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AD9864 LC Tank Will Not Calibrate.

Question asked by RHorton on Feb 7, 2017
Latest reply on Feb 14, 2017 by PMH

I am developing an application with the AD9864.  The majority of the example designs in the datasheet are exactly what I need (e.x. Fclk=18MHz,  +/-5Khz Decimation filter BW, 20Ksps, etc.), so I have followed the reference designs in the datasheet exactly.  All seems to be working more or less (the 18MHz VCO is fairly weak [~ 1Vpp, 1.6V DC offset] measured at pin 43 [LOP]), but I cannot not get the LC & RC Resonator Calibration to work.  I am following the script on page 46 of the datasheet exactly, however, when I send 0x03 to register 0x1C, most of the time it will lock up the SPI bus and force me to do a POR.  When it doesn't lock up the SPI, the value of 0x1C never clears.  The values of registers 0x1D, 0x1E remain 0x00.  Note that the values in the LC tank are exactly as recommended in the datasheet (50 Ohm, 2x 10uH, and 180pF).  Any help would be GREATLY appreciated.  We have been stuck on this issue for weeks now.  Note, R509 in the attached has been changed to 1.96K.

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