LMX2572: LMX2572 sysref_REFEAT mode output is abnormal when SYSREF is configured

Hello:
I have a question about LMX2572. LMX2572 is configured with sysref_REFEAT mode of SYSREF (signal frequency is 976.5625KHz), and an abnormally narrow pulse appears at the falling edge of output waveform, as shown below:

In sysref_REFEAT mode, when the signal is more than 1MHz, there is no problem mentioned above. However, when LMX2572 outputs sysref_REFEAT mode SYSREF as the SYSREF input of ADC12DJ5200, the abnormal waveform is measured, and the SYSREF waveform is measured as shown in the following figure (AC coupling is selected at this time, capacitance value is 100nf). The frequency of SYSREF is 1.953123MHz), the load is disconnected, and the waveform is normal after the ADC is disconnected

Is there a good solution to the above problems, or is there any design case for LMX2572 and ADC12DJ5200? Or similar design examples?

Cherry Zhou：

Hi,

Expert will working on this issue and please expect the response by next week.

Thanks.

,

Cherry Zhou：

Hi,

The SYSREF output on the LMX2572 also functions as an RF output.  As this output is AC coupled with a capacitor intended for high frequency, we wonder if it is related to the AC coupling capacitor size.

Thanks.