IMX6UL USB to UART has Level shifter is it require?

[ramesh6663]

In IMX6UL reference design USB to UART circuit has 2 bit Level shifter and the notes mentioned "Level-Shifter to insure no IO backfeed".

Q1. What is mean by " Level-Shifter to insure no IO backfeed" ? 

Q2. Do we require Level shifter, If i connect UART Tx,Rx lines directly to IMX6UL processor pins what will happen?

As per my understanding USB to UART chip CP2102 has powered by USB cable at any time from different power source (Example : Laptop). so we need to makesure when the communication need to be happen and when its not so we are enable and disable 2bit level shifter accordingly. Is it correct?

Please see below snap-shot.

[art]

Yes, the level shifter is required since the CP2102 USB-UART bridge and the UART section of the processor are powered from different power supplies. The UART signals of CP2102 are in the VUSB_UART_3V3 power domain that is internally produced by CP2102 from the VBUS voltage, coming from the USB connector, whereas the UART section of the processor is powered from the on-board DCDC_3V3 power supply. Moreover, the VUSB_UART_3V3 power is present only when the CP2102 USB-UART bridge is conencted to an external USB Host. So, the level shifter is required to maintain the signal integrity and avoid the signal latchup.

Have a great day,
Artur

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[ramesh6663]

Dear Artur,

  Thanks for your quick reply. its very useful.

Thanks & Regards,

Rameshkumar

[ramesh6663]

Could you please any one help us for the above query?

Thanks & Regards,

Rameshkumar