USB Charger Detection Circuit with VCCS Voltage Stabilization
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Solution Overview
Problem
Excessive ground plane disturbances interfere with the accurate detection of charger connection status in USB charging systems, leading to incorrect charging status signals and potential failure in fast charging protocols due to voltage fluctuations at the D+ pin.
Innovation Solution
A circuit incorporating a voltage-controlled current source (VCCS) is used to maintain the voltage at the D+ pin within a preselected range by compensating for voltage drops across a resistor, ensuring reliable detection of charger connection through a comparator and switch configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standardized charging protocol is used to ensure proper power navigation, then charging reliability is improved, but the system becomes sensitive to ground plane disturbances that interfere with charger detection
Solution Approach 1:
The patent introduces an intermediary circuit between the USB connector and the detection system that measures voltage at the D+ pin. This intermediary measurement approach isolates the detection system from ground plane disturbances, allowing reliable charger detection despite ground shifts in the charging system.
Solution Approach 2:
The patent replaces direct electrical connection-based detection with voltage measurement-based detection. Instead of relying on direct ground reference for charger detection, the system uses voltage measurements at the D+ pin relative to the local ground, substituting mechanical/electrical direct coupling with an electrical field measurement approach that is immune to ground shifts.
2Measurement precision
If voltage measurement at D+ pin is used for charger detection, then detection accuracy is improved, but ground shifts cause voltage fluctuations that lead to incorrect detection
Solution Approach 1:
The patent implements a feedback mechanism where the voltage at the D+ pin is continuously monitored and compared against threshold values. The system uses this feedback to determine charger presence/absence and to trigger appropriate charging protocols, ensuring accurate detection despite voltage fluctuations from ground shifts.
Solution Approach 2:
The patent changes the detection parameter from direct ground voltage comparison to voltage differential measurement at the D+ pin. By measuring voltage relative to the local ground potential rather than an external reference, the system maintains detection accuracy even when absolute ground potential shifts occur during charging operations.
Data Source
AI summary
A circuit for detecting charger connection through a universal serial bus (UBS) connector is disclosed. The circuit includes a comparator having a first input coupled to a fixed voltage reference and a second input coupled to D+ pin of the USB connector, a voltage controlled current source (VCCS) coupled having a first terminal coupled to a supply and a second terminal coupled to the D+ pin and a resistor coupled between the first terminal and the second terminal of the VCCS. The VCCS is configured to bring voltage at the D+ pin within a preselected voltage range at the D+ pin when the voltage at the D+ pin varies beyond the preselected voltage range.