LDO Regulator Stability via Replica Device Feedback
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Solution Overview
Problem
Low-dropout LDO regulators face stability issues due to parasitic inductance in external wiring, leading to undesirable oscillations and reduced stability of the feedback control loop, especially when the input voltage is close to the target output voltage, requiring large decoupling capacitors to maintain regulation.
Innovation Solution
A power converter design with a pass device and a replica device, where the feedback circuit generates a control signal to regulate both devices, and a regulation circuit reduces the voltage difference between the coupling voltage and the output voltage, allowing for smaller decoupling capacitors and increased stability, using a metal-oxide-semiconductor field-effect transistor (MOSFET) and a voltage-controlled current source to equalize voltages across the devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large decoupling capacitor is used at the input of the LDO regulator, then the stability of the feedback control loop is improved, but the device complexity and component size increase
Solution Approach 1:
The patent introduces a replica device as an intermediary element that mirrors the electrical characteristics of the pass device. This replica device, coupled with a regulation circuit, acts as a mediator to compensate for the destabilizing effects of parasitic inductance without requiring large decoupling capacitors. The replica device generates compensating signals that counteract the oscillations caused by external wiring inductance.
Solution Approach 2:
The regulation circuit dynamically adjusts the coupling voltage based on the operating conditions of the LDO regulator. By changing the voltage parameter at the coupling node, the system optimizes the feedback loop stability across different load and voltage conditions, eliminating the need for fixed large decoupling capacitors.
2Use of energy by moving object
If the input voltage is close to the output voltage, then power consumption is reduced, but the stability of the feedback control loop deteriorates due to reduced current difference between pass and replica devices
Solution Approach 1:
The regulation circuit continuously monitors the coupling voltage and adjusts it based on feedback from the feedback control loop. This feedback mechanism ensures that the replica device maintains appropriate current characteristics even when the input-output voltage difference is small, preserving loop stability while allowing low-power operation.
Solution Approach 2:
The system proactively compensates for potential stability issues by using the regulation circuit to pre-adjust the coupling voltage before instability occurs. This preliminary anti-action prevents the feedback loop from becoming unstable when operating at low voltage differences, avoiding oscillations before they can develop.
3Adaptability or versatility
If parasitic inductance in external wiring is present, then the LDO regulator can be implemented with standard wiring, but undesirable oscillations occur that disturb the feedback control loop
Solution Approach 1:
The patent converts the harmful effect of parasitic inductance into a beneficial compensation mechanism. The replica device, which experiences similar parasitic inductance effects, generates compensating signals that counteract the oscillations. By mirroring and inverting the harmful effect, the system eliminates oscillations while maintaining compatibility with standard external wiring.
Data Source
AI summary
A power converter and method are presented. The power converter may have a pass device, a replica device, a feedback circuit, and a regulation circuit. The pass device may be coupled on a first electrical path between an input terminal of the power converter and an output terminal of the power converter. The replica device may be coupled on a second electrical path between the input terminal and the output terminal, wherein a coupling node is arranged on the second electrical path between the replica device and the output terminal. The feedback circuit may generate, based on a reference voltage and an output voltage at the output terminal, a control signal for controlling both the pass device and the replica device. The regulation circuit may reduce a voltage difference between a coupling voltage at the coupling node and the output voltage at the output terminal of the power converter.