USB Type-C ECN - E-Marked Cable shall only use Vconn
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2020-11-27
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USB Type-C ENGINEERING CHANGE NOTICE
USB Implementers Forum
Form 20140811-ECN
Page: 1
Title: USB Type-C ECR E-marked Cables shall only use
VCONN
Applied to: USB Type-C Specification Release 2.0, August
2019
Brief description of the functional changes proposed:
All active cables except optically isolated active cables shall only be powered from Vconn unless VCONN is not present
in which case they can be powered by VBUS. Added a timing requirement to Table 4-6 for the switch from VBUS to
VCONN power.
Benefits as a result of the proposed changes:
VCONN was created specifically as the means to power the cable. When short active cables are powered from VBUS the
following issues occur:
1. USB PD Power Role Swap breaks the USB3 link.
2. Active cable compliance fixture becomes more complicated.
3. The VBUS power reported to the Sink is not correct as the cable is consuming power unless the cable modif ies the
Source capabilities which is complicated.
4. Cables are required to be tolerant to at least 21V.
An assessment of the impact to the existing revision and systems that currently conform to
the USB specification:
There are no known active cables released which pull power from VBUS.
An analysis of the hardware implications:
Some active cable designs that require Vbus will have to be redesigned to only consume VCONN.
An analysis of the software implications:
No impact to existing designs.
An analysis of the compliance testing implications:
Compliance is in development and can be modified to support this change.
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