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TUSB1210: about of reference clock of TUSB1210

chunli Liang
Intellectual 310 points

Part Number: TUSB1210

Dear TI Supporters,
 
I am currently working on a design using the USB TUSB1210BRHBR. While reviewing the datasheet, I noticed that the REFCLK pin (Pin 1) does not have detailed VOH/VOL DC characteristics. The datasheet states the following:
 
"Connect to square-wave reference clock of amplitude in the range of 3 V to 3.6 V when Pin 26 (CLOCK) is required to be Output mode."
 
I am unclear about the meaning of "the range of 3 V to 3.6 V." Specifically, I plan to drive the REFCLK pin using a 3.3V crystal oscillator, but its output does not seem to meet the 3.0V to 3.6V amplitude requirement. For example, the VOH of DSO211SXFAB-26.0000MHZ oscillator has an output of VCC × 0.9 = 3.3V × 0.9 = 2.97V, which is below the 3.0V lower limit.
 
Could you please answer the following:
 
Is the 3.0V to 3.6V amplitude requirement strict?
 
Any guidance or additional specifications would be greatly appreciated. 
 
Best regards,
Chunli Liang.
  • 0
    TI__Guru**** 161886 points

    Hi Chunli:

        REFCLK  amplitude  is at least 3V square wave. What  is typical  amplitude   in  DSO211SXFAB  oscillator  datasheet?

    Best

    brian

  • 0 in reply to Brian Zhou
    Intellectual 310 points
    Hi Brian,
    Thank you for your reply that the REFCLK input requires a square wave with an amplitude of at least 3V.
    We have reviewed the datasheet for DSO211SXFAB.
    Supply voltage is +3.0V to +3.6V.In my design the VCC is 3.3V(type).
    1 level output voltage (VOH)= VCC × 0.9 = 3.3V (TYP) × 0.9 = 2.97V.
    However, we checked the oscillator used on the TUSB1210BRHBR evaluation board (TUSB1210EVM):
    ECS-1633-260-BN is used In the TUSB1210EVM.
    VDD:+3.135V to +3.485V. In the TUSB1210EVM,the VCC is also 3.3V(type).
    1 level VOH = VDD × 0.9 = 3.3V (TYP) × 0.9 = 2.97V,too.
    Since the typical VOH (2.97V) of the oscillator of  the TUSB1210BRHBR evaluation board is below the stated 3V minimum amplitude, I have two questions:
    1.could you tell me why the TUSB1210EVM use the ECS-1633-260-BN?
    2.could you tell me the current consumption of the REFCLK pin. 
      I did not find the current consumption of the REFCLK pin in the datasheet. 
      I think the output voltage of oscillator is concerned with the current consumption of the REFCLK pin.
    Thank you for your support. Looking forward to your reply.
    Best regards,
    Chunli Liang.
  • 0 in reply to chunli Liang
    TI__Guru**** 161886 points

    Hi Chunli:

        Voh isn't the same as total output voltage, it defines the minimum voltage level that represents a logic '1' . the real output voltage should be >3.1V with 3.3v supply .

    Best

    Brian

  • 0 in reply to Brian Zhou
    Intellectual 310 points
    Hi Brian,
    Thank you for the previous explanation. I understand the distinction between VOH and actual the real output voltage.
    However, to ensure robust design, I must plan for worst-case, not just typical. Relying solely on typical performance for a clock signal introduces unacceptable risk to design.
    To finalize the clock driver circuit design for the REFCLK pin, I need to ensure it has sufficient drive capability under all conditions.
    Could you please provide the current consumption of the REFCLK pin?
    I think the output voltage of oscillator is concerned with the current consumption of the REFCLK pin.
    Thank you for your support. Looking forward to your reply.
    Best regards,
    Chunli Liang.
  • 0 in reply to chunli Liang
    TI__Guru**** 161886 points

    Hi  Chunli:

          Max current for REFCLK is  around 3ua, it will not affect  oscillator output voltage much.

    Best

    Brian