Craft Calculator: some type C USB chargers do not recognize Raspberry Pi 4

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Some chargers do not seem to work with the new Raspberry Pi 4. This signals this Scorpia electronics blogTherefore, some users have been able to try this with a Macbook power supply, the Thunderbolt-3 plug while inserting it into the card, but this is not powered. Also, some other power supplies with USB Type-C connectors are affected.

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The author of the blog post, Tyler Ward, generally sees Thunderbolt 3 power supplies and adapters as inappropriate, capable of providing 5 amps of current. It also breaks the pattern with an electrical scheme: the USB-C connection requires two resistors instead of just one. For Raspberry Pi 4, the R79 resistor is connected to Configuration Channel (CC) 1 and to CC 2. "For most chargers this is not a problem as simple cables only use a DC cable"says Ward.

Recognized as an audio device

The problem with an active E-Mark chip cable inserted is that an additional pull-down resistor (Ra) is integrated into the cable. In combination with the pull-down resistor R79 (Rd), a total resistance of 836 ohms is obtained on both channels. These two values ​​interpret the charger according to the USB Type C standard (PDF) as if the Pi were an audio adapter that does not require power. Therefore, the craft computer is not powered. Active cables are often needed for power supplies with a power rating of over 60 watts and 5 amps. Typically, these are notebook power supplies.

An active cable has already integrated two Ra. (Image: (image: Scorpia)

Ward provides a detailed explanation of this behavior in his report and recommends the use of inactive cables for Raspberry Pi 4. These usually include the cables supplied with smartphones. Furthermore, it is likely that the old power supplies will work with a USB-A-USB-C adapter as long as they support sufficient power. Ward also hopes that future models of the Pi 4 will use a second DC resistor.

Ra is present when it measures 800-1.200 Ohm. (Photo: Scorpia)

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