LDO Regulator Overcurrent Protection Foldback Mechanism
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Solution Overview
Problem
Conventional low dropout (LDO) regulators face challenges in accurately controlling output current during short circuits or heavy loads due to limited foldback voltage adjustment range and temperature dependencies, leading to potential damage from excessive voltage across components.
Innovation Solution
The implementation of a constant overcurrent limiting circuit and a foldback overcurrent limiting circuit in the LDO regulator, which limits and further decreases the output current when the regulated output voltage falls below a predetermined level, preventing damage by managing output current effectively across the pass transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional over-current protection circuit is used to limit output current during heavy load conditions, then the output current is maintained at a predetermined value, but the foldback voltage is inaccurate and affected by ambient temperature, limiting the adjustment range
Solution Approach 1:
The patent implements a dynamic foldback mechanism where the current limit threshold is not fixed but varies based on the output voltage level. When output voltage drops below a predetermined threshold indicating heavy load or short circuit conditions, the circuit automatically reduces the current limit threshold from a first level to a second level, enabling adaptive protection that responds to changing operating conditions rather than using a static predetermined value
Solution Approach 2:
The patent changes the parameter of current limit threshold dynamically based on output voltage conditions. The circuit monitors output voltage and adjusts the current limit parameter accordingly - maintaining a higher first threshold during normal operation and switching to a lower second threshold during foldback conditions, thereby achieving accurate protection across different operating states without being constrained by temperature-dependent fixed thresholds
2Reliability
If the output current is limited to a predetermined value during short circuit conditions, then protection is provided, but the output current correlates with ambient temperature and process parameters, making control difficult
Solution Approach 1:
The patent employs a feedback mechanism where the circuit continuously monitors the output voltage and uses this information to adjust the current limit threshold. The foldback detection circuit senses when output voltage drops below the predetermined threshold and automatically triggers the threshold switching mechanism, creating a closed-loop control system that compensates for temperature and process variations by responding to actual operating conditions rather than relying on fixed predetermined current values
Solution Approach 2:
The patent implements preliminary protection by establishing a voltage-based trigger mechanism that anticipates dangerous conditions. When output voltage drops below the predetermined threshold, the circuit proactively switches to the lower current threshold before excessive current can cause damage, providing preventive protection that is not dependent on achieving precise current control under varying temperature and process conditions
3Ease of manufacture
If a single over-current protection level is used, then the circuit is simple to implement, but it cannot effectively handle varying load conditions and temperature variations
Solution Approach 1:
The patent implements a dynamic two-level protection system that automatically adapts to different operating conditions. The circuit maintains a first current threshold for normal operation and a second lower threshold for foldback conditions, switching between them based on output voltage monitoring. This dynamic approach provides effective protection across varying load conditions and temperature variations while maintaining relatively simple circuit implementation through the use of voltage-based triggering rather than complex multi-parameter control
Data Source
AI summary
Low dropout regulators capable of preventing damage caused by a short circuit or a heavy load are provided, in which a pass transistor receives an unregulated power supply voltage to generate a regulated output voltage according to a control signal. Additionally, a constant overcurrent limiting circuit limits an output current through the pass transistor to below a predetermined current, and a foldback overcurrent limiting circuit enables the constant overcurrent limiting circuit to further decrease the output current, when the regulated output voltage is lower than a predetermined voltage.