Ground Plane Isolation Circuit for Automotive USB Protection
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Solution Overview
Problem
In automotive environments, existing solutions fail to effectively protect multiple USB ports and associated components from high voltage exposure, leading to potential damage and safety hazards due to electromagnetic interference and electrostatic discharges, as conventional methods like MOSFET isolation are either ineffective or cost-prohibitive.
Innovation Solution
A protection circuit system utilizing NMOS and PMOS transistors with shunt resistors and transient voltage suppressing diodes, coupled with operational amplifiers and OR circuits, isolates individual ground connections from a common ground, allowing for smart transient voltage suppression and current limiting, thereby preventing excessive voltage exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single MOSFET isolation scheme is used to isolate the entire module from ground, then the cost is reduced, but the protection effectiveness deteriorates due to interaction and interconnection of functional sections
Solution Approach 1:
The patent divides the single ground isolation into multiple segmented isolation circuits, each protecting a specific functional section (DC-DC converter, USB HUB, etc.). Each section has its own MOSFET and control circuit, allowing independent protection without interfering with other sections. This segmentation resolves the contradiction by maintaining cost-effectiveness while improving protection reliability through localized isolation.
2Reliability
If multiple isolation circuits are implemented for each USB port connection line, then the protection effectiveness is improved, but the device complexity and cost increase significantly
Solution Approach 1:
The patent merges the isolation control for multiple connection lines (Vbus, Gnd, D+, D-) into a single control mechanism per functional section. Instead of isolating each line independently, the ground connection is isolated for the entire section, providing protection for all lines simultaneously. This merging approach maintains high protection effectiveness while significantly reducing circuit complexity and component count.
3Reliability
If the entire board ground is isolated through a MOSFET switch, then the protection coverage is maximized, but the system functionality deteriorates due to ground potential differences between functional sections
Solution Approach 1:
The patent implements segmented ground isolation where each functional section (DC-DC converter, USB HUB, etc.) has its own ground isolation circuit. This allows each section to be isolated independently when needed, maintaining protection coverage while preserving the ground reference for non-isolated sections. The segmentation enables selective isolation that maintains system functionality by preventing ground potential differences across the entire board.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides economical and effective protection against high voltage exposure, preventing damage and ensuring system integrity by maintaining ground potential below 5V during isolation, allowing the module to function normally after exposure to high voltages without causing fires or smoke.
Implementation Method 1
an NMOS transistor having a load path connecting a common ground connection with an individual ground connection of the integrated circuit device, and having a gate connection receiving an activation signal
Implementation Method 2
a first shunt resistor coupled in parallel with the load path
Implementation Method 3
a transient voltage suppressing device coupling the load path with the individual ground connection
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A system has a plurality of circuits (210, 220, 230) each having an individual ground connection ("Old" HUB GND). The system further has a common ground connection (Chassis GND) connected with each ground connection of each circuit of the plurality of circuits via an associated isolation circuit (310), wherein each isolation circuit has: an NMOS transistor (Q101) having a load path connecting the common ground connection with an individual ground connection of an associated circuit, and having a gate connection receiving an activation signal (ACC), and a first shunt resistor (R103) coupled in parallel with the load path.