LayerscapeのトピックLS1046A USB Controller VBUS requirements

LS1046A USB Controller VBUS requirements

jlt1 — Thu, 18 Jun 2020 14:00:14 GMT

Hi,

I'm currently designing a PCB using an LS1046A, and wish to use the USB controllers.

I'm trying to figure out how to connect the VBUS pins on the controllers.The devices I am communicating with do not require a VBUS connection, just the data lines. I also do not have a 5V supply currently on my PCB, so I would have to place down a supply just for this VBUS connection. It seems unusual that a 5V supply is required in addition to the 3V3 and 1V0 USB supplies.

I think that connection is required but I can't find much documentation on this. The datasheet doesn't give requirements for the VBUS pins. AN5252 Table 22 says that connection is compulsory and the pins have a voltage range of "0-5.25V", but does not give an estimated current draw.

The LS1046ARDB schematic appears to connect the USB_3 VBUS to USB_P2_PWR, but this net is not powered (pin C1 of U3 is tied low). Does this mean that the USB3 bus is non functional on LS1046ARDB?

Are the VBUS pins compulsory for operation of the USB busses? if so, how much current do they draw? And are there any sequencing requirements for this power supply?

Re: LS1046A USB Controller VBUS requirements

ufedor — Thu, 18 Jun 2020 16:23:15 GMT

> Are the VBUS pins compulsory for operation of the USB busses?

Yes.

> if so, how much current do they draw?

The current is negligibly small.

> And are there any sequencing requirements for this power supply?

No.

> pin C1 of U3 is tied low

USB2_PWREN is controlled by U8.

Re: LS1046A USB Controller VBUS requirements

jlt1 — Thu, 18 Jun 2020 16:30:45 GMT

Thanks very much for the prompt reply ufedor!

> USB2_PWREN is controlled by U8.

Oops, not sure how I missed that IC, sorry!

>The current is negligibly small.

Negligibly small being <5mA? Just asking to see if it is feasible to use an LDO from my input rail, without burning too much power.

Re: LS1046A USB Controller VBUS requirements

ufedor — Thu, 18 Jun 2020 16:38:22 GMT

> Negligibly small being <5mA?

<50uA

Re: LS1046A USB Controller VBUS requirements

spoulin — Tue, 08 Sep 2020 19:15:14 GMT

Hi @ufedor

Is it mandatory to feed that pin with 5V ? or 3.3V would be ok ?

What is the use of this pin for the LS1046 internally ?

What is the VIH of this pin ?

Thanks in advance !

Re: LS1046A USB Controller VBUS requirements

ufedor — Wed, 09 Sep 2020 02:53:21 GMT

The nominal voltage for this pin is 5 V.

There is an internal comparator; if VBUS drops below about 4.4v, an over-current is signaled and the port is shut down.

Re: LS1046A USB Controller VBUS requirements

spoulin — Mon, 21 Sep 2020 14:56:14 GMT

Thanks Ufedor, it is appreciated.

Regards !

Sylvain

Re: LS1046A USB Controller VBUS requirements

jimmy_zhao — Fri, 02 Jun 2023 15:45:19 GMT

When USB is configured as a USB host, VBUS pin is not used. It is only used when USB is configured as USB device. Connect a 3.3V to VBUS should work even it is configured as a USB device.