USB on LPC54016JET100 with Vdd=1.8V

[andrewsglenn]

We'd like to use the LPC54S016JET100 with Vdd=1.8V to interface with all our 1.8V peripherals.

Looking at the LPC540xx data sheet Table 12, minimum Vdd for USB Full Speed is 3.0V, but for High Speed is 1.71V, implying we should use USB1 for our interface.

My question is what happens if a Full-Speed device is connected to the High-Speed interface? Does it fail to enumerate as it needs a higher voltage? 

What are the limitations of trying to use USB1 at 1.8V?

[Alice_Yang]

Hello @andrewsglenn 

1> "My question is what happens if a Full-Speed device is connected to the High-Speed interface? Does it fail to enumerate as it needs a higher voltage? "

->> My understanding is that, for the working voltage of USB0( Full- speed) is 3.0 -3.6v.

The working voltage of usb1 is 1.71 - 3.6V.

2> "What are the limitations of trying to use USB1 at 1.8V?"

->> I.8v is the normal voltage limits.

BR

Alice

[andrewsglenn]

So if you're using USB1 and it is connected in Full Speed mode rather than High Speed (due to limitations of the device connected) It will still work at Full Speed?

[Alice_Yang]

Hello @andrewsglenn 

Yes, it will work as full speed.

And for Full Speed operation, VDD must be min of 3V. 

BR

Alice

[andrewsglenn]

Here's our setup:

VDD is 1.8V

USB1_AVDDC3V3 is 3.3V

USB1_AVDDTX3V3 is 3.3V

From what you are saying, USB1 will work as a High-Speed device, but will fail as a Full-Speed device because VDD is not 3V or higher?

Is this correct?

[Alice_Yang]

Hello @andrewsglenn 

If USB1 works as Full- speed device, 

VDD is 1.8V

USB1_AVDDC3V3 is 3.3V

USB1_AVDDTX3V3 is 3.3V

Yes, USB1, will work.

BR

Alice

[Alice_Yang]

Hello @andrewsglenn 

There is a little bit confusing and sorry about this, I will confirm with our internal.

BR

Alice

[andrewsglenn]

Any luck finding a definitive answer?

[Alice_Yang]

Hello @andrewsglenn 

Please see my reply last  time:

BR

Alice

[andrewsglenn]

Thank you.