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Mobile phones with USB OTG are not uncommon today. I am wondering that how can a battery operated device like mobile phone power a pen drive? From what I know, the power consumption of pen drive on 5V VBUS is around 100mA. The 5V can be derived from the battery voltage using boost converters, but are these converters so efficient and offer such a high current?

This question came to my mind when I came across a topic "connecting a pen drive to my android phone" when browsing for USB OTG.

Any thoughts?

Thank you.

LoveEnigma
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2 Answers2

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That 100ma rating is a maximum, not the normal rating. The pen drive is mostly idle, and should only need to peak occasionally. USB power can support at least 150ma, generally more.

http://en.wikipedia.org/wiki/USB#Power

Connecting a device that draws more power is most likely to flatten batteries sooner, but if it is within the USB power specifications, the phone should support it.

That said - I am not familiar with the specific limitations of OTG.

Danny Staple
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  • Thanks Danny for the answer. I agree that pen drives do not consume 100mA continuous current, but it does peak near 100mA for some and over 100mA for others. 150mA is the power supported USB 3.0 for low-power devices, whereas it is 100mA for USB 2.0. I think I should have mentioned that I am talking about USB 2.0. So, if I had to connect a pen drive to a product which has USB2.0 OTG (microAB) connector, I would have to support at least 100mA of output current. But from what I have seen in my extensive research, there is no IC which delivers more than 50mA AND supports all the OTG protocols. – LoveEnigma Apr 17 '14 at 10:43
  • One more thing is that I have not seen any smartphone in the market, even today, that has a micro-AB connector. They all have at the most a micro-B connector and still claim to have OTG support which is something I don't understand. – LoveEnigma Apr 17 '14 at 10:50
  • They have an aftermarket in micro-b to A connector for these. – Danny Staple Apr 22 '14 at 09:28
  • But that does not make it an OTG (dual role) device. When a mobile has micro-B connector on it, it is (has to be) simply a USB "device" with a micro connector rather than a standard-B connector; just a matter of form factor of USB connector. And you cannot connect pen-drive to a mobile having micro-B port. – LoveEnigma Apr 22 '14 at 12:30
  • Standards may say so - but I have such an adaptor - http://www.amazon.co.uk/gp/product/B00H4UHWZA. It does connect to devices like drives and similar. – Danny Staple Apr 22 '14 at 20:10
  • Yes, even I have a similar adapter, but do not have a phone which has micro-AB connector and hence I can't use it. If you don't mind telling, what phone do you have? I assume you are using that cable with your mobile phone. – LoveEnigma Apr 23 '14 at 04:13
  • I have a Samsung S3. This guy is showing stuff he's done with it - https://www.youtube.com/watch?v=46IiRyigUH0. – Danny Staple Apr 23 '14 at 07:44
  • Ahh, I see. Thanks. Seems like high end phones and tablets do have OTG in them. – LoveEnigma Apr 23 '14 at 12:17
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USB OTG is only possible on Micro or Mini USB connectors. The ID pin is shorted to ground on the host side in the host mode adapter cable. It is unconnected on the side of the pen drive (usually because a desktop USB connection is there with only 4 pins.)

Internally on the host device, 5V is produced with a boost converter from the power chips "common" bus. This is sometimes used for internal things, like driving the speaker amp to get the highest power when needed. Yes, boost converters can go from the typical Lithium cell of 3.7-4.2V up to 5V with very high current if needed. Efficiencies vary, but often close to 90%.

There is no requirement to use a micro-A or micro-AB connector for host mode, although the USB standard is that if it is a permanent host mode port, the micro-A connector should be used to distinguish it. The only thing required electrically to activate a host mode port is shorting ID pin to ground (if the device supports it).

Joe
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  • Thanks Joe for your detailed answer. Yes, I do understand the general architecture of USB and USB OTG. Actually, I am not able to understand that why many mobile phones say that they support OTG while they just have the micro-B connector on them? Do you know of any phone that has a micro-AB connector? Okay, so regarding power delivery with high current, I think a dedicated boost circuit is required. But then for data and protocol, they would need a separate IC for OTG control or a uC with fully integrated OTG PHY. Just thinking of the internal architecture of a OTG compliant device... – LoveEnigma Apr 18 '14 at 04:53