USB C audio board

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nico
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USB C audio board

Postby nico » Sat Dec 16, 2017 5:26 pm

Hi,

I would like to add a USB C connector to a futur product based on xCORE-200 Multichannel Audio Platform.
Any special thoughts or wiring tips ? That will be the first time that I use this type of connector ...
I will keep the 3 way hub that is on the dev kit design.

Thanks,
Regards,
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mon2
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Postby mon2 » Wed Dec 20, 2017 12:47 pm

Hi nico. We reviewed USB Type C about 2 years ago for a few months and back then there was a lot of chaos as we reviewed many non-compliant cables for power delivery. Reported a lot of our findings to silicon vendors and believe that the issues we observed have been fixed. Do not believe you are concerned about power delivery but more on signal integrity of this reversible connector.

This is a quick summary as there is a lot of good info on the net.

The XMOS IP is USB 2.0 based so you should prepare to support upto USB 2.0 HS (480 Mbps). Be sure to include support for ESD protection and in-rush current on the VBUS rail. This is required for all USB designs and numerous developers have reported damage to their XMOS devices without such protection.

On the USB Type C connector, there are 2 sets of mating pins - one layer on the type side of a blade and another copy on the bottom side. You can safely ignore the USB SS pins (Superspeed signal lines since you are not working with SS = USB 3.0 / USB 3.1 Gen 1 interface).


Image

The signals marked in RED are of interest to your project.

Most articles on the net are just shorting D+ (top) to D+ (bottom) and respectively D- (top) to D- (bottom) and then feeding this single pair of signal lines to their downstream USB device with impedance controlled traces of 90 ohms. This solution may be sufficient for your project but will require thorough testing of the final design.

Microchip is noting that this does impact the signal integrity of the USB 2.0 signals. Reference:

http://ww1.microchip.com/downloads/en/A ... 01914B.pdf

We believe that a more elegant solution to improve the above interface is to insert a USB 2.0 signal mux. This mux will accept in signals from the top and bottom sides of the blade and then switch the mux based on the orientation of the USB connector. See Figure 4 in the above document. The detection of the connector orientation can get complex but believe that there are now single chip solutions for this purpose. Diodes Inc. mentions one but no datasheet - perhaps will release with a request to your local FAE.

https://www.diodes.com/products/connect ... 5USB30216A
* using this component + USB 2.0 signal mux = guaranteed solution but at an added expense

Recently, Cypress (who also has been working on assorted USB Type C solutions - early versions were not to spec when we did our initial review - assuming they have fixed the raised issues by now), check out their PSOC6 kit schematics which makes use of this same connector:

http://www.cypress.com/documentation/de ... ioneer-kit

Taken from their schematics:

Image

They have also just shorted the USB 2.0 signals for their use and without an external mux. We recommend that C85 be 250+ volts. See Johanson caps @ 500v from Mouser:

https://www.mouser.com/Search/Refine.as ... +capacitor

Summary: Most of the industry is just shorting the top & bottom USB 2.0 signals and using in their design. This may be fine for the high speed signals on the XMOS IP but do pay attention to the USB 2.0 impedance controlled traces @ 90 ohms (be sure to inform your PCB shop of where these traces are on your design). Request for your PCB shop to verify these PCB traces are compliant by supplying a TDR test documentation. 4L PCB design is high recommended. ESD protection + in-rush protection is mandatory. Consider the low cost AP2331 for the in-rush protection on the VBUS rail.

https://www.diodes.com/assets/Datasheets/AP2331.pdf
* do confirm if the hold current is ample for your project - Diodes Inc. also offers higher current versions of this component

update

Also a few words on the USB Type C connector. To get started, consider to use a reliable brand through Digikey / Mouser. You can review offshore brands later once your widget is a hit. We are speaking from some experience on offshore sourcing where we met with a manufacturer of USB mini connectors and after ordering their MOQ of 2 T&R, the parts were found to be quite loose in our opinion. We did not want to use for our production. After some chatter between our companies, the CEO of this supplier requested the spec for the mating tension which we hijacked off a datasheet from Digikey. They rebuilt the parts and shipped to us in Canada at their expense. The next batch was ideal but we lost faith in the vendor. The savings were minimal after this exercise with this specific vendor. Recently sourced additional parts from a different source and they have been great for a medical product we recently sampled. Even though it may be expensive, start with local suppliers and consider to receive samples from offshore vendors before assuming that all connectors are created equal.

Be sure to check on the footprints and other physical details to be sure that you are not stuck with a single vendor or manufacturer for the connectors.

Here are the contact details of a vendor we have used in a few projects with excellent results:

http://www.homyet.com/en/products/cid_214.html

Seven Zhang /+86 15112386375
SHEN ZHEN HOMYET PARTS ELECTRONICS CO.,LTD
Tel:+86-755-83676824 29768399
Fax:+86-755-83676835 27888655
Add:306,E Building ,HuaChuangDa Industrial Park,Bao'an 42 District,Shenzhen , Guangdong Province,CHINA
Mail:seven@homyet.com
Web:www.homyet.com http://www.homyetparts.com
QQ: 2355400604 Skype: sevenzhang07@hotmail.com
HONG KONG HOMYET PARTS ELECTRONICS CO.,LTD
Add:Unit 04, 7/F,Bright Way Tower, No.33 Mong Kok Rd, Kowloon, Hong Kong
Tel:00852--23892981
Fax:00852--35902333




Kumar
nico
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Postby nico » Wed Dec 20, 2017 6:33 pm

Thanks a lot mon2 for this detailed answer that I need to study !

Regards,
Nicolas
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JPS64
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Postby JPS64 » Tue Jan 16, 2018 8:53 pm

Hello,

here another vendor (STEP, EAGLE, ALTIUM symbols available).

http://katalog.we-online.de/de/em/COM_3 ... 05c8fc333b

JP
RitchRock
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Postby RitchRock » Fri Feb 16, 2018 2:57 am

Hi,

For the configuration channel logic when using usb 2.0 over USB type C, would you suggest the use of a part like the TUSB320? Could this also be done by just using a pull down resistor?

Any other considerations?

Thank you very much for the info on signal integrity.
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mon2
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Postby mon2 » Fri Feb 16, 2018 11:30 am

Hi. If you can justify the expense, apply a USB 2.0 mux as mentioned in the above document from Microchip for best signal integrity. Then allow for steering of this mux using TI TUSB321 or similar. This part features a pin for the mux steering.

See 2.3.2.1 of the same document on how the cable orientation works.

Low cost method is to just just short top & bottom D+ / D- signals together and then no mux is required. This what most designers are doing to save on costs.
RitchRock
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Postby RitchRock » Fri Feb 16, 2018 4:56 pm

That makes sense for the using the mux. Say, I decide to go low-cost route, can I just use resistors on the CC lines to enumerate at 500ma or is some sort of controller like the TUSB320 necessary? I noticed on page 27 of the the TUSB320 datasheet, TI recommends to keep the stubs less than 3.5mm when shorting D+/D-.
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mon2
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Postby mon2 » Fri Feb 16, 2018 5:25 pm

You are not using PD which is a complex handshake between the downstream (DFP) and upstream (UFP) powers and involves typically using a local micro to receive and interpret power contracts.

Download the latest USB Type C specs here:

http://www.usb.org/developers/docs/

http://www.usb.org/developers/docs/usb_32_020718.zip

There are a number of permutations available and you must decide if your widget will be using a cable or will it be docking directly into the host PC (ie. the cable is fixed to your widget and terminates with a USB Type C connector). Based on your selection, you must then follow the specification outlined in the above download to be sure the product will work correctly.

Believe you are interesting in a USB Type C support on your dongle and then will use a cable to convert to standard USB 3.1 Type A connector? If yes, then you must source such a cable which requires that Rd @ 56k. See Table 3-12 & 3-13 inside the above download (USB Type-C Cable and Connector Specification July 14, 2017). Be sure to double check your work before starting as it has been a while since we reviewed this interface. Being that you are only after 500mA on USB 2.0 or 900mA on USB 3.1 Gen1 connectors which is default, you are NOT dealing with PD in this project. PD is for power sucking projects that may demand upto 100W of power and demands the use of E-marked cables which is another mess in itself. Hoping that leg of the industry has improved now than when we did our first review. Either way, the above download fileset is your Bible for USB Type C specification.


Image
RitchRock
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Postby RitchRock » Fri Feb 16, 2018 10:56 pm

Just to follow-up - In section 4.5.1.1 of the USB Spec document you referenced, it states that "In the case of USB 2.0, this is done by shorting together the two D+ signal pins and the two D− signal pins in the host and device receptacles." So even the USB Spec is saying this is acceptable.

Further research shows that it seems to be quite acceptable to use two 5.1K resistors to ground from the CC lines. Of course, cables that meet spec and keeping the stubs short when doing the PCB routing is important, but that appears to be it for USB 2.0 over a USB C connector.

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