We are designing in a LTC6951 to provide clocks for ADC and FPGA.
Independent of clock settings (either those from data sheet examples with external clock as well as with own settings) we always get the following error image:
VCO obviously is somewhere around 4.22 GHz
Lock detect error is detected: Register 00 is h49.
Register 02 is h01, i.e. LSB remains "1" (CAL = 1) whenever Calibration oder autocalibration shall be executed. Our application operates with reference clock 38,4 MHz, Loop filter variant 2 (from LTC6951 wizard) with c2 = 1 nF, R1 and RZ 100 Ohm, Ci 68 nF, Cp 1.5 nF.
Register programming is as follows:
Reg-No / Reg Value:
h03 h78 (also tested with 70)
We do NOT use multiple byte transfer on SPI, but single byte transfer. Each register setting has been checked using read commands.
We tested this on two boards to exclude the possibility of singe part failure.