How Can Shield and Quiescent Current Failures Occur for USB-C and HDMI Cables that Seem to Work?

Question from the Customer:

I am using the Advanced Cable Tester v2 for testing cables. I have some questions about the test requirements and our results for USB-C and HDMI cables.

USB-C:
What is the Quiescent Current/E-Marker Steady State testing? We tested a lot of cables that all measured 0.00577A for the Steady State.

  • What is the requirement?
  • What are the details of the test?
  • Is it acceptable when measurements exceed the 0.004 specification?

HDMI:

  • Can you explain what TMDS_DATA0_SHIELD is testing? Our cables failed that test.
  • I assume it is checking that the pin-to-pin connection is there. However, I ran the same cables on a Pin-to-Pin tester and on a Quantum Data. In both of those cases, no issues were shown with the cables.

Response from Technical Support:

Thanks for your questions!  For information about quiescent current measurements, please refer to the document Universal Serial Bus Type-C Cable and Connector Specification, which is provided by USB.  Following are relevant excerpts from that document:

USB.org table that shows performance requirements for testing cables Power Characteristics for Active Cables

“The cable shall remove or weaken Ra when VCONN is in the valid voltage range (vVCONNValid). The cable shall reapply Ra when VCONN falls below vRaReconnect as defined in Table 4-6. The cable shall discharge V CONN to below vVCONNDischarge on a cable disconnect. The cable shall take into account the V CONN capacitance present in the cable when discharging VCONN.”

Source:  USB.org

Cable Test Requirements

The Advanced Cable Tester v2 measures the current that the cable consumes initially and when the cable is idle. This requirement was made stricter a few years ago. Initially, that requirement was more lenient. The addition is reducing power below 75mW. That requirement was added after several cables were released and the E-Marker silicon was already certified.

Many otherwise good cables do not comply with that requirement, and here are the reasons why the cables are functional:

  • The impact to end-users is that the battery life may be minimally affected. Otherwise, no noticeable effects occur.
  • Typically, hosts do not have to provide VCONN to cables that are identified as passive.

However, there appears to be an issue with the cables that you are testing.

  • The TMDS_DATA0_SHIELD continuity test measures that the shield pin is connected through.
  • Pin8 should connect to the shield that wraps around the DATA0 pins that are attached to pins 7 and 9.

Signal Integrity vs Pin-Shield Tests

Regarding your cable, the shield-pin connection does not appear to be good. Does your pin-to-pin tester test the shield?

It is possible a Quantum Data tester would pass a cable with that flaw. That shielding is not essential for communication. However, it is a required part of the specification. You can see that even with the Advanced Cable Tester v2, your cables passed the signal integrity test for DATA0. However, the lack of correct shielding might hurt the EMI performance of the cable.

We hope this answers your questions. Additional resources that you may find helpful include the following:

If you want more information, feel free to contact us with your questions, or request a demo that applies to your application.