AnsweredAssumed Answered

AD9747 doesn't work

Question asked by Mike_sd4y on Feb 28, 2015
Latest reply on Mar 6, 2015 by larrywelchusa



I'm working on the bring up of a new custom PCB including the AD9747.

In one of the very first trials, I could get it to run a simple ramp on its output, but with no other design in my FPGA it will provide any output.

I've already tried writing all registers, writing only several, writing no registers - only toggling the reset pin after power up.

I've no idea why it won't output any data - sample rate is already reduced to 122Msps - s/h times for data and clock are well inside the limits.

The clock input is AC-coupled LVDS with 400mV VCM. The differential voltage swing on the input is ~600mV.

Sample clock is applied once configuration on SPI is finished. The differential output is connected to a simple resistor network and a differential probe.

I've checked already:

- supply pins

- FSADJ - 1.2V - 100pF in parallel tested as noted in another thread here

- REFIO - 1.2V

- DCO - 122MHz - ok

- data/clock timing

- SPI interface timing / data content


Attached some screenshots I've made during the tests.


If anybody has an idea of what could be wrong, please let me know.


Thanks, best regards