AD9172 TXEN issue


I was able to configure my AD9172-FMC-EBZ properly, and am able to generate a test sine wave output.  However, every once in a while after configuration completes, I see no output at all on both DAC channels.  I have the TXEN0 and TXEN1 pins connected to the FPGA via slow slew LVCMOS18 pins.  I have tried enabling TXEN via these pins after configuration as well as using the SPI register 0x0596 with value 0x0c to set TXEN via SPI (and ignore the TXEN0/1 pins).  For the SPI method, I first page the MAIN_DAC page using a write to register 0x0008 of 0xc0.  For both methods, I see that every once in a while the DAC outputs are absent after configuration.  If I run the configuration again, they come back.

I saw the PA protection feature in the datasheet, but from what I could tell, after reset, all of the turn off features are disabled.

Any idea what could be causing this behavior?