How are CC2 and VCONN Voltages Measured with the USB Power Delivery Analyzer?

Question from the Customer:

I’m starting to use the USB Power Delivery Analyzer. Looking at the power measurements, I see different voltages for the CC2 pin and VCONN. My understanding is VCONN reads 5V, but the VCONN is the voltage on the non-used CCx pin, which will read at 3V.  Can you explain why the voltage readings are different?

Response from Technical Support:

Thanks for your question! Following are a summary of how the USB Power Delivery Analyzer takes measurements, and the specifications per pin.

How the USB Power Delivery Analyzer Measures Power

The USB Power Delivery Analyzer is rated for 3A continuous and up to 20V on VBUS. It has two different ADCs (analog-to-digital converters) – because of this, you may see a variation based on the setup and orientation - the CCx and VCONN voltages are read by different ADCs. There are also maximum reading levels per pin, as described below.

Maximum Voltage and Reading Levels per Pin

  • CC1 - 3.3V
  • CC2 - 3.3V
  • CC2 - 5.25 V,  3A: (V-Vconn and I-Vconn, respectively)
  • VBus 5.25 V max, 3A (V-VBus and I-VBus, respectively)

Details about USB Power Delivery Analyzer Voltage Readings

Here are details about the voltage measurements:

  • CC1/CC2 Voltage - Up to 3.3V – this reading is useful for "traffic indication".
  • VCONN Voltage - Measured on CC2 signal (pin B5) of the USB Type-C  receptacle. Note - you may need to flip the USB PD analyzer over if VCONN ends up on the CC1 signal pin (A5).
  • VCONN Current - Measured across a 0.015 Ohm shunt resistor between the CC2 (pin B5) USB Type-C receptacle and the CC2 (pin B5) USB Type-C plug.
  • VBUS Voltage - Measured via an INA231 ADC (analog-to-digital converter) on the VBUS lines of the USB Type-C receptacle connector pins A4, A9, B4, and B9.
  • VBUS Current - Measured via an INA231 ADC across a 0.015 Ohm shunt resistor between the VBUS input Type-C receptacle and the VBUS Type-C plug.

Additional resources that you may find helpful include the following:

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