Low-Dropout Regulator Startup Switching to Prevent Voltage Overshoot
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Solution Overview
Problem
Conventional low dropout linear regulators experience overshoot during startup due to instantaneous changes in output current, leading to potential functional failures and overheating in connected load circuits, as they struggle to smoothly reach target voltage values.
Innovation Solution
Implementing a switch circuit to automatically switch between current feedback and voltage feedback loops, with different voltage references at various stages of the startup process, limiting output current magnitude and preventing overshoot by transitioning from current feedback to voltage feedback mode when the output voltage approaches the target value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LDO uses a conventional voltage feedback loop during startup, then the output voltage can reach the target value, but the output current cannot quickly drop causing voltage overshoot that may damage load circuits
Solution Approach 1:
The feedback control is segmented into two distinct modes: current feedback mode for startup phase and voltage feedback mode for steady-state operation. The switching circuit selects which feedback mode to use based on the operational phase, allowing optimized control for each phase without compromise
Solution Approach 2:
The current feedback mode is activated preliminarily during startup to preemptively control the output current waveform. By shaping the current in advance during charging, the system prevents the current from being too high when voltage feedback takes over, avoiding overshoot before it occurs
2Reliability
If the LDO limits output current during startup to prevent overshoot, then load circuit safety is improved, but the output voltage rises slowly affecting startup speed
Solution Approach 1:
The control strategy is applied periodically in two distinct phases: first current feedback for startup, then voltage feedback for steady-state. This periodic switching allows the system to benefit from current limiting during charging while achieving fast voltage response during regulation
Solution Approach 2:
The feedback parameter is dynamically changed from current feedback to voltage feedback based on operational phase. During startup, current feedback shapes the current waveform; during steady-state, voltage feedback provides fast response, optimizing both safety and speed
3Productivity
If the LDO uses high output current for fast startup, then productivity is improved, but the output voltage overshoots causing functional failure in load circuits
Solution Approach 1:
The system uses feedback control in two forms: current feedback during startup to monitor and limit output current, and voltage feedback during steady-state to maintain precise voltage regulation. The switching circuit transitions between these feedback mechanisms based on operational phase
Solution Approach 2:
Current feedback is applied preliminarily during startup to preemptively control the output current waveform. By limiting and shaping the current in advance, the system prevents the current from being too high when voltage feedback takes over, avoiding overshoot before it occurs
Data Source
AI summary
Disclosed is a low dropout linear regulator and a voltage stabilizing method therefor in embodiments. The low dropout linear regulator includes: a drive circuit, generating a first control signal according to a voltage reference and a feedback voltage and generating an output current according to the first control signal, a load capacitor providing an output voltage according to the output current; a voltage feedback circuit, obtaining the feedback voltage according to the output voltage; a current feedback circuit, generating a second control signal according to the output current; a switch circuit, providing the voltage reference according to the second control signal. Among them, in a first phase of a startup process, the voltage reference is less than or equal to an initial value, and the current feedback circuit limits the output current according to the second control signal; in a second phase of the startup process, the switch circuit switches a voltage value of the voltage reference to a target value. The low dropout linear regulator and the voltage stabilizing method therefor of the embodiment of the disclosure, during the startup process, may effectively limit the output current and make the output voltage rise gently so as to reduce or avoid overshoot.