USB C and OTG

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#1
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Hi guys,

 

Are there any USB C ninjas out there?

 

Are you aware of "USB micro-B to USB C OTG cables"?

 

I've been tasked with making a self powered USB 2.0 Device with a Type-C receptacle. Nothing special there, C supports USB 2.0 just fine, and it doesn't even need any electronics to compensate for the two insertion directions.

 

But my problem is this: To connect this C Device to a micro-A/B port (as in your Android phone) there will have to be a C to micro-B cable. So far so good. But how will the phone treat the Device as a Device? In other words, will the ID pin be grounded on the micro-B side of the cable? That is the way OTG cables are set up today, although they typically have a USB A receptacle in the other end, not a USB C plug.

 

My suspicion is that the ID pin will be left floating and thus make the phone a Device. That makes sense if you want to use a the C to micro-B cable to charge your phone from a modern computer. That is what looks like the case in this cable:

http://www.digikey.com/product-s...

 

I haven't yet come across cables which translate the CC pin logic of USB C to ID pin logic of USB micro and mini plugs. Are you aware of anything like this? Is there such a thing as an OTG cable from micro-B to Type C?

 

 

Thanks,

Borge

 

 

 

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It all starts with a mental vision.

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Thanks for the link!

 

I have looked further into the details in the last few days. The question I have boils down to how cables implement the ID pin on the micro B side and the CC pins on the C side.

The device in question is a self powered USB 2.0 product with a USB C receptacle. The host in question is any existing Android phone with a USB micro-A/B receptacle.

When the cable is plugged in, it (or the pulled-down CC pins in my device) must inform the host that ID is low. This is hardwired in OTG cables.

 

I hope to avoid having to bundle a custom USB micro-B to USB C cable with my product. That will lead to confusion. The only pinout I've seent his far looks like it has micro-B's ID and C's CC pins all floating.

 

Is it allowed / recommended / possible to short both CC pins and ID together? The pulled-down CC pins in my product would then correctly identify things as a device on the micro-B side of things.

 

Thanks,

Børge

 

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I do not know about this, but it seems wrong to have a product with a Type C port, that is only USB 2.0 compliant.

It all starts with a mental vision.

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It may seem wrong, but it is entirely allowed. It will not be hard to find products that are USB 2.0 devices with USB C receptacles.

 

I've been reading up a little on this over the last few days. This is what I have found this far.

 

Actually, the C plug is pretty smart. For USB 2.0 you don't need any muxes or direction detection logic because the USB C plug receptacle is rotationally symmetric. The thing which bugs me about it, though, is that there doesn't seem to be a generic cable from micro-A to C where the host-device direction can be arbitrary. I.e. you can't easily plug a C device to a micro-A/B host such as 99% of all Android phones.

 

The cable which would allow that would need to tie the ID pin in the micro-A plug to GND. Or micro-B for that matter. I'm a bit hazy on when you must use one and not the other. It would make more sense that the cable leading toward the device be a micro-B male.

 

 

Børge