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LMK1C1102: Jitter spec at 3.3V input

Julian Dietrich
Prodigy 30 points
Part Number: LMK1C1102

Tool/software:

Hello Forum,

in the datasheet it is stated:

Supply voltage: 3.3 V, 2.5 V, or 1.8 V – 3.3-V tolerant input at all supply voltages

I want to use 1.8V supply, but 3.3V input clocks.

What happens with the jitter specification at this scenario? I haven't found something in the datasheet.

Can I still rely on the Jitter specs for VCC_1.8V or will that change with 3.3V inputs?

Thanks in advance!

BR Julian

  • +1
    TI__Genius 10975 points

    Julian,

    There should be no problems and you should see the same expectations on the jitter.

    Quick questions, is the input signal a since wave? If so, two important things to note: 1) the LMK1C needs to be biased externally to VDD/2 (this is true regardless what type of input is fed into the LMK1C) and 2) when biasing the LMK1C externally with a VDD = 1.8V, the resulting DC bias will be VDD/2 = 0.9V and with a 3.3V signal, the inputs tot the LMK1C will oscillate from -0.75V to 2.4V. The bottom level violates the absolute max spec of the LMK1C. To solve this you can either connect the bias of the LMK1C input to a 3.3V rail somewhere in your board or you can add a 50Ω to GND to half your swing to the LMK1C and not violate the abs max spec.

    Best.

    Andrea

  • 0 in reply to Andrea Vallenilla
    Prodigy 30 points

    Thx Andrea!

    And, nope, not a sin wave, it's a 25MHz clock coming from an MEMS.