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USB Power Delivery Tester preview

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  • USB Power Delivery Tester preview


    The USB standard is complex. With the introduction of USB3.1 and Type-C connectors, it became really complex.
    Further, USB ports aren't just used for data transfer anymore, they are also used as a power supply source for a multitude of different peripheral devices. Some of which including phone chargers, fans, LED lights, hubs, docks, toys and many other unusual devices.

    In the USB 1.0 specs, a standard downstream port is capable of delivering up to 100mA at 5Volts, over 4 wires. (Two data wires, +5V and ground).

    In the USB 2.0 specs, a standard downstream port is capable of delivering up to 500mA at 5Volts, again over over 4 wires. (2.5 Watts) once a device is enumerated. The limit is just 100mA prior to enumeration.

    USB 3.0 ports add an additional row of five pins to make a total of nine wires. They are also able to supply more current. There are three kinds of USB port dictated by the 3.0 specs (and another specification known as the Battery Charging Specification, BC1.1 and then BC1.2)
    • A standard downstream port (SDP). Found on most computers, with a current limit of 500mA before enumeration and 900mA after enumeration.
    • A charging downstream port (CDP). Found on some computers, 1500mA (1.5A, 7.5W)
    • A dedicated charging port (DCP) for "dumb" wall chargers, also allowing 1500mA (1.5A, 7.5W)
    The USB 3.1 specification ports support 1.5A and 3A at 5V.

    USB Type-C Power Delivery

    With the Type-C connector the USB power delivery specification was also introduced, which allows power transfers of up to a massive 100W at varying voltages. The combination of a voltage level and current limit was referred to as a "profile".
    • Profile 1 (Default): 10 W (5 V @ 2 A)
    • Profile 2: 18 W (5 V @ 2 A -> 12 V @ 1.5A)
    • Profile 3: 36 W (5V @ 2 A -> 12 V @ 3A)
    • Profile 4 (Micro B/AB limit): 60 W (5 V @ 2 A -> 20 V @ 3 A)
    • Profile 5 (Standard B/AB limit): 100 W (5 V @ 2 A -> 20 V @ 5 A)
    Micro B/AB and Standard B/AB refer to the type of cable and connectors used. You can't use the small connectors at 100W (they have too much resistance and get too hot).

    Devices negotiate what power they need with the host via a new protocol. Ensuring that a device doesn't draw too much current, which would cause things to fail, catch on fire, melt or explode. The cables themselves also need to be intelligent cables containing a chip to indicate their capacity.

    More things to go wrong

    With this complexity there are a lot more things to go wrong. Typical faults include.
    • Vendors overstating the current limit of the host or USB charger
    • No overcurrent protection in some devices, increasing the changes of catastrophic failure.
    • Large voltage drops at high current levels over inferior cables, especially long cables
    • Voltage instability near the maximum current limit
    • Voltage instability resulting from sudden changes in current.
    • Various type of protocol errors in the power negotiation phase
    • Advertising incorrect profiles
    • Data corruption on the data lines during high current load on the power lines
    • Out of spec voltages
    • Too much ripple
    • Overheating when at maximum wattage
    When something does go wrong it is hard to know who to blame. The device or the host. It is also hard for vendors to test for compliance as there hasn't been any reasonably priced device on the market that could simulate a multitude of devices using the 5 electrical profiles listed above.

    Testing solution

    To fill the need for a testing solution we have spent the last 6 months working on a USB power delivery testing device. Features include,
    • Tests the power delivery capability of USB ports up to 100 Watts according to USB Battery Charging 1.2 and USB Power Delivery standards.
    • Detects proprietary chargers and adjusts the maximum current accordingly
    • Negotiates voltage levels with host PD controller chip to switch between different voltage levels from 5V to 20Volts.
    • Dissipates 50 watts of continuous load, and up to 100 watts for short periods (via dual fans & a large heatsink).
    • When used in conjunction with the USB loopback tester, tests communication speed, data integrity, and power delivery of USB ports simultaneously.
    • Current can be adjusted with milliamp precision using rotary dial or via PC software application.
    • Controllable and configurable over USB interface via an API to adjust the load.
    • Built-in protection against overcurrent, over voltage, over temperature and ESD.
    • Isolated USB Monitoring port which protects the monitoring machine.
    • Bootloader which allows updating the firmware in field.


    At the moment it is at the final prototype stage and we are about to go into mass production.

  • #2
    Here is a photo of the front of the USB power testing device.

    USB Power Tester prototype

    The three USB ports, are,

    Left: Monitoring port. This both powers the device and allows data logging back to a PC

    Middle: Connection of an optional downstream device (e.g. a USB3.0 loopback plug). Generally this port would only be used when you wanted to test data transmission at the same time as maximum power draw.

    Right: Connection to the USB power source to be tested. This can be a wall charger or a computer with a USB port (also known as the device under test).

    The rotary dial on the right is for adjusting the variable load & selecting the power profile to emulate.


    • #3
      Here is an image showing the LCD display under normal operation on a USB Type-C port with profile 5 (20V and 100W)

      USB Electrical Tester

      This shows the power tester running Profile 5 at 100Watts (20 V @ 5 A)

      The temperature of the heat sink is also shown. (There are thermal protection limits in place should it get too hot).

      The "LPK" indicator shows the current using used on the down steam port to the loopback plug. Not connected in this photo.


      • #4
        Here is an image showing the Type-C electrical profile selection.

        USB Type-C electrical profile selection

        The device can emulate any of these device profiles, by pushing the dial, then rotating the dial to select the desired profile to emulate.


        • #5
          Here is a screen shot for the prototype software that runs on a PC and logs the output of the USB power tester.

          USB power testing software screen shot

          The final version of the software should be a bit more tidy than the screen shot above. But it possible to monitor the voltage, temperature, power usage, maximum current draw allowed by the USB port. It also reports which profiles are available on the port & the user can set the load in mAmps.


          • #6
            By clicking on the IV Graph button (IV = Current vs Voltage) the device will sweep the full range of electrical loads to test the voltage stability over the entire output range.

            Typically as the current increases, resistance in the USB cable and in the motherboard hosting the USB port, results in a voltage drop. This graph provides an easy way to check the voltages remain in spec even under maximum load.

            USB3.1 Type-C Current Voltage graph


            • #7
              Here is a infrared photo from a thermal camera showing the heatsink in action.

              A heatsink is needed to dump the power coming out of USB port, which can be up to 100W for the new Type-C connector. The power tester can dump 50W on a continuous basis and up to 100W for short period (exactly how long depends on the ambient temperature & airflow)

              USB electrical load tester

              Also of interest is the temperature difference between the two cables. The cable carrying all the current is way hotter. Especially at the connector where the resistance must be slightly higher. This underlines the importance of having a good cable for high wattage applications.


              • #8
                USB power delivery test is finished and now available for sale ( product code PM110 ).

                Additional features added over the last couple of months include,
                - Measurement of voltage ripple (1Khz sampling rate)
                - Colour coded graphs
                - Improved logging
                - Power capacity measurement for power banks (in mAh)
                - Writing of the USB PD Tester's User's Guide.


                • #9
                  A photo showing the USB PD load tester being used by one of our customers doing hardware development with a 3rd party STI development board.
                  USB TypeC power delivery testing with development board