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How Do DC Resistance Measurements Work with the Advanced Cable Tester v2?
Rena Ayeras

Question from the Customer:

I am using the Advanced Cable Tester v2 to evaluate USB-C to USB-C cables. Could you describe the theory of DC resistance measurement with the Advanced Cable Tester v2?  I also have questions about some of my test results.

Test Results 1:

This set of results shows failure on the GND Cable, GND Cable with shells, and Plug 2 Pin B1.

Active Type-C measurement with DC resistance measurement errors

My questions:

  • The failed resistance measurement of the GND Cable and the GND Cable with shells is 0.120 ohms. Why is the expected DC resistance set to 0.083 ohms? Is that parameter related to the voltage drop requirement of the USB Type-C specification?
  • Should I set up a different expected DC resistance for different E-mark ICs (3A or 5A)?
  • Can DC resistance test results be affected by the length of the Type-C to Type-C cable? Do I need to set up expected DC resistances that are related to the cable length?
Test Results 2:

  • As shown in figure below, the expected maximum resistance is set for 0.04 ohm for Plug 2: Pin B1. Does 04 ohm refer to low level contact resistance (LLCR) requirement in USB-C specification?
  • Does the DC resistance measurement result include the internal paddle card as well as the wire?
  • As indicated in the figure, the source is Plug 2: Pin B1, and sinks are plug 1: B4,A9,B9,A4 and plug 2: A4,A9,B4. Why is only one test result shown in the report? Does the report only show the maximum DC resistance value of the result?
Active Type-C measurement with DC resistance measurement errors Response from Technical Support:

Thanks for your questions! Current and voltage drops are factors of DC resistance, which we will describe in the next section. Then we will provide an overview of how DC resistance measurements are applied with the Advanced Cable Tester v2.

Effects of Current and Cable Length on DC Resistance

The expected or maximum DC resistance is derived from the USB Type-C specification. In the specification, "maximum voltage drop at maximum rated current", indicates that the resistance value will be different for 3A versus 5A cables. The maximum current is indicated in the E-Marker.

The length of the cable has no effect on resistance measurements. Typically, a shorter cable uses thinner wire stock, whereas a thicker cable uses thicker wire stock. Because of these physical elements, the maximum resistance remains constant regardless of the length of the cable.

Resistance Measurement Techniques

The 0.04-ohm measurement is similar to low-level contact resistance. To take this measurement, the Advanced Cable Tester v2 cycles through each pin and uses a 4-wire measurement technique as shown below.

4-Wire Measurement

Measuring Pin DC Resistance

  1. Current passes along the red path, which is a fixed 100mA.
  2. Sense1 is measured for one side of the pin; Sense2/Sense3/Sense4 are all measured as well, and resistance is calculated for each sense location.
  3. The lowest resistance is reported as the resistance of the pin.

There are cases where this may not provide exact information, but it does provide a good estimate of the low-level contact resistance of the pin. In most cases, the paddleboard of the connector is factored out.

Measuring Cable DC Resistance

To measure the whole-cable wire DC resistance, current is also injected into Rcpt1 pins 4, 9, 16, and 21, and applies sensors at Rcpt 2 pins 4, 9, 16, and 21. All four pins are used on each side and voltages are measured to calculate the resistance. The voltage can be measured in multiple places, which prevents misreadings due to a single bad pin.

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.