AnsweredAssumed Answered

AD9912 clock problem

Question asked by arunkuttath on Jul 9, 2017
Latest reply on Jul 9, 2017 by mcee

Hi JLKeip, Kevin.G, DSB, LouijieC

We are using the AD9912 based PCB in our project.

1) The initial SPI communication was up. But the device part ID read as 0x1982 instead of 0x1902 in the datasheet. Is that a problem?


2) We have given the Reference clock a crystal (P/N: 8Z-25.000MEEQ-T) of 25MHz. We are not getting any frequency output and BUFFERED registers are not updated successfully, but we can read back the MIRRORED registers successfully, that we have written to.  While probing the crystal we got a dc value of 1.2V. What is the reason behind that? (We have already changed three number of crystals with as assumption that the crystal might be damaged.)


3) With an assumption that the crystal in ADD9912 as reference clock no longer works, we have given an external clock (CMOS output of 1.8V) to the reference clock through wires. 

Even though the SPI is up, it cant read back the FTW that we have written in. 

We did all I/O_UPDATE internally(writing 1 to the register 0x0005) and externally (pin Low to High).

The automatically clearing update bit is not autoclearing and remains in logic 1.

But we are getting 0x27D000000000 value from the FTW and getting a frequency around 15.5MHz everytime irrespective of the update.

Semeone please help what might be the issue at the instances of crystal connected  and CMOS clock connected as reference.

(please take the query as reference :AD9912 heating up issue, and the communication failure as well. )