The Raspberry Pi 4's new USB-C charging doesn't work with some USB-C chargers

Another wonky USB-C implementation's to blame.

Credit: Raspberry Pi Foundation

The Raspberry Pi 4 launched in late June and as usual, it’s a major upgrade over the prior model, packing more RAM, enough graphics horsepower to drive a pair of 4K displays, and USB-C charging instead of micro-USB. But there’s a problem: The USB-C charging doesn’t work with some USB-C chargers.

Compatibility woes are nothing new with USB-C, but in this case, the problem lies with the Pi. As first described by Tyler Ward, the Raspberry Pi 4 uses “incorrect detection circuitry on the Pi end of the USB connection.” The $35 micro-PC shares a single resistor for two of the USB-C port’s pins, while the official USB-C spec calls for each pin to get a resistor of its own. This non-compliant design breaks functionality with more powerful “e-marked” cables, such as the USB-C chargers that ship with Apple’s MacBooks and some Windows 10 laptops.  

The Raspberry Pi 4 detects e-marked cables as an audio adapter accessory rather than a charger and refuses to use them to power up the board. USB-C issues aren’t an unheard-of problem, as the Nintendo Switch also packs a non-standard USB-C port that won’t work with all cables, and early phones and laptops equipped with USB-C charging could be fried by rogue cables.

raspberrypi4twoscreensh Raspberry Pi

Google engineer Ben Leung, a USB-C expert­-slash-vigilante known for calling out poor implementations, has weighed in the issue:

“Instead of trying to come up with some clever circuit, hardware designers should simply copy the figure from the USB-C Spec exactly. The Figure 4–9 I posted above isn’t simply a rough guideline of one way of making a USB-C receptacle. It’s actually normative, meaning mandatory, required by the spec in order to call your system a compliant USB-C power sink. Just copy it.”

Leung also says the Raspberry Pi team should’ve tested e-marked cables before shipping the board, as MacBook chargers aren’t exactly a rarity. “Raspberry Pi, you can do better,” he pleaded. “I urge you to correct your design as soon as you can so you can be USB-C compliant.”

raspberry pi charger Raspberry Pi Foundation

The official Raspberry Pi USB-C charger should work fine.

Fortunately, it sounds like that correction is already in the works. Pi co-creator Eben Upton told Tech Republic that he expects “this will be fixed in a future board revision,” and a Pi spokesperson confirmed to Ars Technica that a board revision with a compliant USB-C charging port should roll out in the “next few months.”

If you’ve already bought a Raspberry Pi 4, you can work around the charging issue by not using an e-marked cable. Options include using a USB-C phone charger, or picking up the official Raspberry Pi USB-C power supply for $8. It’s a shame that such a great piece of kit is suffering from such an easily avoided issue, but this isn’t the end of the world.

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Brad Chacos

Brad Chacos

PC World (US online)
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