Multiplexed Interface Circuit Isolation for SBU-VBUS Short Protection
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Solution Overview
Problem
In mobile devices with multiplexed interfaces, such as USB Type-c interfaces, the pins used for multiplexing functions are adjacent to power input pins, leading to potential short-circuiting and burnout of switch chips when a charging voltage is applied, affecting normal interface use.
Innovation Solution
An interface circuit with a switching unit, resistors, and an on-off apparatus, including NMOS or PMOS transistors, is used to isolate the switching unit during short-circuits, preventing excessive current flow and protecting the switch chip by disconnecting it from ground when a short-circuit occurs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the SBU pin is used for multiplexing function, then the interface can be used as both earphone interface and charging interface, but the SBU pin may be shorted-circuited from the Vbus pin causing burnout of switch chip
Solution Approach 1:
A protection circuit is introduced as an intermediary between the SBU pin and the switch chip. This protection circuit includes a first switch element connected between the SBU pin and the switch chip, and a second switch element connected between the protection circuit and ground. When a short circuit is detected between the SBU pin and Vbus pin, the second switch element is activated to disconnect the protection circuit from ground, thereby isolating the switch chip from the short circuit and preventing burnout while maintaining interface multiplexing functionality
Solution Approach 2:
The protection circuit is designed to preemptively protect the switch chip from potential short circuit damage. By monitoring the voltage level at the SBU pin and automatically activating the second switch element when a short circuit condition is detected (voltage exceeds threshold), the system performs preliminary anti-action to prevent the harmful effect of short circuit current from reaching the switch chip, thus maintaining reliability while preserving multiplexing capability
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 effectively prevents the switch chip from burning out during short-circuits, ensuring normal operation of the interface by limiting current flow through isolation resistors and maintaining functionality during charging and data transmission.
Implementation Method 1
limiting current flow through isolation resistors
Data Source
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AI summary
This application is applicable to the field of terminal technologies, and provides an interface circuit, an interface circuit protection method, and a terminal device. The interface circuit includes: a switching unit, a power input end, a first function pin, a second function pin, a control signal input end, a detection port, a grounding output end, a first resistor, a second resistor, a third resistor, a fourth resistor, and an on-off apparatus. Because the first resistor, the second resistor, the third resistor, and the fourth resistor are respectively connected in series as isolation resistors on their respective paths, when a short circuit occurs, a current flowing through the switching unit is less than a burnout current of the switching unit. In addition, when the switching unit does not work, the grounding output end of the switching unit is suspended by using the on-off apparatus, so that the switching unit is in a suspended state when the switching unit does not work, and is not burned down by a voltage that is input during a short circuit, thereby ensuring normal use of the interface.