How Can I View the Resistor Values of a USB Type-C Cable with the USB Power Delivery Analyzer?

Question from the Customer:

We’re testing our new design, a Type-C captured cable AC home charger, with your USB Power Delivery Analyzer.

 USB Power Delivery Analyzer
USB Power Delivery Analyzer

The charger is not a Power Delivery (PD) device, but it is Type-C compliant. Looking at the data, we saw that the 5V VBUS was active at T=0 and the phone started charging. However, there was little indication of communication.  The only real comment we saw was “PD Fraction” - what does that mean?

What we are really looking to read is the “e-marker” resistor.  We do have the voltage value coming from the CC line – how do we get the e-marker resistor value?

Response from Technical Support: Thanks for your question! The "PD Fraction" or "PD" message indicates that our decoder found transitions on the CC lines and could not fit that information into a packet, which can be described as "leftover bits." In this case, the CC column in the Data Center Software transaction window indicates the data was on CC2. The 5V that you see applied is being used as VCONN: as specified, CC2 is used for VCONN. Most likely, those extraneous “leftover bits” are contact bounce or other electrical noise.

To determine the actual resistor values, you can calculate that value from the (approximately 1.65 volts measured in the graph on CC1).  With a 5.1K pull-down and a 10K pull-up to 5V, the calculation results in 1.69V, which effectively matches the 1.65V readings on the trace. In this case, the 10K pull-up indicates a 3A supply.

Note: This method of supply characterization depends on the value of the pull-down resistor of the device that is being charged. In this case, the calculations look correct. For more information about voltage and current measurements, please refer to our knowledge base article KB160401 - Voltage and Current Measurements with the USB PD Analyzer.

Additional resources that you may find helpful include:

We hope this answers your questions. If you have other questions about our analyzers or other Total Phase products, feel free to email us at sales@totalphase.com, or if you already own one of our devices and have a technical question, please submit a request for technical support.

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