TUSB2046I: Clarification required on USB Port Power Enable/Disable Behavior

Monisha M

Tool/software:

Dear Team,

We are working with the TUSB2046IBVF and TPS2062DGNR. We have observed that USB power to the downstream ports is enabled only when the upstream port is detected. However, the power remains enabled even after the upstream port is disconnected. Our expectation is that the port power should be disabled once the upstream port is removed. Could you please clarify how the port power is controlled or enabled/disabled in this case? Is it possible to disable the downstream port power when the upstream port is disconnected?

Best Regards,

Monisha M

4 months ago

0 Vishesh Pithadiya 4 months ago

TI__Mastermind 48721 points

Hi,

This seems to be an issue with self-powered vs. bus-powered modes.

In self-powered mode the hub is sourced with power from an external source and will supply Vbus to the downstream ports independently of the upstream connection.

In bus-powered mode the hub is powered by the upstream connection, and power going to the DS port will be determined by the upstream connection.

0 Monisha M 4 months ago in reply to Vishesh Pithadiya

Prodigy 170 points

Hi Vishesh,

We are operating in self-powered mode. It is mentioned, in self-powered mode, VBUS is supplied to downstream ports independently of the upstream port. However, in our case, the downstream ports remains unpowered until the upstream is connected. Is this behavior expected in self-powered mode?

Best Regards,

Monisha M

0 Vishesh Pithadiya 4 months ago

TI__Mastermind 48721 points

Monisha M said:
the downstream ports remains unpowered until the upstream is connected.

Monisha M said:
We have observed that USB power to the downstream ports is enabled only when the upstream port is detected. However, the power remains enabled even after the upstream port is disconnected.

Is the power on the downstream ports when the upstream is connected, disconnected, or both?

0 Monisha M 4 months ago in reply to Vishesh Pithadiya

Prodigy 170 points

Hi Vishesh,

The power on the downstream port is enabled only when the upstream is connected and it remains enabled even when the upstream is disconnected. But to enable power on downstream the upstream needs to be connected at least once.

Best Regards,

Monisha M

0 Vishesh Pithadiya 4 months ago in reply to Monisha M

TI__Mastermind 48721 points

Hi,

I will reach out to our systems engineer and see if this is expected behavior.

I will also try to recreate this in lab, but most of our equipment is already in use so this may take 1-2 days.

0 Vishesh Pithadiya 4 months ago in reply to Vishesh Pithadiya

TI__Mastermind 48721 points

Also, what is the desired behavior here?

0 Monisha M 4 months ago in reply to Vishesh Pithadiya

Prodigy 170 points

Hi Vishesh,

We are expecting that the downstream port should be disabled if upstream is disabled (i.e., downstream port should always have a dependency with upstream port).

Best regards,

Monisha M

0 Vishesh Pithadiya 4 months ago in reply to Monisha M

TI__Mastermind 48721 points

Hi,

If that is the case, the best system implementation would be as bus-powered not self-powered.

0 Vishesh Pithadiya 4 months ago in reply to Vishesh Pithadiya

TI__Mastermind 48721 points

Hello,

Closing thread due to inactivity. If you have any follow-up questions or concerns, feel free to reply.

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TUSB2046I: Clarification required on USB Port Power Enable/Disable Behavior