LDO Regulator Startup Control with Delayed Foldback Protection
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Solution Overview
Problem
Existing low dropout linear regulators face issues with normal startup during power-on due to maloperations of foldback current-limiting protection and undershoot suppression circuits, leading to incorrect current limiting and overshoot/undershoot events, which can cause chip heating and safety hazards.
Innovation Solution
A control circuit for a low dropout linear voltage regulator comprising an error amplifier, foldback current-limiting protection circuit, undershoot suppression circuit, and output detection circuit, where the output detection circuit disables the foldback and undershoot suppression circuits before the output voltage reaches a preset value, ensuring proper startup and preventing maloperations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If foldback current-limiting protection circuit and undershoot suppression circuit are enabled during startup, then current protection and voltage stability are improved, but the circuits cause maloperation and prevent normal startup
Solution Approach 1:
The output detection circuit detects the output voltage before the foldback current-limiting protection circuit and undershoot suppression circuit are enabled. When the output voltage reaches a preset threshold, it signals that startup is complete, allowing the protection circuits to be safely enabled afterward. This preliminary detection action prevents maloperation during startup while maintaining protection functionality during normal operation.
2Object-affected harmful factors
If foldback current-limiting protection is activated during startup, then short circuit protection is improved, but output voltage cannot reach preset value and startup fails
Solution Approach 1:
The output detection circuit performs preliminary detection of the output voltage before enabling the foldback current-limiting protection circuit. Only when the output voltage reaches the preset threshold does the detection circuit enable the protection circuit, ensuring that voltage precision requirements are met before current limiting is activated, thus preventing startup failure.
3Stability of the object's composition
If undershoot suppression circuit is enabled during startup, then voltage fluctuation suppression is improved, but circuit maloperation occurs preventing normal startup
Solution Approach 1:
The output detection circuit detects whether the output voltage has reached the preset threshold before enabling the undershoot suppression circuit. This preliminary action ensures that the suppression circuit is only activated when startup is complete, preventing maloperation during the critical startup phase while maintaining voltage fluctuation suppression during normal operation.
Data Source
AI summary
Disclosed is a low dropout linear voltage regulator and a control circuit thereof. The control circuit comprises an error amplifier, a foldback current-limiting protection circuit, an undershoot suppression circuit and an output detection circuit. The foldback current-limiting protection circuit limits the output current of power transistor and performs short circuit protection, the undershoot suppression circuit pulls the control terminal of the power transistor to low voltage level when the output voltage undershoots. The output detection circuit judges whether the output voltage rises to a preset voltage value in the startup stage, and before the output voltage rises to the preset voltage value, disables the undershoot suppression circuit and the foldback characteristic of the foldback current-limiting protection circuit, which can prevent normal startup of the circuit from being affected by a maloperation of the foldback current-limiting protection circuit and the undershoot suppression circuit during the startup process, improve on-load startup ability.