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Driving LMK04816 Input with DC-coupled CML source

Niels Koll
Expert 1950 points
Other Parts Discussed in Thread: LMK04816

Hello,

I need to drive CLKin0 of the LMK04816 with an output that uses CML (SY58040U).

As the input clock may be very slow (down to 1kHz), I think I need a DC-coupled connection from the SY58040U-output to the LMK04816-Input.

0066.sy58040u.pdf

Will this work?
What is the recommended termination needed?


Regards,
Niels

  • 0
    TI__Mastermind 24205 points

    HI Niels,

    This should work. Add a 100 ohms differential resistor across the SY58040U output pair close to the LMK04816 CLKin Inputs followed by two 0.1uF AC coupling capacitors. The AC coupling capacitor together with the input impedance of the CLKin inputs should not filter the 1 kHz. The minimum input frequency on CLKin for LMK04816 is 1 kHz. The minimum required slew rate is 0.5 V/ns (which would be met given the CML outputs from SY58040U have a fast/rise fall time of 60ps).

    While selecting the VCXO, ensure that its input impedance is > 500K since PLL1 is operating at a low PFD rate. This would limit any charge pump leakage.

    Regards

    Arvind Sridhar

  • 0 in reply to Arvind Sridhar
    Expert 1950 points

    Arvind,

    thank you.

    Have a nice weekend,
    Niels