What Details are Needed in the Profile to Accurately Run Type-C Cable Tests?

Question from the Customer:

I am starting to use the Advanced Cable Tester v2. I find the signal integrity eye diagrams easy to understand. The diagrams make sense to me as they correlate with the scope measurements in the lab.

I am curious about the accuracy of the GND/Shield resistance measurements. For example, one cable design has a frequent failure with the "GND Cable" test. Are there sensitivities of GND and Shield that I should look into?

Many failures that I have seen are marginal. Looking at the measurements I have taken, a lot of failed cables are over the expected value by just .040 ohms. How significant is this problem and what is the cause?

Another failure occurs with the E-Marker quiescent current. Is this due to the tolerance of Ra, or could something else be the cause?

Response from Technical Support:

Thanks for your questions! Some of test results that you see may be based on the version of the cable design. For example, the type and/or version of the electronic marker chip (E-Marker) can affect how the profile should be set up to run tests more accurately. There are other possible issues, such as the condition of the cable, the shell and plug materials, and more, which we will cover in the following sections.

Testing per Type-C E-Marker Requirements

It is good to review the cable profile with these questions:

  • Are the cables recent?
  • How current are the E-Marker specifications that were applied?

The requirements for Type-C cables have evolved, and there are requirements for specific performances (level of power delivery, speed of data transmission), which can greatly affect test requirements.

 

Adjusting Profiles per E-Marker

The values that are accepted can vary per version of requirement. For example – originally, the Quiescent Current "Initial" value was the only Type-C requirement, from r1.0 to about r1.2. Later, a new requirement was added to reduce the current consumption within 500ms.

In this case, many perfectly good cables will fail this requirement, especially when the cable is assembled with older designs. Such cables can still be "Certified", but that certification would be based on an earlier specification. It may be possible to get a waiver for a new cable design if that cable uses an earlier version of Certified E-Marker chip requirements.

Ra Resistance and Rp Pullup Current

In the current design, the E-Marker presents its Ra resistance and is detected by using the Rp pullup current. The port then turns on VCONN, typically between 3V and 5V. At this point, the E-Marker should power up, remove its Ra resistance (which is no longer needed) and reduce its current consumption below the steady-state threshold.

In earlier designs, Ra was often left enabled because the MCU was insufficiently optimized, or it took too much time to initialize. There are ways to modify the test for older designs:

  • In many cases, changing the Delay Time to 1s would allow this type of cable pass.
  • In other cases, it is desirable to simply disable this test.

Both changes can be implemented by creating a custom profile for the cable. Here is a summary of how to do that:

  1. Clone the "USB Full-Featured Type-C Cable, SuperSpeed Gen1, 3A" profile
  2. Set an appropriate Profile Name field
  3. Edit the E-Marker Quiescent Current section of the profile

 

GND Shield and Shell Resistances

There are factors that affect GND, SHIELD, and SHELL resistances, which are discussed in this section.

The plug shell and the receptacle shell do not mate with a gold-plated contact surface – which is how the other pins are built.  Instead, the shells can be plated with any metal - the stated requirement for the shell material is "shiny”. The shell is then covered in oils from manufacturing and subsequent handling. With this setup, the plug and the receptacle shells make contact with less than ideal results.

In addition, the shell specification does not require defining a maximum value of resistance. Total Phase has SHELL to SHELL profiles set to 1.5ohms, which is a high resistance value. This is an arbitrary default value that you can modify for your cable test.

Why GND Cable Failures Occur

The cables should have 100% gold-plated contacts. In most cases, factory fresh cables pass the first test, and only fail if allowed to oxidize during weeks of non-use, or from the normal wear that occurs after substantial insertion cycles.

When a GND Cable failure occurs for a new cable, most likely there is physically problem. In some cases, dirt is on the contacts of “factory fresh” cables. In this situation, the cables can be worn after light use, such as 10-20 insertion cycles.

GND Cable Measurements

The GND cable measurement is performed as follows:

  1. Source current on 4 pins and sink on the opposite 4 pins.
  2. Measuring the voltage at each of the tails of the receptacle pins.
  3. Calculate the resistance based on the measured actual current low and the voltages at each pin.

This measurement is very stable. As it is a small value, deviations can easily occur. Such measurements indicate a physical problem has occurred with the cable, such as oxidization or wear from use.

Single Pin Measurements

Measuring single pins is substantially more difficult than measuring GND cable. For measuring single pins, we recommend using a simplified version of a full cable measurement:

  1. Source only into 1 pin
  2. Sink from all 4 opposite pins
  3. Instead of measuring the source pin's voltage vs. the sink pin's voltage, measure the source pin vs. each of the other same-plug pins.

As no current is flowing through unused sense pins, this method allows measuring the voltage on the command area of the on the plug paddleboard. This way, you can determine the resistance of an individual pin.

Please note: This is not an official technique for measuring plugs; we developed this method at Total Phase to assist customers with their manufacturing. This technique has some caveats:

  • How PCB traces are routed on the paddleboard can skew this measurement.
  • Our 0.040 ohm threshold may be too strict for some scenarios in this situation, but it does allow new, good plugs to pass this test with acceptable margin.

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.

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