This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMK00105: Drawbacks from above 2Vpp CLKin with Vdd 3.3V

Part Number: LMK00105

Hello E2E design support team,

The below is the waveform taken at the LMK00105 CLKin pin for existing product.

This shows that the CLKin level exceeds the specified range (0.3Vpp < Vi_se < 2Vpp).

Waveform indicates 2.0856V (ampl) and 2.2163V (pk-pk). 

The input signal is terminated with 75-ohm and AC coupled into CLKin.

The 75-ohm explains the high signal amplitude.

Moving forward, I can replace termination with 50 ohm (matching source, line and termination impedance).

Q1. What is the absolute maximum voltage for CLKin? Does it correspond to datasheet Vin specified at -0.3 to Vdd+0.3 V.

We supply Vdd with 3.3V.

Q2. Any reliability and performance concerns with the Vi_se amplitude exceeding 2V as shown above?

I can adjust for the new product, but want to determine if anything needs to be done for the existing product.

I understand the nature of my questions (i.e. out-of-range input operation), but would greatly appreciate your feedback on these.

Thanks for your support.

Regards,

JP

  • Hello JP,

    I am checking with our team and will get back to you with a response as soon as possible.

    Regards,

    Kia Rahbar

  • Hello JP,

    1. Yes, the absolute maximum voltage for CLKin corresponds to the Vin specified in the data sheet (-0.3 to VDD+0.3). 

    With that being said we strongly encourage operating within the VIH and VIL specs as shown below:

    The Vdd + 0.3 is just the Abs Max value, but you should not be continually operating that way.

    2.  The 2Vpp spec exists to prevent forward biasing a Base-Collector junction that should never be conducting in that direction. There are two areas of concern for exceeding this spec:  

    (A)  Crossing that base-collector junction threshold would temporarily turn on a parasitic pnp to substrate (p-) on each cycle, thus creating a momentary short to ground internally.  This path can be bad for long term reliability. 

    (B)  Prior to reaching that threshold, the amplifier input stage may enter saturation leading to degraded performance (reduced frequency capability, higher noise/jitter). 

    For these reasons, you must own the risk of using the device outside the Vpp spec on the datasheet.  Our recommendation is to work to improve the system setup to stay within the 2Vpp spec on the datasheet.

    Regards,

    Kia Rahbar