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CDCLVP111-SP: +2.5V LVCMOS Input

Luis Landy
Prodigy 100 points
Part Number: CDCLVP111-SP
Other Parts Discussed in Thread: CDCLVP111,

Following the datasheet of CDCLVP111, when utilizing an LVCMOS Oscillator we Bias the second input of CDCLVP111 to half the voltage of the Oscillator going into the primary input. Considering our Oscillator is powered at +2.5V and the biased voltage is +1.25V this would mean the input amplitude parameter for the datasheet below would be +1.25V correct?

If this is so then would it be correct in saying that this gives us a margin of 50mV from the max input amplitude?

  • 0
    TI__Genius 12835 points

    Hi Luis,

    What are your VIH/VIL values?

    Regards,

    Jennifer

  • 0 in reply to Jennifer Bernal
    Prodigy 100 points

    Hi Jennifer,

    Typically VIH = 2.5V and VIL = 0V. The only other parameters shown in the datasheet is VIHmin = 2.25V (0.9xVDD) and VILmax = 0.25V (0.1xVDD).

  • 0 in reply to Luis Landy
    TI__Genius 12835 points

    Hi Luis,

    Then VID (input amplitude) would be VIH - VIL = 2.5V. That is over datasheet limit. These parameters should be of a single ended measurement (CLKIN_P OR CLKIN_N).

    Regards,

    Jennifer

  • 0 in reply to Jennifer Bernal
    Prodigy 100 points

    Hi Jennifer,

    I did follow this configuration as per the datasheet of CDCLVP111-SP:

    Not sure if this may clear things up for the parameter limit. We placed the secondary input Vth = 1.25V, would this still be over the limit?

  • 0 in reply to Luis Landy
    TI__Genius 12835 points

    Hi Luis,

    See above for my crossed out edit. VID is used for differential signals in this datasheet. When working with LVCMOS (single ended) signals, you may disregard the VID spec. Using 2.5V OSC with Vth = 1.25V is acceptable as shown in the datasheet.

    Regards,

    Jennifer

  • 0 in reply to Jennifer Bernal
    Prodigy 100 points

    Hi Jennifer,

    Is there any type of parameter on the datasheet we can refer too? The only concern is any type of overshoot/undershoot that may occur with a variance in temperature, we want to analyze and confirm that it would not present an issue for the CDCLVP111-SP.

  • 0 in reply to Luis Landy
    TI__Genius 12835 points

    Hi Luis,

    These parameters need to be met: VIH, VIL, VCM, VTH. VTH is defined by the equation you used above. Adding a series resistor may help reduce overshoot/undershoot. You can also see how the device will react with the IBIS model.

  • 0 in reply to Jennifer Bernal
    Prodigy 100 points

    Hi Jennifer,

    I am not connecting the dots here to be honest with VIH and VIL. VCM = VTH correct? And for the LVCMOS Oscillator input is there a parameter that shows me how much overshoot or undershoot is allowed? Also just to be certain, with an LVCMOS input we can completely disregard the VID parameter correct?

  • 0 in reply to Luis Landy
    TI__Genius 12835 points

    Hi Luis,

    The incorrect image was pasted (I was mistaken with another part).

    Since the LVCMOS characteristics are not listed in the datasheet, I recommend using VIH = VCC and VIL = 0, VCM = VTH, VTH = (VIH-VIL)/2 as your parameters. In your case:

    VIH = 2.5V

    VIL = 0V

    VCM = 1.25V

    VTH = 1.25V 

    For the overshoot/undershoot, I suggest using using the VCC recommended limits are reference but also confirming with the IBIS model.

    The LVPECL DC Electrical Characteristics table focuses on the LVPECL voltage swing (VID) which is why it is restricted to 1.3V. With LVCMOS, VID = 2.5V is okay. If you are concerned about the overshoot/undershoot, you may attenuate the input with a resistor divider circuit.

    Regards,

    Jennifer