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TUSB546-DCI: in ALT mode without USB3.1

Mark Valentijn
Prodigy 10 points
Part Number: TUSB546-DCI
Other Parts Discussed in Thread: TPS25820, TUSB564

Hello

 

For a new project we want to implement USB-C with Displayport ALT mode.

We have used the Toshiba TC358867XBG in another project, which makes 2-lane Main Link and AUX channel.

Currently this project uses 3 cables (Displayport, Power and USB2.0) but we want to have the advantage of USB-C and have USB, Power and Displayport over 1 cable.

So we want to connect this to the TUSB546 redriver and TPS25820 controller.

I think it should work but I am just a bit lost on how to connect everything.

 

The Toshiba chip has just 2 Lane Displayport and we are using USB 2.0(so these will go straight to the centre pins of the USB-C connector).

The TUSB546 has several options but which one should I configure?

We don’t have USB3.1 and only 2-Lane Displayport, but this option isn’t available.

Do I need to configure it as 4-Lane DP and don’t connect Dp3 and Dp4 on the TUSB546?

Or configure it as One Port USB3.1 + 2 Lane Dp and don’t connect the SSRx and SSTx.

And what do I need to do with the SSEQ pins when I don’t have USB3.1?

Can I configure them to the lowest gain?

 

I planned to use the TUSB546 in GPIO mode.

The TPS25820 will control the flipsel with the POL pin and the SINK pin will control the CTLSEL pins.

 

I have ordered the TUSB546 and TUSB564 kits so I can do some testing but it will take a while for them to arrive.

Would be great if you could help me a bit further.

And is it possible to have the schematics checked before I start working on the PCB?

  • +1
    TI__Guru**** 177476 points

    Hi,

    You can configure TUSB546 as a 4 lane DP re-driver, but leave USB SuperSpeed signal, DP2, 3, EQ, and SSEQ floating.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 10 points

    Hello

    Thanks for the quick reply.

    This is what I have so far.

    Current schematic

    The outputs of the TPS25820 are inverted by a dual inverter.

    So default the FLIP, CTL0 and CTL1 are all low and the TUSB546 is in power down.

    When a cable is connected the TPS25820 will pull it's SINK pin low, which causes the CTL1 to go high and enable the TUSB546 in 4-Lane DP mode.

    A Flipped cable will cause the POL pin of the TPS25820 to go low, which creates a high on the TUSB546 and selects the FLIP mode.

    The inverted SINK pin is also connected to the HPDIN on the TUSB546 and the Toshiba TC358867.

    I have selected the lowest gain option for the USB-up and USB-down gains, and put the DP gain in the middle as a starting point.

    Is this a good point of view or am I missing something?

  • 0 in reply to Mark Valentijn
    TI__Guru**** 177476 points

    Hi,

    I do not see an issue with this implementation. You may want to change the AC coupling capacitor from 100nF to 220nF for the DP lanes and TX1/TX2. You may also want to add optional 0.33uF capacitors on RX1 and RX2. I will also use 201 size capacitors.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 10 points

    Thanks.

    I will included your advice.

    I consider this issue solved.