Citiram: |
USB devices must be capable of withstanding continuous exposure to the waveforms shown in Figure 7-1 while in any drive state. These waveforms are applied directly into each USB data pin from a voltage source with an output impedance of 39. The open-circuit voltage of the source shown in Figure 7-1 is based on the expected worst-case overshoot and undershoot. |
Citiram: |
A USB device must be able to withstand a continuous short circuit of D+ and D- to VBUS, GND, other data line, or the cable shield at the connector. |
Citiram: |
This ECN proposes to remove the 5V short circuit withstand requirement for the USB D+ and/or D- bus traces. |
Citiram: |
The 5V short circuit requirement limits the scalability of silicon fabrication processes moving forward. The advanced processes do not easily support this voltage level, which is 5X or more of the native process voltage. |
Citiram: |
The host and all self-powered hubs must implement over-current protection for safety reasons, ... Should the aggregate current drawn by a gang of downstream ports exceed a preset value, the over-current protection circuit removes or reduces power from all affected downstream ports. ... The preset value cannot exceed 5.0 A and must be sufficiently above the maximum allowable port current |
Citiram: |
If an over-current condition occurs on any port, subsequent operation of the USB is not guaranteed, and once the condition is removed, it may be necessary to reinitialize the bus as would be done upon power-up.
The over-current limiting mechanism must be resettable without user mechanical intervention. |