I am trying to build a local oscillator synthesizer around an ADF4002.
For testing purposes I am driving the serial interface from a Bus Pirate. I seem to be able to send commands to the latches successfully. I can program MUXOUT to DGND, DVDD or SDOUT. when programmed to SDOUT the output matches the input, advanced by 1 clock period.
The CP output remains high impedance. When I program MUXOUT to the N or R divider output the result is a logic low with no hint of anything counting. I am stumped at the moment. I am thinking that I may not be understanding the correct protocol. The datasheet makes mention of an 'internal reset pulse'; I am wondering if that is what is stopping the counters. I believe the commands I am sending are as follows:
AVDD and DVDD are 3V, charge pump is 5V. My FRF is 4.915 MHz and FREF is 38.88 MHz. FRF is AC coupled; FREF is DC driven from 3V CMOS 74AC1G04 inverter.
Any suggestions as to what might be wrong would be greatly appreciated. Thanks.