Can the active USB signals be applied to the TUSB2036 IC hub ports (upstream, downstream) when it is not powered.

Radosvet B.

Intellectual 490 points

Other Parts Discussed in Thread: TUSB2036

Hello!

Can the active USB signals be applied to the TUSB2036 IC hub ports (upstream, downstream) when it is not powered.

The IC reliability and/or USB device output will be jeopardized in this case?

Regards,

R. B.

over 8 years ago

0 Elias Villegas M. over 8 years ago

TI__Guru* 76130 points

Hello,
I will ask to the designer whether these terminals are fail-safe, however, such a condition is not allowed in USB and it will never happen in a USB compliant environment.
Regards

0 Radosvet B. over 8 years ago in reply to Elias Villegas M.

Intellectual 490 points

OK.

In the application described (https://e2e.ti.com/support/interface/usb/f/1008/t/507688 ) the MCU can switch off the TUSB2036 IC hub and the multimedia devices power supply voltages when the whole system is switched off.

The MCU is always powered from the battery or wall-adapter.

1. Are there problems possible in this circuitry like “unpowered IC hub and powered MCU connected with the USB lines together”?

Should I protect the IC hub and the MCU, and how?

2. The iPhone can be powered and the system (i.e. and the IC hub) – not.

Such a situation can bring reliability problems?

But unpowered PC USB peripherials (printers, etc.) connected to a powered PC do not die practically?

Ii is not true?

Regards,

R. B.

0 Elias Villegas M. over 8 years ago in reply to Radosvet B.

TI__Guru* 76130 points

Hello,
Unpowered USB devices will be powered-up via VBUS once the USB cable is attached.
I talked with the designer and the TUSB2036 upstream DP/DM lines are not fail-safe, so you can't apply voltage to this terminals when the Hub is not powered.
If you are going to share USB connection you need a USB switch, you can find one at the link below.
Regards

www.ti.com/.../ts3usb221

0 Radosvet B. over 8 years ago in reply to Elias Villegas M.

Intellectual 490 points

It does mean that I should use an USB switch on the IC hub upstream input (between an iDevice and the hub) too?

The application described (https://e2e.ti.com/support/interface/usb/f/1008/t/507688 ) is self-powered.

iPhone/iPad permits a USB maximum current consumption of around 5mA in software (http://blog.jdslabs.com/?cat=57 ).

*Unpowered USB devices will be powered-up via VBUS once the USB cable is attached.*

This is about bus-powered devices only?

Regards,

R. B.

0 Elias Villegas M. over 8 years ago in reply to Radosvet B.

TI__Guru* 76130 points

Hello,
I've just realized the two E2E posts are the same.
The implementation you describe in the link in which both the MCU and the iDevice can act as a Host requires both devices to be OTG, USB Hubs does not support OTG.
If the only one that will be a USB Host is the iDevice and the MCU will provide power to the TUSB2036's downstream DP/DM then you will need a switch between the MCU and the TUSB2036's downstream, note that the scenario in which the MCU provides power upstream is a non-compliant USB scenario.

Regards

0 Radosvet B. over 8 years ago in reply to Elias Villegas M.

Intellectual 490 points

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Can the active USB signals be applied to the TUSB2036 IC hub ports (upstream, downstream) when it is not powered.