| General > General Technical Chat |
| They raised max USB output voltage from 5.25V to 5.50V. Retroactively. |
| << < (3/4) > >> |
| Siwastaja:
--- Quote ---The sensitivity will be mitigated in many cases by cable losses, so the devices themselves may never experience the 5.5V. --- End quote --- Are these guys serious, they don't understand Ohm's law and the fact that USB powers digital electronics which totally have a tendency of varying load from zero to maximum, so that voltage ratings would be exceeded at small load? |
| magic:
They had to justify it... somehow... ;D |
| thm_w:
--- Quote from: Siwastaja on November 01, 2023, 07:46:42 pm ---Are these guys serious, they don't understand Ohm's law and the fact that USB powers digital electronics which totally have a tendency of varying load from zero to maximum, so that voltage ratings would be exceeded at small load? --- End quote --- Yes thats what I said. It looks like this is a very old change, from 2014: https://web.archive.org/web/20211103140823/https://www.those.ch/designtechnik/wp-content/uploads/2014/08/USB-Type-C-Specification-Release-1.0.pdf The actual spec says it more reasonably: --- Quote ---4.4.2 VBUS The allowable default range for VBUS as measured at the DFP receptacle shall be as defined by the USB 2.0 Specification and USB 3.1 Specification. Note that due to higher currents allowed, legacy devices may experience a higher voltage (up to 5.5V maximum) at light loads. The DFP’s USB Type-C receptacle VBUS pin shall remain unpowered until a UFP is attached. The VBUS pin shall return to the unpowered state when the UFP is detached. See Table 4-15 for VBUS timing values. Legacy hosts/chargers that by default source VBUS when connected --- End quote --- Surprised that most people still quote the 5.25V number since that date. |
| magic:
--- Quote from: SiliconWizard on October 31, 2023, 09:01:43 pm ---They didn't bother to adjust the minimum Vbus as it didn't fit the rationale - AFAIR it was symmetric (4.75V to 5.25V), now it's going to be asymmetric. --- End quote --- Stop giving them ideas :-X Besides, that's the voltage at the root port, and various losses are permitted so that a compliant device actually needs to at least enumerate at supply as low as 4.4V. Chapter 7.2 of USB 2.0 specification. I'm pretty sure the original spec was simply copied from ATX, which is 5V ±5%. |
| SiliconWizard:
--- Quote from: magic on November 02, 2023, 06:03:21 pm ---I'm pretty sure the original spec was simply copied from ATX, which is 5V ±5%. --- End quote --- Yes, that's likely. |
| Navigation |
| Message Index |
| Next page |
| Previous page |