DAC38J84 Sysref setup/hold alarm

Hi Marc-Antoine,

The "SYSREF setup/hold" alarm is not quite what you'd expect. It is meant to measure a signal of DACCLK / 8 at the SYSREF pins and looks for four successive 1's and four successive 0's after capturing the signal with the DACCLK. This is not a realistic SYSREF signal, so it is not really a "SYSREF setup/hold" alarm - you would have to run the DACCLK/8 pattern first, then switch the frequency to the SYSREF frequency. Further, there is a clock frequency limitation on this alarm that makes it unusable for most cases - thus why it was "mostly" removed from the datasheet.

There is the SYSREF error alarm though - although I'm not sure it can be used to detect setup and hold times. Let me talk to design to see if there is a way to make it work for this.

Regards,
Matt Guibord

Hi Matt,

Thank you for this update.
Sending a DACCLK/8 pattern will not be something easy in my case but it still give me a way to adjust SYSREF signal.
What is the clock frequency limitation you are talking about?
I'm currently using DACCLK at 2000Mhz, but I plan to use a DACCLK up to at 2500Mhz.

Do you have anything new about SYSREF error alarm?

Regards,

Marc-Antoine

Hi Marc-Antoine,

The clock limitation is 500 MHz, so not usable.

I have not had success with the SYSREF error alarm. I don't think it can be used for setup/hold time testing. I am trying to experiment with using the NCOs and monitoring the output while constantly syncing. If the setup and hold times are violated then the output should be messed up. I'll report back.

Regards,
Matt Guibord

Thanks for the update, I'll stay tuned

Florian,

See if this document helps.

Regards,

Jim

8880.DAC3xJ8x Device Initialization and SYSREF Configuration.pdf