Hi all.
There has been a lot of confusion on the Type-C / USB 3.1 spec, how it relates to charging USB Type-C devices, and what kind of data speeds you can get from Type-C devices. I did a fair bit of fact finding, and thought I'd consolidate everything I learned into one topic. I'm not going to post everything you could ever know about USB specs here, but the technical docs are quite... well... technical. I'm going to try to keep it focused on items as they relate to the new Nexus phones. As always, if you find this helpful, I'd appreciate the :good:.
Resources:
http://www.usb.org/developers/docs/ (Specifically: http://www.usb.org/developers/docs/usb_31_072715.zip)
http://arstechnica.com/gadgets/2015/...ese-usb-specs/
http://www.cnet.com/news/usb-type-c-...nect-them-all/
Attachment 3501211
To start, it should be noted that USB Type-C is not specified in any way in the USB 3.1 specifications. USB Type-C is a separate USB specification, not an adjustment to existing specifications. USB Type-C has been designed separately to include compatibility for USB 2.0 and USB 3.1. In short: USB 3.1 does not support Type-C; rather, Type-C supports USB 3.1 (and USB 2.0). This backwards compatibility is an important distinction to make, as Type-C capabilities exceed USB 3.1 / 2.0 specifications.
I've also created an excerpts pdf highlighting some of the items from the USB.org documents which I found informative. You'll need WinRAR or other utility to extract the .pdf from the .rar file.
One of the biggest questions floating around right now on the forum is what charger will work with my new Nexus, and will it support fast charging? To determine that, we look at known chargers (the OEM ones from Google) which support fast charging. Those chargers have the following characteristics: USB Type-C connector. Output of 5 Volts at 3 Amps (15 Watts). Looking at the spec docs, this directly coincides with the Type-C 3A charging spec. This is the highest power state a Type-C connection can provide without being rated and compliant with USB PD (Power Delivery) specs. See Table 2-1 (page 23) in the excerpts doc.
What if my USB charger only outputs 2.0A? According to the documentation I've read, the devices must negotiate which charging state can be used when they are connected. In this case, the phone can accept 5V @ 3A, but the charger can't supply it. It falls back to the next highest state that both devices can accept. (See page 149, table 4-12 for order of precedence.) If the charger is compliant with Type-C 1.5A or USB BC 1.2 specs, it falls back to 5V @ 1.5A (7.5W). If not, it falls back to USB 3.1 defaults of 5V @ 0.9A (4.5W), or worst case scenario of USB 2.0 defaults of 5V @ 0.5A (2.5W). As you can see, there is a big difference between 15 watts for fast charging and 2.5 watts for USB 2.
What happens if I use a USB Type A connection or adaptor with my Nexus? These are your typical square USB 2.0 / 3.0 connections we are all used to seeing. The CNet article linked above does a reasonable job of explaining the ports and the max power output of each connection type, although they don't mention anything about USB BC 1.2 (battery charge) specs, nor do they dive deeper into the individual Type-C specs. It does list the USB 3.1 power profiles available, specifically a profile for 5V @ 2A (10W). The 2A current level is absent from the USB Type-C documentation I've read, so it is unclear whether it is a useable state for charging our devices. In any regard, consider USB Type A and B connectors to be the weak link in device charging. Plug your Nexus into a USB 2.0 port and you'll charge very slowly. Plug it into a 3.0 port, and you'll charge less slowly. Plug your USB Type-C cable into a USB Type-C port, and you'll be able to fast charge.
What connection speeds will I get on my Nexus using Type-C? I didn't include it in the excerpts doc, but if you look at the "USB Type-C Specification Release 1.1.pdf" doc from USB.org, it defines on page 19 the types of plugs and cables for Type-C, including a USB 2.0 Type-C plug. Starting at page 57 it defines all of the wires/pins for the different cables. Comparing table 3-10 to 3-11, you can see that all of the SDP (shielded differential pair) signal pins/wires are missing in the USB 2.0 Type-C connections. These are your high speed data connection wires. The Vbus, Vconn, cc, GND wires are all still present to support Type-C power delivery. So, in other words, OEMs can choose to implement a cheaper and slower Type-C connection type for devices which don't require up to 100 watts of power, or won't use up to 10GB/s transfer speeds. The Nexus 5X & 6P fall into this category. Kind of disappointing; however, understandable considering the specs as USB-IF has defined them - OEMs only have 2 choices: USB Full-Featured Type-C standard or the USB 2.0 Type-C standard. I'm sure one is more expensive than the other. Anyway, I'll digress, as all of this only points in the direction of the answer to our original question. What connection speeds are you going to get with the Nexus? USB 2.0 speeds.
What about QuickCharge 2.0/3.0 chargers!? My Nexus has a Qualcomm chip, isn't it compatible? No. It's not implemented in the new Nexus devices. It is also unclear at this time as to which 5V current the Nexus will draw from such a charger using a Type-A adaptor. QuickCharge works by increasing voltage and amperage to charge quickly. The USB Type-C standard only works this way in USB PD modes, otherwise voltage never varies from 5V. Considering that QuickCharge 2.0/3.0 is completely different from USB PD, and if I had to venture a guess, I would say that the best charging you would get out of Nexus device plugged into a QuickCharge charger would be 5V at 1.5A (10W), assuming QuickCharge was able to recognize/negotiate with a compatible USB BC 2.1 device. Worst case would be it sends 12V at 3A (36W) to your phone and your Nexus dies in a exploding lithium maelstrom of fiery chaos. That's pure speculation on my part though.
So, how should you approach charging and connecting your Nexus to other devices? The same way you would any other device - plug it into the best thing you have available. For plugging into computers, use the best port you have available. Type-C to Type-C > USB 3.x to Type-C > USB 2 to Type-C. For 3rd party chargers, try to match OEM specs: 5 volts at 3 amps output using a Type C connector. If you have to use an adaptor (Type-A to Type-C), you're just going to get what you get - it all depends on how the 2 devices negotiate power profiles for charging.
If I left any glaring omissions from this, please follow up. I'd love to have all the info we can get. If you just want to point out some minute nuance of how I'm wrong, and get into a pissing match over who's right, do the community a favor and just PM me.
There has been a lot of confusion on the Type-C / USB 3.1 spec, how it relates to charging USB Type-C devices, and what kind of data speeds you can get from Type-C devices. I did a fair bit of fact finding, and thought I'd consolidate everything I learned into one topic. I'm not going to post everything you could ever know about USB specs here, but the technical docs are quite... well... technical. I'm going to try to keep it focused on items as they relate to the new Nexus phones. As always, if you find this helpful, I'd appreciate the :good:.
Resources:
http://www.usb.org/developers/docs/ (Specifically: http://www.usb.org/developers/docs/usb_31_072715.zip)
http://arstechnica.com/gadgets/2015/...ese-usb-specs/
http://www.cnet.com/news/usb-type-c-...nect-them-all/
Attachment 3501211
To start, it should be noted that USB Type-C is not specified in any way in the USB 3.1 specifications. USB Type-C is a separate USB specification, not an adjustment to existing specifications. USB Type-C has been designed separately to include compatibility for USB 2.0 and USB 3.1. In short: USB 3.1 does not support Type-C; rather, Type-C supports USB 3.1 (and USB 2.0). This backwards compatibility is an important distinction to make, as Type-C capabilities exceed USB 3.1 / 2.0 specifications.
I've also created an excerpts pdf highlighting some of the items from the USB.org documents which I found informative. You'll need WinRAR or other utility to extract the .pdf from the .rar file.
One of the biggest questions floating around right now on the forum is what charger will work with my new Nexus, and will it support fast charging? To determine that, we look at known chargers (the OEM ones from Google) which support fast charging. Those chargers have the following characteristics: USB Type-C connector. Output of 5 Volts at 3 Amps (15 Watts). Looking at the spec docs, this directly coincides with the Type-C 3A charging spec. This is the highest power state a Type-C connection can provide without being rated and compliant with USB PD (Power Delivery) specs. See Table 2-1 (page 23) in the excerpts doc.
What if my USB charger only outputs 2.0A? According to the documentation I've read, the devices must negotiate which charging state can be used when they are connected. In this case, the phone can accept 5V @ 3A, but the charger can't supply it. It falls back to the next highest state that both devices can accept. (See page 149, table 4-12 for order of precedence.) If the charger is compliant with Type-C 1.5A or USB BC 1.2 specs, it falls back to 5V @ 1.5A (7.5W). If not, it falls back to USB 3.1 defaults of 5V @ 0.9A (4.5W), or worst case scenario of USB 2.0 defaults of 5V @ 0.5A (2.5W). As you can see, there is a big difference between 15 watts for fast charging and 2.5 watts for USB 2.
What happens if I use a USB Type A connection or adaptor with my Nexus? These are your typical square USB 2.0 / 3.0 connections we are all used to seeing. The CNet article linked above does a reasonable job of explaining the ports and the max power output of each connection type, although they don't mention anything about USB BC 1.2 (battery charge) specs, nor do they dive deeper into the individual Type-C specs. It does list the USB 3.1 power profiles available, specifically a profile for 5V @ 2A (10W). The 2A current level is absent from the USB Type-C documentation I've read, so it is unclear whether it is a useable state for charging our devices. In any regard, consider USB Type A and B connectors to be the weak link in device charging. Plug your Nexus into a USB 2.0 port and you'll charge very slowly. Plug it into a 3.0 port, and you'll charge less slowly. Plug your USB Type-C cable into a USB Type-C port, and you'll be able to fast charge.
What connection speeds will I get on my Nexus using Type-C? I didn't include it in the excerpts doc, but if you look at the "USB Type-C Specification Release 1.1.pdf" doc from USB.org, it defines on page 19 the types of plugs and cables for Type-C, including a USB 2.0 Type-C plug. Starting at page 57 it defines all of the wires/pins for the different cables. Comparing table 3-10 to 3-11, you can see that all of the SDP (shielded differential pair) signal pins/wires are missing in the USB 2.0 Type-C connections. These are your high speed data connection wires. The Vbus, Vconn, cc, GND wires are all still present to support Type-C power delivery. So, in other words, OEMs can choose to implement a cheaper and slower Type-C connection type for devices which don't require up to 100 watts of power, or won't use up to 10GB/s transfer speeds. The Nexus 5X & 6P fall into this category. Kind of disappointing; however, understandable considering the specs as USB-IF has defined them - OEMs only have 2 choices: USB Full-Featured Type-C standard or the USB 2.0 Type-C standard. I'm sure one is more expensive than the other. Anyway, I'll digress, as all of this only points in the direction of the answer to our original question. What connection speeds are you going to get with the Nexus? USB 2.0 speeds.
What about QuickCharge 2.0/3.0 chargers!? My Nexus has a Qualcomm chip, isn't it compatible? No. It's not implemented in the new Nexus devices. It is also unclear at this time as to which 5V current the Nexus will draw from such a charger using a Type-A adaptor. QuickCharge works by increasing voltage and amperage to charge quickly. The USB Type-C standard only works this way in USB PD modes, otherwise voltage never varies from 5V. Considering that QuickCharge 2.0/3.0 is completely different from USB PD, and if I had to venture a guess, I would say that the best charging you would get out of Nexus device plugged into a QuickCharge charger would be 5V at 1.5A (10W), assuming QuickCharge was able to recognize/negotiate with a compatible USB BC 2.1 device. Worst case would be it sends 12V at 3A (36W) to your phone and your Nexus dies in a exploding lithium maelstrom of fiery chaos. That's pure speculation on my part though.
So, how should you approach charging and connecting your Nexus to other devices? The same way you would any other device - plug it into the best thing you have available. For plugging into computers, use the best port you have available. Type-C to Type-C > USB 3.x to Type-C > USB 2 to Type-C. For 3rd party chargers, try to match OEM specs: 5 volts at 3 amps output using a Type C connector. If you have to use an adaptor (Type-A to Type-C), you're just going to get what you get - it all depends on how the 2 devices negotiate power profiles for charging.
If I left any glaring omissions from this, please follow up. I'd love to have all the info we can get. If you just want to point out some minute nuance of how I'm wrong, and get into a pissing match over who's right, do the community a favor and just PM me.
