Self-adapting Voltage Amplifier for USB Charger Detection
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Solution Overview
Problem
Conventional voltage followers in portable devices cannot meet the USB battery charging specification revision 1.2 requirements for maintaining a D+ pin voltage above 2.2V when a pull-up resistor is present, due to negative feedback circuit limitations.
Innovation Solution
A self-adapting amplifier with variable and fixed bias circuits that adjust transconductance in response to external connection conditions, allowing the D+ pin voltage to rise above 2.2V by reducing transconductance and increasing output voltage when a pull-up resistor is connected, while maintaining 0.5-0.7V voltage during charger detection without a resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional voltage follower operational amplifier is used to maintain D+ pin voltage during charger detection, then the voltage can be maintained at 0.5-0.7V while sourcing at least 250 μA current, but the voltage cannot rise above 2.2V when a pull-up resistor is present due to negative feedback circuit limitations
Solution Approach 1:
The amplifier circuit dynamically adjusts its transconductance based on external connection conditions. When a pull-up resistor is detected, the transconductance is reduced to allow the output voltage to rise above 2.2V. When no pull-up resistor is present, the transconductance is increased to maintain the voltage at 0.5-0.7V during charger detection. This dynamic adaptation enables compliance with USB battery charging specification revision 1.2 while maintaining proper operation in both configurations.
Solution Approach 2:
The invention changes the transconductance parameter of the amplifier based on the detected external conditions. By varying the transconductance, the amplifier can switch between two operating modes: one for charger detection (maintaining 0.5-0.7V) and another for ACA-Dock detection (allowing voltage to rise above 2.2V). This parameter change resolves the contradiction by making the amplifier's behavior conditional rather than fixed.
2Adaptability or versatility
If the amplifier maintains low transconductance to allow voltage rise above 2.2V with pull-up resistor, then compliance with revision 1.2 is achieved, but the ability to maintain 0.5-0.7V during charger detection without pull-up resistor is compromised
Solution Approach 1:
The amplifier circuit incorporates feedback mechanisms that monitor the external connection conditions at the output terminal. Based on this feedback, the circuit automatically adjusts its transconductance to the appropriate level. This feedback-based control ensures that the amplifier maintains the correct voltage level for charger detection when no pull-up resistor is present, while allowing the voltage to rise above 2.2V when a pull-up resistor is detected, thus maintaining both reliability and adaptability.
Solution Approach 2:
The amplifier circuit is designed to perform multiple functions: it can maintain low voltage (0.5-0.7V) during charger detection and allow high voltage (>2.2V) during ACA-Dock detection. By making the amplifier universal and capable of operating in both modes, the invention resolves the contradiction between charger detection accuracy and voltage adaptability, as the same circuit reliably performs both functions based on the detected configuration.
Data Source
AI summary
An amplifier applies a self-adapting voltage to an output terminal. A bias circuit provides a greater bias current in a first external connection condition, in the absence of a pull-up resistance connected to the output terminal, than when such a pull-up resistance is present. The amplifier applies a different voltage to the output terminal in the absence of a pull-up resistance than when such a pull-up resistance is present. The circuit can be used in a portable device for receiving charging current from a battery charger through a connector having a D+ pin for connection to the battery charger and connected to the amplifier output terminal for battery charger detection. The portable device can meet the USB battery charger specification rev. 1.2.