DAC38RF80: Is there any way to tell if the DAC has seen the required number of SYSREF edges in initialization

Matt Wilbur

Part Number: DAC38RF80

Hello again,

The motivation for my question regarding the SYSREF capture circuit (which I still need to follow up on) is because we were having a failure in our system where we were not seeing RF output, and it seems like I was able to fix the behavior by adding a delay before turning off the SYSREF (the whole initialization sequence was given to me by an FPGA designer who doesn't work at my company anymore).

So, the heart of my question is this: Is there anything I can do to ensure the various required 2 rising SYSREF edges are seen, as outlined in Figure 167 of the DAC38RF8x datasheet (text in red in the block AFTER that labeled "Start SYSREF Generation"), in the 4 separate steps listed there? Is there a condition that can be checked by reading particular registers, for example?

Thanks again,

Matt

over 4 years ago

0 jim s over 4 years ago

TI__Guru* 91947 points

SYSREF_NCO.pptx 2553.SYSREF_register_test.docxMatt,

See if these two documents help. This will require using the NCO of the device to verify SYSREF is received properly.

Regards,

Jim

0 Matt Wilbur over 4 years ago in reply to jim s

Prodigy 40 points

Thanks, Jim. I'll try to look at that - a bit tough with my current restricted access to the office and lab.

At run time (in the field as it were), is there any way to see that the SYSREF has been enabled for sufficient time so as to know if the requirements listed in Figure 167 that I originally mentioned are met?

Matt

0 jim s over 4 years ago in reply to Matt Wilbur

TI__Guru* 91947 points

Matt,

Other than what I sent, I do not know of any other means of knowing that Figure 167 is met. Does your system have SYSREF AC or DC coupled? If DC coupled, is the common mode voltage at the correct level? Is the amplitude correct in either case? I have attached another document that may be of help. This document is targeting another DAC family but much of the info applies to this part as well.

Regards,

Jim

DAC38J84 SYSREF Configuration.docx

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DAC38RF80: Is there any way to tell if the DAC has seen the required number of SYSREF edges in initialization