USB State Machine Startup via Logic Level Shifting
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Solution Overview
Problem
Existing methods for starting a USB state machine in hand-held terminals fail to provide effective overvoltage protection while sharing a charger and USB communication interface, leading to increased costs and unreliable voltage withstand.
Innovation Solution
A method and terminal that connect the USB voltage bus pin to a logic level, starting both the charging and USB state machines when the charging voltage exceeds a threshold, while shielding USB sessions to prevent overvoltage damage, using a high or low logic level that does not exceed the USB voltage bus pin's withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the VCHG and USB_VBUS are shorted together to share one interface, then the circuit complexity is reduced, but the overvoltage protection capability deteriorates because the USB_VBUS end cannot withstand higher charging voltages
Solution Approach 1:
The patent introduces a level shifting circuit as an intermediary between the charging interface and USB interface. This circuit includes a first level shifting module that converts the charging voltage signal to a USB-compatible signal level, and a second level shifting module that converts USB signals to charging voltage levels. This intermediary structure allows the charging and USB functions to share the same physical interface while maintaining proper voltage levels and overvoltage protection.
Solution Approach 2:
The patent changes the voltage parameter of the USB_VBUS pin by connecting it to a logic level (either high or low) that does not exceed the withstand voltage of the USB voltage bus pin. This parameter change ensures that the USB interface can tolerate charging voltages without being damaged, while still allowing USB communication functionality.
2Reliability
If the VCHG is used to control the USB_VBUS power-on through a hardware circuit, then the overvoltage protection is achieved, but the device complexity increases due to additional external circuits
Solution Approach 1:
The patent implements self-service by using the existing charging voltage detection mechanism to automatically control the USB state machine. When the charging voltage exceeds the threshold, the system automatically starts the charging state machine and USB state machine, and when the voltage drops below the threshold, it automatically quits the USB state machine. This eliminates the need for additional external hardware circuits while maintaining overvoltage protection.
Solution Approach 2:
The patent makes the charging voltage pin serve multiple functions: it detects both charging voltage levels and USB connection status. The same pin and detection mechanism are used to control both charging operations and USB communication, eliminating the need for separate control circuits and reducing overall device complexity.
3Measurement precision
If the USB_VBUS pin is connected to a high logic level to enable USB detection, then the USB detection sensitivity is improved, but the risk of overvoltage damage increases when charging voltage is applied
Solution Approach 1:
The patent applies preliminary action by connecting the USB_VBUS pin to a logic level before USB enumeration begins. This pre-configuration ensures the pin is in a safe state that can detect USB connections without being vulnerable to overvoltage damage from charging operations. The logic level connection is established in advance and maintains protection throughout charging operations.
Data Source
AI summary
A method and terminal for starting a USB state machine are provided in the present document. The method includes: connecting a USB voltage bus pin to a logic level; if detecting that a voltage of a charging voltage pin is greater than a threshold limit value, starting a charging state machine and the USB state machine. In the present document, the USB state machine is started through a signal for detecting plug-in and pull-out of a charger, which can not only trigger the start-up of the USB state machine, but also possess a function of satisfying overvoltage protection, thereby the charger and the USB are enabled to share one physical interface with the simplest and securest method under the premise of guaranteeing the reliability.