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TUSB522P: TUSB522P pull-up/down resistor settings & potential impacts

Leo Chow
Expert 3120 points
Part Number: TUSB522P

Hi,

i'm working on a USB-C design which involves TUSB522P USB3.1 dual channel redriver & I noticed in a certain copy of reference designs the resistors used

1) All pull-up pull-down resistors were set to 47Kohm following the datasheet However, the test boar's typical design section. However looking into the EVM schematics, it seems to be using 1Kohm resistors instead? Which one should i take reference from? Our application uses 47Kohm for now & i would like to understand the implication of change in resistor values for my design.

2) All of our boards were working fine and passing the USB compliance test. This is the one unit that suddenly failed on only PORT 1 (RX). TX2 and RX2 ports are working, but marginally failing the eye-diagram TX test. Adjusting the OS1 and DE1 settings did not help much - so maybe TX1 also has some kind of malfunction?

3) The part was reworked and replaced with a good part and board system hub works fine again. Does this implies that i might be having a failed device here?

Regards,

Leo

  • 0
    TI__Guru 64326 points

    Hi,

    1)  The pull up and pull down values should be selected to match the high, mid and low voltage levels located in section 6.6 Electrical Characteristics, DC. There should be no impact as long as these voltage levels are meet. I would recommend using the 47kohm resistor so that you dissipate less power through the pull-up and pull-down resistors.

    2) Can you share the failing eye diagram? I assume there were no changes to the design when this part failed, is this correct?

    3) This does imply that this part may be damaged however we should confirm the schematic and application before concluding this. Can you share the schematic and describe the pre & post channel in this application? 

  • 0 in reply to Malik Barton57
    TI__Expert 3120 points

    Hi Malik,

    I'll need some time to obtain the eye diagram as customer is rushing on P2 build for their project. For schematic connection, it resembles the EVM schematic hence result should be pretty much the same. Also can you verify if TUSB522P is reversible? Meaning that it doesn't matter which side faces the device / host. Can you verify if my understanding on the following diagram was correct?

  • 0 in reply to Leo Chow
    TI__Guru 64326 points

    Hi,

    The eye diagram results will vary based on the layout of the PCB even if the schematics are very similar or the same. TUSB522P is reversible as long as the routing is correct.