circuit responds rapidly to load transients, dynamically adjusting the gate voltage to maintain output stability during transient events, thereby improving transient response without increasing chip area or cost
Data Source
AI summary
A voltage regulator may comprise an output node, a pass device, a first feedback circuit, and a second feedback circuit. The output node may be operable to be coupled to a load. The pass device may be operable to pass current to the output node based on a voltage applied to the pass device, wherein the pass device comprises a p-channel transistor. The first feedback circuit may be operable to adjust the voltage applied to the pass device based on an output node voltage. The second feedback circuit may be operable to adjust the voltage applied to the pass device based on a change to the output node voltage.