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AD9542 REFBB Offset Limit Question

Category: Hardware
Product Number: AD9542, AD9545


I have an external 10,000 Hz reference signal connected to REFBB on an AD9542 but I'm having trouble getting it non-fault lock.

The reference signal has a nominal tolerance of 600 ppm which I interpret as the signal can be anywhere from 9,994 to 10,006 Hz.

According to my calculations, I think this yields a delta p of 599640 ppb [from the formula -600E-6/(1+600E-6)*1E9= -599640.2159]

This is what is programmed into the ΔTOL register for REFBB [0x092658].


In my current rig, the actual reference input is measured at 10,003 Hz (and it's not easy for me to change this) and I can not get a valid reference lock: REFBB status (0x3008) only ever reports 'fast' and 'fault'. The register is working as it reports 'los' (and sometimes both fast and slow) when the signal is removed.

I believe that the 52 MHz chip reference oscillator is good as I am able to synthesize a 10,000.00 Hz signal on the outputs.

Any suggestions greatly appreciated.