USB-PD Current Sense Fault Detection Using PWM Correlation
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Solution Overview
Problem
Power converters face reliability issues due to manufacturing defects or malfunctions in the sense resistor, leading to incorrect current sensing and failure to meet safety requirements during output-fault conditions.
Innovation Solution
A secondary-side controller in a USB-PD power converter uses a current sense amplifier and analog-to-digital converter to generate a current code, detecting faults by comparing output current and PWM signal thresholds, enabling dynamic adjustment and disabling the converter if faults persist.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used for current sensing in a USB-PD power converter, then output current measurement is enabled, but manufacturing defects or malfunctions in the sense resistor can lead to incorrect current sensing and safety failures
Solution Approach 1:
The patent implements preliminary fault detection by monitoring the relationship between PWM signal width and sensed current output before actual output-fault conditions occur. The controller proactively identifies potential sense resistor failures by detecting when the sensed current does not appropriately respond to PWM duty cycle changes, enabling preventive safety actions before hazardous conditions develop.
Solution Approach 2:
The patent establishes a feedback mechanism where the controller continuously monitors the correlation between PWM control signals and the resulting current sense amplifier output. By analyzing whether current measurements appropriately track PWM duty cycle variations, the system provides real-time feedback on sense resistor health, allowing dynamic adjustment of safety thresholds or shutdown operations to maintain reliability despite potential sense resistor defects.
2Reliability
If additional fault detection components are added to the power converter, then reliability and safety are improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the existing controller perform multiple functions: it continues to regulate output voltage through PWM control while simultaneously detecting sense resistor faults by analyzing the relationship between PWM width and sensed current. This multi-functionality approach enables fault detection capability without adding dedicated detection hardware, thereby improving reliability while avoiding increased device complexity.
Solution Approach 2:
The system uses its own existing operational signals (PWM control and current sense output) to perform self-diagnosis of sense resistor health. Rather than requiring external test equipment or separate monitoring circuits, the power converter monitors itself during normal operation, detecting when its current sensing subsystem fails to respond appropriately to control inputs, thereby enabling reliability improvement without additional components.
Data Source
AI summary
One or more computing devices, systems, and/or methods are provided. In an example of the techniques presented herein, a method of operating a Universal Serial Bus Power Delivery (USB-PD) power converter is provided. The method includes generating a pulse width modulated (PWM) signal for controlling the power converter. An output current signal for the power converter is determined. The output current signal corresponds to an output current across an external sense resistor coupled in an output path of the USB-PD power converter. A fault condition is identified based on the PWM signal and the output current signal. Operation of the power converter is disabled responsive to identifying the fault condition.