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Original question:

TUSB2E11: Power consumption during USB2.0 HS

TUSB2E11: Output differential vs. spec

Austin Allen
Intellectual 2555 points
Part Number: TUSB2E11

Hi team,

From the datasheet the eUSB output on the TUSB2E11 device is ~400mV differential.

 

Per the spec, the terminated is called out closer to ~200mV, and unterminated is ~400mV.

Why is the swing for the device set to 400mV rather than 200mV?

Thank you,

Austin Allen 

  • 0
    TI__Mastermind 27925 points

    Hi Austin,

    Thanks for pointing this out!  It could be a typo.  I will reach out to the author and let you know the explanation.

    Regards,

    Nicholaus

  • 0 in reply to Nicholaus_Malone
    TI__Mastermind 27925 points

    Hi Austin, 

    The way TX_DIF is measured is slightly different between the spec and the datasheet.

    From the datasheet you'll see that TX_DIF is measured with reference to Tx_CM, and is only a "peak" measurement from 0V.  The Tx differential measurement in the datasheet is "p2p" or peak-to-peak with reference to 0V.  This is why the measurement is doubled.

    Let me know if that makes sense.

    Regards,

    Nicholaus

  • 0 in reply to Nicholaus_Malone
    TI__Intellectual 2555 points

    Hi Nicholaus,

    Thanks for this. 

    As I read it, the common mode is set to 200mV for this interface (VE_TX_CM in your datasheet, matches VTX_CM in the eUSB spev).
    So even if Vpp is 400mV, this would imply:

    VTX_eD+ at 400mV,

    VTX_eD- at 0V,

    Differential swing is 400mV. ({200+200} –{200-200}) ?

    This would be different if the CM were 300mV for example, then Vpp diff of 400mV could imply:

    VTX_eD+ at 400mV

    VTX_eD- at 200mV ,

    Differential swing is 200mV.({100+300} – {300-100})

    Can you please confirm which it is ?

    Thank you,

    Austin Allen

  • 0 in reply to Austin Allen
    TI__Mastermind 27925 points

    Hi Austin,

    You can refer to the Figure 11-4 eye diagram in the datasheet to see that the differential is ~400mV.  The TX eye mask in the eUSB specification uses this type of measurement (eD+ - eD-), and it must be greater than 300mV.

    This is the idea behind the ~400mV TX_DIF in the spec.  The USB spec values in the datasheet are defined the same way at 800mV.

    I passed along the recommendation that the datasheet spec should be updated to avoid confusion in the future.

    Regards,

    Nicholaus