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LMX2592: VOSCin Abs Max

Part Number: LMX2592

Hi,

The datasheet Abs Max states VOSCin can handle up to 1Vpp with Vcc = 0V.  Is this the case for each pin 8 and pin 9, separately (S/E) or together (differential)?  For example, if VOSCin is driven S/E, does this mean that OSCinP (pin 8) can handle up to 1Vpp (4 dBm)?

In case the 1Vpp limit is for the case in which VOSCin is driven differentially, what is the Abs Max for the S/E case?

Thanks,

Marjorie

  • Hi Marjorie.

    I'm not sure of the answer right now. I'm asking the design team for more details on this spec and will get back to you soon.

    Regards,
    Hao
  • The 1Vpp is for both differential and single ended.

    When using differential, the differential swing is 1Vpp max; when using single-ended, the single ended swing is 1Vpp max. 1Vpp is specified for OSCin_P - OSCin_N.

    Regards,
    Hao
  • Hi Hao,

    Thank you for following up and responding to my question.  The details of the answer are somewhat unexpected.  I would have expected that the voltage swing per pin while unpowered would be limited by the ESD diodes, and therefore be different for the S/E vs differential case.

    Kind regards,

    Marjorie

  • Majorie,

    In this datasheet, I think that the differential voltage would be VoscinP- VoscinM or the difference of the voltage between the two pins. IN the single-ended case, teh assumption is that the complimentary input pin is grounded through an AC capacitor (and 50 ohm shunt) to ground.

    But that being said, I notice that the electrical specifications say a max voltage of 2Vpp, yet the abs max rating is 1.8V, so I don't have very high confidence in this datasheet. I need to look into this.

    Regards,
    Dean
  • Thanks, Dean!

    I will very much appreciate having a high level of confidence for my design.  It is very important to make sure that the LMX2592 input is not over-stressed for the full variety of operating conditions.

    Kind regards,

    Marjorie

  • Marjorie,

    OK, I have confirmation, here's how it works:

    1. If Vcc=0, then you can put 1Vpp per pin. This means that if this is single-ended, it is 1Vpp, but if it is differential, it is 2Vpp.
    2. Iv Vcc=3.3, then you can put 1.8Vpp per pin. This adds up to 3.6 V differential. So the 2Vpp differential spec is OK.

    This assumes the signal is AC coupled.

    Regards,
    Dean
  • Hi Dean,

    My input is AC-coupled, so your response applies 100%.  Thanks so much for the clarification!

    Kind regards,

    Marjorie