100 lines
6.3 KiB
Markdown
100 lines
6.3 KiB
Markdown
The USB-C cable tester shows which features a USB-C to USB-C cable supports.
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<img src="picture/v3_front.webp" title="front" height="250"/>
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<img src="picture/v3_back.webp" title="back" height="250"/>
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purpose
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=======
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USB-C to USB-C cables come in a several flavours.
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The [USB Type-C Cable and Connector Specification](https://www.usb.org/document-library/usb-type-cr-cable-and-connector-specification-revision-21) lists two types of cables:
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- Standard: this supports USB 2.0 data transfer, as well as Power Delivery (PD)
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- Full-Featured: this adds differential pairs used for SuperSpeed (SS) data transfer (for USB3, USB4, ...), and sideband use (SBU) for alternate modes or USB4 data transfer
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On top of that, cables can be electronically marked (eMarked).
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Full-Featured cables should be electronically marked, while this is optional for standard cables.
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eMarked cables include chips that communicate on the CC wire using the PD protocol.
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They provide information about the cable, and are mandatory (but not sufficient) for 5A current transfer (e.g. for 100W charging) instead of the standard 3A (e.g. 60W).
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Then there are not specification compliant cables, that only support charging, or no PD communication.
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I suspect some full-featured cables are not electronically marked, and most magnetic cables are not shielded, at least not from plug to plug.
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Because what is inside of the cable is not indicated on the outside, the cable tester checks for the individual capabilities.
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usage
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=====
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Ensure a non-empty CR1220 battery is in the tester.
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Plug both ends of the USB-C cable in the tester and read the lights:
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<img src="picture/v3_ff.webp" title="Full-Featured cable" height="250"/>
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- SHIELD: ensures the cable is shielded, important for super speed data transfer.
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- POWER: ensures the VBUS and GND wires are present, required to power a device.
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- USB2: ensures the D+ and D- wires are present, required for USB data transfer (up to at least 2.0).
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- CC/PD: ensures the Configuration Channel (CC) wire is present, required to determine the plug orientation and for Power Delivery (PD) communication (used for fast charging)
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- SS: ensure the 4 differential pairs are present, required for Super Speed (SS) data transfer (USB3, USB4, ...)
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- SBU: ensures the Side Band Use (SBU) wires are present, used for alternate modes.
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- eMarker: indicates if the cable is electronically marked, required to support 5A/100W power transfer.
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Note: the eMarker indication does not mean the cable does support 5A/100W power transfer.
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Most of the time, an electronically marked cable does support 5A, since the chip costs more than the wire.
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But to confirm it, this information needs to be read out from the chip inside the cable using the PD protocol.
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The cable tester does not support this functionality.
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Some USB Power Monitor (UPM) provide this functionality.
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mode of operation
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=================
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Here the methods used to test the different capabilities of the cable:
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- POWER: ensures the VBUS and GND wires are present in the cable, required to power a device.
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Although there 4 ground and 4 power pins, there are only 1 ground and 1 power wires.
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The pins are inter-connected in the plugs on each side of the cable.
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- SHIELD: ensures the shell of the plugs are connected on both sides of the cable.
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It also ensures the shield is grounded, as required by the specification.
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This does not verify if the cable has proper shield foil and braid though, or it's just a wire (I haven't seen a cable cheating this way yet).
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Also, if the cable has a shield, but only connected on one plug or it is not connected to ground, this will not be detected.
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- USB2: ensures the UTP wire are present, used for USB 2.0 data transfer.
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There is only one pair of UTP wire for the Dp and Dn signals using for USB 2.0 communication, connected to A6 and A7 on both sides.
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Since the plug is reversible on both sides, we short the pins to be sure we can test the cable.
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- SS: ensures the SuperSpeed (SS) wires are present, for USB3 (and USB4) data transfer.
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There are 4 pairs of wires (SDPxx) used for differentials signals.
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The tester checks if all are present.
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- SBU: ensures the sideband use (SBU) are present, used for Alternate Modes.
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There are 2 single SBU wires.
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The tester checks if all are present.
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- CC: ensures the Configuration Channel is present, used for Power Delivery (PD) communication.
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There is one wire going from CC1 on one side of the connector, to CC1 on the other side of the connector.
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Since the plug on both sides is reversible, there are 4 possible permutations.
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This pin is actually used to determine the orientation of the plug, and do the date signal switching on the right pins.
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Which of both LEDs is on also depends on the plug orientation.
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- eMarker: indicates if the cable is electronically marked.
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The detection is the complicated part of this design.
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A5 on both sides are interconnected through the CC wire.
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B5 on both sides are connected to Vconn.
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Vconn only allows to power the embedded chip, but does not provide B5 interconnection.
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The connected device can detect the presence of the chip, by checking if B5 (on each side) is pulled down using Ra (~ 1kOhm).
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It can then provide power on Vconn.
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The cable tester detects electronically marked cables the following way.
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If Ra is present, the gate voltage of a p-channel MOSFET on the tester is pulled low, powering the corresponding LED.
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By default the gate is pulled up by the resistor used for the CC LED.
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When Ra is present, it is on both plugs of the cable.
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Thus it is enough to detect is on one plug.
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Because it can be on A5 or B5 pins, the detection circuit needs to be on both pins.
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On the other plug, the CC pins can't be interconnected, else the voltages is pulled to low for the CC LED to work.
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Thus, two separate LEDs are used to detect CC.
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The pull-up resistor needs to be as high as possible to, for the Ra pull-down resistor (800-1200 Ohm) to work properly, activating the gate.
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The BSS84 pMOS has a Vgs of ~1.7V.
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A pull-up resistor of 2.2 kOhm is sufficient (with a 3V battery).
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Green LEDs are used for CC.
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Although they have a higher voltage drop, they seems to be more efficient.
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With a 2.2 kOhm, it produces a bright enough light.
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Warning: because green LED has a forward voltage drop of ~2V to ground, the battery voltage can't be higher than 3.3V, else the gate voltage will exceed the threshold and the eMarker LED will be on, which is a false positive.
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