USB host mode without VBUS?

[robertaden]

Hi.

I'm implementing a product based on an i.MX6ull SOM. On our board we will use a USB device operating on 3.3V. However, it seems like the USB bus does't work in host mode without 5V attached to the VBUS pin(s).

I would like to avoid implementing a 5V supply just to get USB working. So my question is, is there anyway to make the USB bus(es) work without it?

#imx6ul #usb ldo‌#usb vbus‌

[robertaden]

Hi,

I have read the datasheet and have no problems understanding the voltage range requirements for the VBUS. My question is if I need VBUS at all when running imx6ull USB in host mode. The device I will communicate with (on the same PCB) is operated on 3.3V and I don't have 5V available at all.

I would like to avoid adding a 5V regulator on the board just to trigger the VBUS signal.

I have used VBUS-less design with several other SOMs without any problem and was hoping to do so now as well.

[Yuri]

Hello,

  To be fully on safe side:  

when using i.MX6 USB, i.MX6 USB_OTGx_VBUS  must be applied and should be in range  4.40 V -  5.5 V.

Regards,

Yuri.

[robertaden]

Yes, to be totally safe I realize that just adding the 5V regulator and supply 5V to the VBUS is the way to go. I already verified that this work.

My question was if the 5V VBUS is necessary in host mode. I have NO need for 5V for anything else so adding a regulator just to trigger some register in the CPU is something I like to avoid if possible. The product will be battery operated so every milliwatt in extra power consumption will reduce operation time. Right now I'm down to less than 50mW total consumption which makes another regulator and the power loss that comes with it a big deal.

So, are you 100% sure that there is no way to enable USB host mode on the i.mx6ul without 5V VBUS attached?

[art]

Yes, to make the i.MX6ULL USB OTG port operate in the Host mode, the 5V VBUS voltage must be surely always present.

Best Regards,

Artur

[Yuri]

Hello,

  We cannot guarantee i.MX6 USB operation if USB_OTGx_VBUS is out of the specs.

Regards,

Yuri.

[Yuri]

Hello,

  According to table "Operating Ranges" in i.MX 6ULL Datasheet(s)

USB_OTGx_VBUS  should be in range  4.40 V -  5.5 V.

  The USB 2 specs provides the same requirements: 4.40 - 5.25 V

https://www.usb.org/sites/default/files/usb_20_20181221.zip 

Have a great day,
Yuri

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