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Can't seem to get the AD9959 to accept the REF_CLK inputs

Question asked by on Apr 29, 2018
Latest reply on May 7, 2018 by

I have an AD9959 device whose clocks (Ref-Clk/Ref_Clk*) are being driven with a LVPECL 25Mhz driver and capacitively coupled into the chip pins (0.1uF).  I have never gotten it to do anything.   CLK_MODE is grounded.  After power-on or Master_Reset, there is no Sync_Sclk present and chip doesn't seem to work with any configuration I set via SPI.  The clock signals are clean and with both inputs at 0.8V p-p with a differential voltage of 1.6v at the chip.  The inputs are capacitor coupled into the chip.  Average voltage at the chip is about 1.4V..  Supplies are 3..3V (DVDD_IO) and the others 1.8V.  PWR_Down is ground, master_reset is low.  Kind of out of options.  Does anyone have any ideas on how to get the clock working?