PFM Switching Converter Control Using Minimum Off-Time Fault Sensing
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Solution Overview
Problem
Existing PFM regulation loops in switching converters, particularly in low-consumption applications, lack effective methods for monitoring load current and detecting anomalous events like overcurrent or short circuits without increasing static current consumption or area occupation.
Innovation Solution
Implement a system and method in the control unit of a switching converter that utilizes the PFM regulation loop to monitor current by defining a minimum duration for the off-time interval, enabling overcurrent detection and protection through a PFM logic stage with a second definition stage and detection stage, which includes an AND gate, flip-flop, NOR gate, and counter to detect anomalous events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional circuit stages are implemented to detect overcurrent faults in a voltage control regulation loop, then overcurrent detection capability is improved, but static current consumption and area occupation increase
Solution Approach 1:
The system uses its own existing operational parameters (switching frequency, on-time duration) to detect overcurrent conditions. The control unit monitors whether the actual switching frequency exceeds a threshold value or whether the on-time duration becomes abnormally short, which indicates overcurrent. This self-monitoring approach eliminates the need for separate detection circuits, thereby avoiding additional static current consumption and area occupation while maintaining reliable overcurrent protection
Solution Approach 2:
The control unit is designed to perform multiple functions: it simultaneously controls the switching operation, regulates the output voltage, and detects overcurrent conditions. By integrating overcurrent detection into the existing control unit's functionality rather than adding separate dedicated detection circuitry, the system achieves multi-functionality without increasing static current consumption or area occupation
2Reliability
If additional circuit stages are implemented to detect overcurrent faults in a voltage control regulation loop, then overcurrent detection capability is improved, but area occupation increases
Solution Approach 1:
The system uses its own existing operational parameters (switching frequency, on-time duration) to detect overcurrent conditions. The control unit monitors whether the actual switching frequency exceeds a threshold value or whether the on-time duration becomes abnormally short, which indicates overcurrent. This self-monitoring approach eliminates the need for separate detection circuits, thereby avoiding additional area occupation while maintaining reliable overcurrent protection
Solution Approach 2:
The control unit is designed to perform multiple functions: it simultaneously controls the switching operation, regulates the output voltage, and detects overcurrent conditions. By integrating overcurrent detection into the existing control unit's functionality rather than adding separate dedicated detection circuitry, the system achieves multi-functionality without increasing area occupation
3Use of energy by moving object
If PFM regulation loop is used to reduce energy consumption, then static current consumption is reduced, but ability to monitor load current and detect anomalous events is lost
Solution Approach 1:
The PFM control unit monitors its own operational parameters (switching frequency, on-time duration) to detect overcurrent conditions. By using self-monitoring of existing operational characteristics rather than external sensing circuits, the system maintains load current monitoring capability in low-power PFM mode without incurring additional static current consumption
Solution Approach 2:
The system implements feedback by monitoring the relationship between switching frequency and on-time duration. When the switching frequency exceeds a threshold or the on-time becomes abnormally short, this feedback indicates an overcurrent condition. This feedback mechanism enables continuous load current monitoring without requiring additional power-consuming circuitry
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A control unit (2) is described, for controlling a converter (1) with PFM-regulated switching operation, configured to generate a control signal (Sc) of the square wave type to control switching of at least one switch element (4) of the converter, having a switching period where a first time interval (Ton) and a second time interval (Toff) are defined, associated with a respective value, that is high or low, of the control signal (Sc); wherein the control unit (2) determines a constant duration of the first time interval (Ton) and also a minimum duration (Toff_min) of the second time interval (Toff), in such a way as to determine a maximum operating frequency of the converter (1). The control unit implements a detection stage (26), for detecting an anomalous current event, as a function of a count of a predetermined number (N) of temporally successive periods of the control signal (Sc) during which the converter (1) operates with said minimum duration (Toff_min) for the second time interval (Toff) and, consequently, with the maximum operating frequency.