Reverse polarity protection is often not done with diodes for the reasons explained. It is more common to use a p-channel MOSFET (or ideal diode controllers when there are multiple power sources) when more than a trivial amount of power is used by the design. They are not cheap when properly sized, but are not ruinously expensive either and are not too large for most designs.
Bad USB-C cable destroys laptop
11–20 of 146 posts
Re: Bad USB-C cable destroys laptop
#12HN has previously had a story on the author, a Google engineer who tests USB-C cables on Amazon to make sure they're spec-compliant. He does some amazing work:
https://news.ycombinator.com/item?id=10508494
I don't have any devices right now that use USB-C, but whenever I see a deal pop up for one, I usually check the Amazon listing to see if this guy has reviewed/certified the cable yet.
I recommend others do the same. It's not worth damaging your $800+ laptop because you wanted to save $10 on a cable.
Re: Bad USB-C cable destroys laptop
#13My biggest surprise here is there is still people using Google+.
I think he works for Google.
Yep, not sure what he does these days but on some of his old reviews he noted that he's a software engineer on the ChromeOS/Pixel team: http://www.amazon.com/gp/review/R2DQ7OH7PQG24F
Re: Bad USB-C cable destroys laptop
#14I wonder if this one cable was miswired or it's something consistently wrong with the product. Either way that something like that could make it out of the factory demonstrates terrible or no QA/QC. I've never used the Twinkie but it looks pretty cool. This shows that it may be worth adding some simple protection to the circuit to prevent simple miswires from damaging it or the host PC.
Yeah, that's what the amazon review details. The ground is miswired.
The question isn't what was wrong with the cable, but whether it was just this one specific cable, or whether it's all of the cables in from this production run.
Re: Bad USB-C cable destroys laptop
#15HN has previously had a story on the author, a Google engineer who tests USB-C cables on Amazon to make sure they're spec-compliant. He does some amazing work: https://news.ycombinator.com/item?id=10508494 I don't have any devices right now that use USB-C, but whenever I see a deal pop up for one, I usually check the Amazon listing to see if this guy has reviewed/certified the cable yet. I recommend others do the sam…
Another user has compiled Benson's reviews into a Google spreadsheet:
https://docs.google.com/spreadsheets/d/1wJwqv3rTNmORXz-XJsQa...
Re: Bad USB-C cable destroys laptop
#16Reverse polarity protection is often not done with diodes for the reasons explained. It is more common to use a p-channel MOSFET (or ideal diode controllers when there are multiple power sources) when more than a trivial amount of power is used by the design. They are not cheap when properly sized, but are not ruinously expensive either and are not too large for most designs.
[deleted]
Re: Bad USB-C cable destroys laptop
#17TL;DR; USB-C cable had GND tied to Vbus and Vbus tied to GND (opposite as it should be) Honestly, I'm surprised that this isn't something that thelaptop and other such USB adapters aren't equipped to deal with. This is only slightly worse in my book than a USB adapter being fried from shorting the Vbus and GND pins together
Why would you design in reverse polarity protection? It adds cost, and the mechanical connector already makes it impossible for VDD to short to GND in USB type C because of its rotational symmetry.
Re: Bad USB-C cable destroys laptop
#18TL;DR; USB-C cable had GND tied to Vbus and Vbus tied to GND (opposite as it should be) Honestly, I'm surprised that this isn't something that thelaptop and other such USB adapters aren't equipped to deal with. This is only slightly worse in my book than a USB adapter being fried from shorting the Vbus and GND pins together
Why would you design in reverse polarity protection? It adds cost, and the mechanical connector already makes it impossible for VDD to short to GND in USB type C because of its rotational symmetry.
unless the connector were cut, or some other catastrophic failure. I tend to think ruining a devices USB controller should be near impossible short of something like the USB killer (http://arstechnica.com/security/2015/10/usb-killer-flash-dri...)
Re: Bad USB-C cable destroys laptop
#19Reverse polarity protection is often not done with diodes for the reasons explained. It is more common to use a p-channel MOSFET (or ideal diode controllers when there are multiple power sources) when more than a trivial amount of power is used by the design. They are not cheap when properly sized, but are not ruinously expensive either and are not too large for most designs.
There should be a crowbar diode between the rails. If the design is too cheap for an input fuse, the source will limit/disable the short current.
Re: Bad USB-C cable destroys laptop
#20TL;DR; USB-C cable had GND tied to Vbus and Vbus tied to GND (opposite as it should be) Honestly, I'm surprised that this isn't something that thelaptop and other such USB adapters aren't equipped to deal with. This is only slightly worse in my book than a USB adapter being fried from shorting the Vbus and GND pins together
Why would you design in reverse polarity protection? It adds cost, and the mechanical connector already makes it impossible for VDD to short to GND in USB type C because of its rotational symmetry.
I constantly have Vdd shorts due to ground loops when measuring stuff. But a more frequent case is worn out cables (every lightning cable I've owned has eventually broke).
Its not rare enough of a failure mode to ignore.