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Raspberry Pi admits to faulty USB-C design on the Pi 4
The Raspberry Pi 4 was announced two weeks ago as a major new upgrade to the line of cheap single-board hobbyist computers. The Pi 4 featured a faster CPU, options for up to 4GB of RAM, and a new, modern USB-C port for power delivery. The Pi 4 was the Raspberry Pi Foundation's first ever USB-C device, and, well, they screwed it up.
As detailed by Tyler Ward, the Raspberry Pi 4 has a non-compliant USB-C charging port and doesn't work with as many chargers as it should. Thanks to the open nature of Raspberry Pi (even the schematics are online!), Ward was able to discover that Raspberry Pi just didn't design its USB-C port correctly. Two "CC" pins on a USB-C port are supposed to each get their own 5.1K ohms resistor, but Raspberry Pi came up with its own circuit design that allows them to share a single resistor. This is not a compliant design and breaks compatibility with some of the more powerful USB-C chargers out there.
[...] The Pi 4 is not the first high-profile device to get the USB-C spec wrong. The Nintendo Switch also has a non-compliant USB-C port and has issues with certain USB-C cables as a result.
After reports started popping up on the Internet, Raspberry Pi cofounder Eben Upton admitted to TechRepublic that "A smart charger with an e-marked cable will incorrectly identify the Raspberry Pi 4 as an audio adapter accessory and refuse to provide power." Upton went on to say, "I expect this will be fixed in a future board revision, but for now users will need to apply one of the suggested workarounds. It's surprising this didn't show up in our (quite extensive) field testing program."
Probably not a dealbreaker (the cables that do work are cheaper), but could be annoying.
Previously: Raspberry Pi 4 Model B Launched
(Score: 2) by RS3 on Thursday July 11 2019, @04:09AM
Awesome post- I'm in strong agreement mostly.
Mounting on a PC board- surface or through-hole- _any_ mechanical connector, switch, button, pot, etc., that humans touch or gets mechanical stress is piss-poor design IMHO. That's why I suggested the dongle for the power connector. I know, I hear it now, it's supposed to be cheap. But you can find connectors with through-hole reinforcements (and even they break easily...)
My only issue with your post: I would NOT use a diode bridge. Of course I know why you suggested it, but think about the ground (electrical return or common) problem. If you use a bridge, then the car's (or anything's) ground is NOT Pi ground- there's a diode separating the two. I'd just use a single diode to guard against reverse-polarity and that's good enough.
I'm not against switching supplies, but you make good points about the RFI. They can be shielded, and properly designed so as to minimize / damp out RFI-producing ringing. In fact, for something this small there are some great regulator chips that run with one inductor and minimal RFI.
As much as I am an analog/linear EE and generally prefer simpler linear regulators, at 3 A drawn, running off a car's electrics would cause a 7805 to dissipate almost 30 watts, and that's not a small heatsink. Oh, and oops- a 7805 is only good for 1.5 A, so a current-passing booster transistor is needed (easy). Still 30 W to unload.
More research needed...