S69 USB1 series termination

[manuela_mendez]

Hello,

In S69-EVK schematics, 33 ohm series resistors are included only for USB0 but not for USB1. In a previous response NXP recommended it for both; Could you clarify why USB1 does not have it in the schematic and when it is needed?

Thank you

[diego_charles · Accepted solution]

Hi @manuela_mendez 

Thank you for your patience, just kindly continuing the thread for my colleague Pavel, and the one from our previous response

The LPC55s69 contains two USB interfaces:

-USB0 supporting Full-speed USB

-USB1 supportting High Speed USB.

Therefore:

-The full-speed USB (USB0)needs the 33ohms . 

The high-speed USB (USB1) connection is made through a shielded, twisted pair cable with a differential characteristic impedance of 90 Ω. In addition the USB1 is connected to the  internal USB 2.0 PHY, this will  do the impedance matching if necessary, therefore no external resistors are necessary. You can find more information regarding the electrical specifications for the USB high speed by downloading the USB 2.0 Specification.

We hope this could help you!

Diego

[manuela_mendez]

Hi Diego,

Thank you for the response. Impedance matched USB cable is common to both USB0/USB1 cases so I suggest we leave that out of the discussion. Your response seems to indicate that USB1 controller on the chip is already impedance matched to 90ohm so it does not need series termination unlike USB0. Is this the correct interpretation?

Thank you!

[diego_charles]

Hi @manuela_mendez 

My apologies for the delayed response, I agree with your understanding.

Diego

[manuela_mendez]

Thanks Diego!

[Pavel_Hernandez]

Hello, my name is Pavel, and I will be supporting your case, let me get more details.

Best regards,
Pavel