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level shift and fan out of 1.2V clock

Galen Wong
Prodigy 10 points
Other Parts Discussed in Thread: LMK00105

Hello

I need to take a 3.3V (single ended)low noise, 60MHz,clock and fan it out to 4 separate, 1.2V,converters(single ended).  The skew between each of the four clocks is very sensitive.  I would like to keep it below +/- 50 ps budget for this part.  Are there any parts that will work down to 1.2V output level.  T

Thanks

Galen

  • 0
    TI__Mastermind 32575 points

    HI Galen,

    You can use the LMK00105 5-output LVCMOS clock buffer/level translator which supports 3.3 V core voltage (Vdd) for the input clock buffer and independent output supply (Vddo) which supports 1.5 V to 3.3 V for the LVCMOS output buffers. 

    There are typical plots in the datasheet that show the LVCMOS Output Swing vs. Frequency with 50 ohm load.  It appears the LVCMOS output swing does not reach rail-to-rail due to the 50 ohm load and limited output driver current of ~27 mA (=1.35 V / 50 ohms, at Vddo=2.5 V and f_out <= 200 MHz).  Note that the device's LVCMOS output resistance is 50 ohms typical.

    If you have a lighter load (high impedance input) such that the output swing isn't limited by the drive current, you may use a voltage divider with small resistor values to achieve the desired 1.2 V level...just be aware of the parasitics that could cause attenuation of high-frequency components of your clock signal.

    Regards,
    Alan