LMX2592: LMX2592 OSC input SPEC

Feng bin Su

Part Number: LMX2592

Hi team,

My customer is evaluating our LMX2592 for their design and not sure whether the input waveform as below meets our LMX2592's spec.

Please refer the input clock as below figure.

over 3 years ago

0 Noel Fung over 3 years ago

TI__Guru** 108130 points

Hi Feng,

Your clock has a voltage swing close to 3V, is it a CMOS clock?

The max. input voltage swing for the LMX2592 is 2V, you need to reduce the voltage swing. Below is one of the possible configurations for a CMOS reference clock. The 50Ω resistor will reduce the voltage swing to below 2V.

0 Feng bin Su over 3 years ago in reply to Noel Fung

TI__Expert 8760 points

Hi Noel,

Thank for your help.

Is there a requirement for slew rate of CLK? The following is an updated waveform LVDS 1.8V, can you help to confirm if this waveform is OK?

0 Noel Fung over 3 years ago in reply to Feng bin Su

TI__Guru** 108130 points

Hi Feng,

The slew rate of a 122.88MHz LVDS signal is going to be good, the poor slew rate of your plot is probably due to not enough bandwidth of the scope or the probe. Looks like the bandwidth of the scope is limited to 350MHz which is not enough for a 122.88MHz square wave signal.

The schematic is good. A simpler termination architecture is use a 100Ω resistor across the _P and _N traces instead of using two 50Ω shunt resistors.

0 Feng bin Su over 3 years ago in reply to Noel Fung

TI__Expert 8760 points

Hi Noel,

update the waveform as below. Let me know if there is any concern about the input clock from LMX2592. Thank!

0 Noel Fung over 3 years ago in reply to Feng bin Su

TI__Guru** 108130 points

Hi Feng,

this signal looks good to me.

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LMX2592: LMX2592 OSC input SPEC