LMX2491: Output frequency abnormal and request a configuration

Vincent Li00

Intellectual 2035 points

Part Number: LMX2491
Other Parts Discussed in Thread: LMX2594

Hi Guys

Our customer is taking a LMX2594 board in debugging, encountered the following two problems:

1. My requirement is that RFoutA outputs 5GHz, RFoutB outputs SYSREF, and SYSREF requires Repeat mode. just like below:

Input Clock: 50MHz please see below schematic:

But when we finished the configuration, the output frequency is always incorrect: we need 5GHz, but the output always 4.047GHz; please see below the configuration:

2. SYSREF has no output:

We input 3.3V, 1MHz square wave at SYSRefReq pin; And we input 3.3V 1kHz square wave at SYNC pin.

Result: RFoutA and RFoutB ,there is no output for both. please see our configuration:

could you review my problem? and your feedback are very appreciated.

Thanks

-Pengfei

over 5 years ago

0 Dean Banerjee over 5 years ago

TI__Mastermind 28021 points

Pengfei,

For (1), the setup condition is not valid

a) Output B is selected for SysREF, yet SYSREF_EN is not enabled. SO this is not a valid condition.

b) I see the start VCO is "Invalid" and the start amplitude is 0. I think this is messing up the VCO calibration. Press the "Estimate Settings" and you should get some valid settings there

For (2)

a) same issue with Start Amplitude and Start VCO is likely the issue

b) for OUTB, also check on the User Controls tab to ensure that INPIN_IGNORE=0

TICSPro has some checks that are supposed to highlight some of the cells, but sometimes they do not work with different themes in windows 10.

Regards,

Dean