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TUSB8042: Differential Impedance

Roy Hsu
Genius 9390 points
Part Number: TUSB8042

Hi Team,

The datasheet states that the differential pairs "Must be designed with a differential impedance of 90 Ω ±10%".

However, the CPU requires the differential impedance to be 85 Ω ±10% for USB3 and 100 Ω ±10% for USB2. Should I follow the instruction from the CPU vendor or TI?

Thanks!

Roy

  • 0
    TI__Guru 60870 points

    Hi Roy,

    The TUSB8042 was designed in accordance with the USB specification which states:

    The differential output impedance of a high-speed capable driver is required to be 90 Ω ±10%.  Likewise the USB 3.x spec follows similar guidelines.

    85 ohms is within 10% of 90 ohms so that should be fine.  Can you confirm with the CPU vendor that USB 2.0 requires 100 ohms, this is very unusual.  

    Regards,

    JMMN