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Benson Leung
15,466 followers -
Fixer of Bugs.
Fixer of Bugs.

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How do USB Type-C chargers support older USB devices?

tl;dr: All new USB-C dedicated chargers must also support USB Battery Charging 1.2 Dedicated Charging Port (BC 1.2 DCP) by shorting together Dp and Dn.

Ever run into a situation where you plug your older MicroB or Lightning port phone into a Type-C charger and nothing happens, or slow charging happens?

I was looking through some of the ECNs (Engineering Change Notices, or how the folks behind USB make changes to the specs) in the latest USB document bundle, and I noticed a document named, "USB Type-C ECN BC1.2 Clarification."

In red, there's the new requirement:
"A USB-based charger with a USB Type-C receptacle (Source) which is not capable of data
communication shall advertise Type-C current of at least 1.5A and shall short D+ and D- together
with a resistance less than 200ohms. This will ensure backwards compatibility with legacy sinks which
may use BC1.2 for charger detection."

Why did they make this change? Because prior to this requirement, BC 1.2 was completely optional and some dedicated chargers with Type-C receptacles chose to not implement it, instead implementing Apple's 2.4A BrickID, or nothing at all (floating Dp Dn). In some cases, this meant that completely valid cable combinations (using a C-to-Areceptacle adapter + A-to-B or A-to-Lightning, or using a C-to-uB, or a C-to-Lightning) would result in no charging or slow charging.

Going forward, all new dedicated chargers (those that lack any data functionality) must short Dp and Dn in accordance to BC 1.2 DCP. This will ensure that legacy devices will detect Type-C chargers as DCPs. This will include legacy iPhones and iPads as well.

Note: This requirement also means that it's no longer allowed to use Apple's BrickID method on Type-C receptacles anymore to advertise 2.4A on the port. This was covered in an earlier Type-C ECN which forbid all proprietary charging methods on the new Type-C connector, including Apple's. Now, if it's a receptacle dedicated charger, it MUST support BC 1.2 DCP.

This ECN, by the way, has also been rolled into the latest Universal Serial Bus
Type-C Cable and Connector Specification Revision 1.3.


+Nathan K. and +Hanpen for FYI, since they both ran into chargers that don't do this yet (various Anker and other chargers).
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Apple's new iPhone 8 and iPhone X implement USB Power Delivery over Lightning, very similar to the iPad Pro 12.9" and 10.1" for high voltage charging.

While this means that the phones themselves won't have USB Type-C ports, with the right C-to-Lightning cable, you'll be able to use them with the same power sources that charge laptops and other Type-C devices such as Pixel phones.

Definitely progress. :)
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How do Type-C Power Sources and Power Sinks dynamically negotiate power? (What are Sink Power Sub-States?)

If you recall my blog post on USB Type-C’s Configuration Channel (ref 1), one of the features of CC is to allow the power source to advertise its power capabilities to the sink; the source uses three values of the Rp resistor (Default USB, 1.5A, 3.0A) to indicate how much current the Type-C power sink may draw at 5V, and the sink detects this as different voltage levels on its CC pin on its end of the cable.

An important detail that I hinted at is that the source is allowed to dynamically change the value of Rp used during the same session without disconnecting, and the power sink must respond in kind and adjust its current limit.

The part of the USB Type-C spec that governs the behavior is Section 4.5.2.3 “Sink Power Sub-State Requirements” and the simple state diagram attached to this post. When a device is in Power3.0.SNK state, it may draw no more than 3.0A at 5V. When a device is in Power1.5.SNK state, it may draw no more than 1.5A at 5V.

There are several reasons that a power source may change the power advertisement during the duration of a Type-C session.
The source may do this for load balancing (ie, the power source has a shared pool of power that must be split unevenly between several ports), or for temperature mitigation, for example. Some condition may change, causing the port to need to reduce the power consumption on a port, or allow the power consumption to jump up to a higher level.

Some examples of real-world power sources that change their Rp:
1) Google’s 22.5W Dual Port charger (https://store.google.com/us/product/usb_c_dual_port_charger?hl=en-US)
This Google charger has a 22.5W budget and two Type-C ports. Each port, individually, is capable of 3A, but when two devices are plugged in, one port gets 3A and the other gets 1.5A
2) Samsung Chromebook Plus (Ref 2) - This Chromebook is designed for 15W total output balanced between two Type-C ports. When a single one of the laptop’s Type-C ports is being used as a source, that device is given a 3.0A advertisement. When both are used, 1.5A advertisements are given to both ports.
3) Apple’s MacBook Pro 13” and 15”. (Ref 3) - Apple’s MacBook Pro has either 2 or 4 Type-C ports, with support for 15W output on half of the ports and 7.5W output on the other half.


In the case of the Google 22.5W Dual Port charger, the power advertisement of each port is based on measured power consumption. If the sink attached to the charger’s bottom port draws more than 1.4A, the charger will allow it to have up to 3.0A via the 10kOhm Rp, while the top port will only get 1.5A via 22kOhm Rp. However, if the power consumption drops below 1.4A again, the top port will see 3.0A given to it. This allows for smarter balancing of two devices when one’s battery gets close to topped off and it naturally draws less current, for example.

One important detail about the transitions between Sink Power Sub-States is that there is actually a deadline in the spec on some of the transitions. Crucially, transitions from higher to lower sub states, for example from 3.0A -> 1.5A are limited to tSinkAdj, which is mandated to be 60ms in the spec. Within 60ms of the voltage dropping from vRd-3.0A range to vRd-1.5A range, the sink (phone, laptop, etc being charged) must lower its power consumption to within the new limit.

Hope this has been helpful in understanding how dynamic power balancing happens in USB Type-C!

Ref 1 : https://plus.google.com/+BensonLeung/posts/4xq4EDjXMw8
Ref 2 : http://www.samsung.com/us/computing/chromebooks/12-14/xe513c24-k01us-xe513c24-k01us/
Ref 3 : https://support.apple.com/en-us/HT207256


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8/28/17
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The USB 3.0 Promoter Group has announced that the next version of the USB Specification is coming soon: USB 3.2

It promises a doubling of the data rate of USB 3.1, with Gen 1 cables doubling speed from 5gbps to 10gbps, and Gen 2 cables doubling from 10gbps to 20gbps.

The basic premise of USB 3.2 is fairly simple: A Full-Featured USB Type-C cable has 15 wires, 8 of which are SuperSpeed wires. When operating in USB 3.1 Gen 1 or Gen 2 modes, only 4 of those wires are used right now. The other 4 may be assigned to an Alternate Mode like DisplayPort, but when used for USB-only operations, they are dormant.

USB 3.2 will double the bandwidth by using all 8 wires for USB in cases where both sides can support it and aren't using the other 4 wires for an alternate mode.

http://www.businesswire.com/news/home/20170725005509/en/USB-3.0-Promoter-Group-Announces-USB-3.2

#USB #TypeC #USB3.2 #USBC
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Only tangentially related to USB, but it is a story about collaboration between otherwise fierce competitors, and how it could go wrong...
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I've posted a review of IOGEAR's Gen 2 100W C-to-C cable:
https://www.amazon.com/review/R3I108G87O0H2N/ref=cm_cr_rdp_perm

tl;dr: Excellent USB 3.1 Gen 2 Type-C cable. Supports 100W and 10gbps operation.

This cable's another Full-Featured USB Type-C cable, but also has 5A support, which is important for >60W power supplies and power sinks, such as the new MacBook Pro. All the wires are here on this one, and it works for DisplayPort Alt Mode well at 4k60.

Also, good use of the official USB logos on both the cable and prominently on the box.

#USB #TypeC #USBC
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5/23/17
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+Samsung USA  and my team, the +Google Chrome OS team , has collaborated on the Samsung Chromebook Pro, which is about to go on sale on May 28th.

This convertible laptop has two #USB   #TypeC   ports for charging and power delivery, USB 3.1 Gen 1 data, and DP Alternate Mode! Its Type-C and PD support is based on Google's Intel Skylake-Y reference implementation.

I've been using this Chromebook for a little while, and it's a good one.

#USBC  
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I've done a #USB   #TypeC  cable review. Aukey's CB-D36 USB 3.1 cable.
tl;dr: Bad cable. Missing 6 data wires. Missing e-marker. Won't work for video out.

(NOTE: This cable is similar to the CB-CD8 I reviewed a few days ago. It's safe to assume that Aukey has made this error on all of their "Fully-Featured" USB 3.1/3.0 C-to-C cables)

This cable claimed to be a USB 3.1 cable, but upon closer inspection, it has a bunch of serious problems. It's 6 wires short of being a true USB Full Featured cable, meaning it fails to support Alternate Modes that take advantage of ALL of the wires in the cable, for example, using DP Alternate Mode to display 4k60 video.

What likely happened here is that Aukey designed a decent A-to-C USB 3.1 cable and decided to make it a C-to-C cable by swapping the A plug for a C plug. They didn't read the spec on the section that describes that cable, which would have told them that they needed to design the cable with 15 wires through, not 9.

Aukey didn't read the spec, but I did. Bad cable.

It also fails signal integrity tests at 10gbps, so Aukey's claim that this is a USB 3.1 Gen 2 cable is flatly false advertising.

Also, the cable is missing an e-marker chip, and is missing proper USB logos to top it off.

I'll be contacting Aukey, and try to pursuade them to pull the cable, destroy their inventory, and offer refunds to every customer they sold one of these to...

#USBC  
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I've done a #USB   #TypeC  cable review. Aukey's CB-CD7 USB 3.0 cable.
tl;dr: Bad cable. Missing 6 data wires. Missing e-marker. Won't work for video out.

(NOTE: This cable is practicaly identical to the CB-CD8 I reviewed a few days ago. It's safe to assume that Aukey has made this error on all of their "Fully-Featured" USB 3.1/3.0 C-to-C cables)

This cable claimed to be a USB 3.0 cable, but upon closer inspection, it has a bunch of serious problems. It's 6 wires short of being a true USB Full Featured cable, meaning it fails to support Alternate Modes that take advantage of ALL of the wires in the cable, for example, using DP Alternate Mode to display 4k60 video.

What likely happened here is that Aukey designed a decent A-to-C USB 3.1 cable and decided to make it a C-to-C cable by swapping the A plug for a C plug. They didn't read the spec on the section that describes that cable, which would have told them that they needed to design the cable with 15 wires through, not 9.

Aukey didn't read the spec, but I did. Bad cable.

Also, the cable is missing an e-marker chip, and is missing proper USB logos to top it off.

I'll be contacting Aukey, and try to pursuade them to pull the cable, destroy their inventory, and offer refunds to every customer they sold one of these to...

#USBC  
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Here's another of the same kind of #USB   #TypeC  adapters.
tl;dr: Bad charger. Won't work with e-marked cables.

Yet another clone of the BOLWEO, Soulbay, iVAPO, and HOOKE chargers. Avoid whoever this common supplier is...

#USBC  
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