USB Microcontroller for Handheld Device Enumeration
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Solution Overview
Problem
Handheld devices requiring greater than 100 mA to enumerate their main processor face challenges with USB Specification Revision 2.0, which limits current draw to 100 mA before enumeration, potentially preventing sufficient power for chipset startup and enumeration.
Innovation Solution
Incorporating a USB microcontroller or USB hub controller that can perform enumeration with less than 100 mA, allowing the device to draw up to 500 mA post-enumeration, and utilizing a rechargeable battery with a power management IC to manage power levels and initiate enumeration when the battery is low.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the handheld device draws more than 100 mA during enumeration, then the main processor can be properly powered and enumerated, but the USB Specification Revision 2.0 limit of 100 mA prevents sufficient power for chipset startup
Solution Approach 1:
A USB microcontroller is introduced as an intermediary device that performs the enumeration process with the host controller while consuming less than 100 mA. This intermediary then enables the main processor to be powered and enumerated successfully, acting as a bridge between the USB specification limits and the power requirements of the main processor
2Reliability
If the device uses a USB microcontroller to perform enumeration with less than 100 mA, then enumeration can succeed within USB specifications, but the device complexity increases
Solution Approach 1:
The device architecture is segmented into two distinct processing units: a USB microcontroller dedicated to handling USB enumeration and communication protocols, and a main processor for executing application functions. This segmentation allows the USB subsystem to be optimized for low-power enumeration while the main processor remains focused on its primary functions
3Power
If the device waits for battery charge before enumeration, then sufficient power is available, but loss of time occurs during the charging wait period
Solution Approach 1:
The USB microcontroller is designed to perform enumeration operations in advance, before the main processor needs to be fully powered. By completing the USB enumeration and device identification processes during the low-power phase, the system prepares the connection ahead of time so that when the main processor is activated, communication is already established
Data Source
AI summary
The proposed solution relates to enumeration of a handheld device by a host controller in a laptop, and more particularly to a method and apparatus to support USB enumeration of such a handheld device where greater than 100 mA is required to enumerate the chipset associated with the handheld device. The proposed solution comprises a handheld device with an added USB microcontroller. In operation, the integrated USB microcontroller is only powered up when the USB charging cable is plugged in and the rechargeable battery level is below the threshold required to power up the handheld device with less than 100 mA pre-enumeration USB current. The integrated USB microcontroller performs USB enumeration with the host controller using the pre-enumeration 100 mA current, so that the charging current can be increased to 500 mA post enumeration. Once the rechargeable battery is charged to above the threshold for the handheld device's chipset or when 500 mA current can be drawn from it, the chipset of the handheld device is powered up to take over USB communication from the USB microcontroller.