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HD3SS3212 AC Coupling for USB TYpe-C

Masaharu Katayama
Expert 1420 points
Other Parts Discussed in Thread: HD3SS3212

Hi

May I ask two questions?

Reference:

HD3SS3212 Datasheet, 8.3 Recommended Operating Conditions on page 4, and Figure 7 on page 12

USB3.1 Specification(rev1.0), Table 6-17 on page 6-30 and Table 6-18 on page 6-31

<Question1>

HD3SS3212 DS specifies Vcm 0V min to 2V max, and Vdiff 1.8Vppd max as Recommended Operating Conditions

USB specification (rev1.0) defines Vtx-diff-pp 1.2Vpp max, and Vtx-dc-cm 0 to 2.2V on the Tables 6-17 and 6-18.

And Vcm at the device will be 0V by using AC coupling (Figure 7 in the DS).  

Therefore I would like to confirm that HD3SS3212 will work at -06V to +6V swing (1.2Vppd) of USB3.1 specification.

<Question 2>

The figure 7 shows AC coupling capacitors between TYPE-C connector and HD2SS3212. On the other hand,  Figure 8 and 11 (and Layout example) shows the capacitors between Host/Device and HD3SS3212. Isn't it necessary to put the coupling capacitors between the connector and HD3SS3212 because Vtx-dc-cm max is 2.2V but HDS3SS3212 Vcm max is 2V at recommendation (even absolute max is 2.5V)?

Best regards,

Masa

  • 0
    TI__Mastermind 36085 points
    Hello,

    The answer for the question 1 would be yes, however I have to review one detail with design, please wait for my response.

    regarding the AC caps, the answer is that the customer only needs the AC coupling caps in one side of the TX lanes on the multiplexer, and the customer is free to have the AC caps placement as he needs.

    Regards,
    Diego.
  • 0 in reply to Diego Cortes
    Expert 1420 points

    Hi Diego,

    Thank you for your quick response.

    I have one typo correction in my <question 1> and would like to add <question 3> and <question 4>.

    Correction in <Question 1>

    I would like to confirm that HD3SS3212 will work at -0.6V to +0.6V swing (1.2Vppd) of USB3.1 specification.

    <Question 3>

    Absolute Maximum Rating in HD3SS3212 DS specifies MIN -0.5V of Voltage of Differential I/O 

    However Differential Input will swing to negative -0.6V for example, even -0.9V at max Vdiff 1.8Vppd case. The -0.5V is not enough and support to swing upto -0.5V meaning 1Vppd? 

    (Differential signal over Type-C connector is transmitted after AC coupled (Vcm=0) in USB3.1 Specification.)

    <Question 4>

    Recommended Operating Conditions specifies
    max Vcm=2V and max Vpp=1.8Vpp

    it means max signal will be 2.9V (2V+0.9V). Is it okay even Differential I/O Voltage MAX in Absolute Maximum Rating is 2.5V?

    Best regards,

    Masa

     

     

  • 0 in reply to Masaharu Katayama
    Expert 1420 points

    Hi Diego again,

    I just draw what I understand Vdiff and Vcm from USB3.1 Spec. I am not sure if this is correct. 

    Regarding to <question 3> and <question 4>, are MIN/MAX Vdiff -0.6V/2.8V?

    Best regards,

    Masa

  • 0 in reply to Masaharu Katayama
    TI__Mastermind 36085 points
    Hello Masa,

    The 1.8Vpp is differential peak-to peak spec. Each signal will have 0.9V swing with 0.45 up and 0.45 down from VCM. As you can see, this value is indeed greater than the USB spec you mentioned (for VCM=0).

    Best regards,
    Diego.
  • 0 in reply to Diego Cortes
    Expert 1420 points

    Hello Diego,

     

    Thank you for your esponse. However my question is based on 8.1 Absolute Maximum Rating in the HD3SS3212 Datasheet.

    It specifies -0.5V min to 2.5V max. However USB3.1 Spec looks -0.6V(VCM=0) min to 2.8V(VCM=2.2) max.

     

     Best regards,

    Masa

  • 0 in reply to Masaharu Katayama
    TI__Mastermind 36085 points

    Hi masa,

        I do believe that the usb spec establishes 1.2Vpp, therefore each signal will have 0.6V swing with 0.3 up and 0.3 down from VCM=0. Therefore should not be an issue with absolute maximum ratings of our device and the USB spec. Please let me know if the spec is defined as Vpp.

    Regards,

    Diego.

  • 0 in reply to Diego Cortes
    Expert 1420 points
    Hi Diego,Thank you very much for your answer again. I understand Vppd and Vpp.
    Best regards,Masa