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TUSB211 - EQ setting and C4 capacitance

Hirotaka Matsumoto
Guru 27585 points
Other Parts Discussed in Thread: TUSB211

Hi all

Would you mind if we ask TUSB211?

<Question1>
Our customer would like to use USB2.0 with using 10m cable.
So, we heard from you that it is required two TUSB211 as the redriver.
In this case, how much of EQ gain settinng should we choice(from Level0 to Level3)?
Of course, we recognize that it depends on the cable length.
If you have some experience about it, could you let us know?

<Question2>
On the datasheet P8, why does C4 require?- Only for the delay, for noise?

<Question3>
The max cable length of USB2.0 is 5m.
So, if the cable length is less than 5.0m, it is not required to add TUSB211 for redriver, is it?

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Mastermind 36085 points

    Hello, 

        I would start by using level 1, but as you mentioned, it depends on the cable length and quality. The capacitor is required and used for both purposes; delay and reduce noise. At last, you are right, if the USB cable is shorter shorter than 5m, then the TUSB211 is not necessary.

    Regards,

    Diego. 

  • 0 in reply to Diego Cortes
    Guru 27585 points

    Diego san

    Thank you for your reply!

    When we acheive 10m(less than 10m) cable length, we heard the method on the E2E as following; 
    HOST - TUSB211 <----10M_cable---->  TUSB211 -  Slave
    Of course, we consider this way.

    Then, is it possible to archeive the method as the following?
    HOST <----10M_cable----> TUSB211 - Slave

    And then, if it is possible to compensate the DC drop of VBUS(you mentiond other post), is it possible to over 10m cable length? 
    https://e2e.ti.com/support/interface/usb/f/1008/p/462775/1663107#1663107

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Mastermind 36085 points

    Hello Hirotaka -san,

    I recommend to place the TUSB211 in the middle of the cable, and regarding the VBUS drop, it is also possible to provide a higher VBUS at the beginning of the cable to compensate the cable loss.

    Regards,

    Diego.

  • 0 in reply to Diego Cortes
    Guru 27585 points

    Diego san

    Thank you for your reply and your cooperation!

    We would like to confirm one point.
    The content you mentioned is as the following, isn't it?

    <Schematic>
    HOST <----5M_cable---->  TUSB211 <----5M_cable---->  Slave

    If we use conpensation of VBUS, is the following correct?
    HOST(VBus conpensation) <----5M_cable---->  TUSB211 <----5M_cable---->  Slave

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Mastermind 36085 points

    Hirotaka -san,

        Yes it is, based on that the standard USB2 supports up to 5m and the re-driver will receive valid  HS signaling.

    Regards,

    Diego.

  • 0 in reply to Diego Cortes
    Guru 27585 points

    Diego san

    Thank you for your reply and your cooperation always.

    At last, we would like to confirm one point.

    If we construct as the following,  Slave side can get much EQ effect.
    However Host side can't get much EQ effect. That's why, you metioned you recommend to place the TUSB211 in the middle of the cable.
    Is our recognition correct?
    (TUSB211 is able to use bidirectional way.)

    Host <----10M_cable---->  TUSB211 -  Slave

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Mastermind 36085 points

    Hirotaka-san,

        If you have the 10m cable before the TUSB211, then the re-driver might not be able to recover the input signal to the device, meanwhile the recovered signal from the device to the host might not be able to reach the Host with enough signal quality to be detected. That's why, remember that the TUSB211 is a bi-directional device and that the 10m is quite a long distance.

        A second option is to have two re-drivers, one on each side of the cable.

        So I highly recommend you to use two EVMs in order to test both configurations using different EQ settings and determine which solution is better for the customer.

    Regards,

    Diego.

  • 0 in reply to Diego Cortes
    Guru 27585 points

    Diego san,

    Thank you for your so kind reply and your cooperation!
    We got it!

    We appreciate for your help always.

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Diego Cortes
    Mastermind 8610 points
    Hi Diego,

    I'd like to ask the configuration below.

    HOST <----cable----> TUSB211 <----cable----> Device

    Can TUSB211 equalize the bi-directional signal (from HOST to Slave or from Device to HOST) automatically?
    Is it general way?

    General full duplex application like serdes(USB2.0 is hall-duplex), equalizer devices are placed near both RX side(master and slave) to equalize the decay signal via cable.
    Re-driver devices with De-emphasis are placed near both TX side(master and slave).
    So I don't understand that TUSB211 which has EQ function is only one in the middle.

    Regards,
    ttd
  • 0 in reply to ttd
    TI__Mastermind 36085 points
    Hirotaka-san,

    The TUSB211 is capable of qualize the bi-directional signal, this device improves the slew-rate by injecting current to the signal; this leads to a loss reduction caused by the RC parasitics on the channel.

    Regards,
    Diego.
  • 0 in reply to Diego Cortes
    Mastermind 8610 points

    Hi Diego,
     
    Thank you for your reply.
    I'm not Hirotaka-san. I check your discussion on E2E.
    I would like to check the reason why only one TUSB211 is placed in the middle of cable.
    But you said that it is ok.

    In my case, cable length is under 5m, so I'd like to use this way.

    Best Regards,
    ttd