4 ms·

You can’t make that assumption at the end. These cables are as thin as they can possibly be to carry the maximum current they’re rated for. That maximum current

You can’t make that assumption at the end. These cables are as thin as they can possibly be to carry the maximum current they’re rated for. That maximum current could be 0.5A or it could be 5A. Try to pull 5A through a cable rated for 0.5A and you’re likely to burn the customer’s house down. You can’t really measure the resistance of the cable from one end. You can try to guess by watching for a voltage drop as you pull more current, but that’s extremely error prone. Because of this, all of the components are supposed to signal what they can handle, and if they don’t, they fall back to the minimum current known to work.

thfuran 8y ago
Wait, so a USB-C cable cannot be a completely passive component?
- barbegal 8y ago
  The resistor in the USB-C cable to identify its current carrying capacity is still a passive component. And of course you can omit this resistor but your device will fall back to the minimum current.
- andromeduck 8y ago
  They can be passive - thus the resistor to incidicate the cable's rating.
- deleted 8y ago
  [deleted]
- digi_owl 8y ago
  Yes and no. There is no IC in there, but there are small segment in the cable spec that talks about resistors on one of the lines that signal the type of cable available. So you put one resistor in for a low rated C to C cable, another for a higher C to C rated, and yet another for an A to C converter (indicating that the C end should fall back to the older battery charging spec). Guess how many fly by night cable manufacturers get those wrong... the C to C spec charging, or Power Delivery, spec is a whole different barrel of stinking fish. Where you can have everything from 0.5A at 5V to multiple As at 20V running over the same C to C cable. This is akin to the Qualcomm quickcharge scheme that run 9V over existing micro-USB cables and ports (thus allowing higher wattage without cranking up the amps).
  - kevin_thibedeau 8y ago
    Power Delivery is not just for USB-C. It was defined for use with USB 2.0 and up on any of the legacy connectors.
    - digi_owl 8y ago
      While true on paper, i wonder if it will ever be implemented as such. And frankly it may well be yet another black mark on the mess that is USB "C" (or 3.1 or whatever).

thfuran 8y ago

Wait, so a USB-C cable cannot be a completely passive component?

barbegal 8y ago
The resistor in the USB-C cable to identify its current carrying capacity is still a passive component. And of course you can omit this resistor but your device will fall back to the minimum current.
andromeduck 8y ago
They can be passive - thus the resistor to incidicate the cable's rating.
deleted 8y ago
[deleted]
digi_owl 8y ago
Yes and no. There is no IC in there, but there are small segment in the cable spec that talks about resistors on one of the lines that signal the type of cable available. So you put one resistor in for a low rated C to C cable, another for a higher C to C rated, and yet another for an A to C converter (indicating that the C end should fall back to the older battery charging spec). Guess how many fly by night cable manufacturers get those wrong... the C to C spec charging, or Power Delivery, spec is a whole different barrel of stinking fish. Where you can have everything from 0.5A at 5V to multiple As at 20V running over the same C to C cable. This is akin to the Qualcomm quickcharge scheme that run 9V over existing micro-USB cables and ports (thus allowing higher wattage without cranking up the amps).
- kevin_thibedeau 8y ago
  Power Delivery is not just for USB-C. It was defined for use with USB 2.0 and up on any of the legacy connectors.
  - digi_owl 8y ago
    While true on paper, i wonder if it will ever be implemented as such. And frankly it may well be yet another black mark on the mess that is USB "C" (or 3.1 or whatever).