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ADF4350 timing problems

Question asked by andyrobertson on Oct 20, 2011
Latest reply on Oct 25, 2011 by rbrennan

Attention:   Austin Harney

 

We are plagued by not being able to reliably program only one of 3 identical synthesizers.  At one point or another, I have verified all setup and hold parameters in the datasheet t1 thru t7 and we seem to have greater than 2X margin on every spec.  We program all 6 words in the following order: W5, W4, W3, W2, W1, W0.  Not much evidence of any kind of glitching or even ringing, but I do not have a FET probe or anything faster than 100MHz probe on a 500MS/s DSO.  Oddly, problematic synth. is closest to FPGA.  Layout and signals look clean, & textbook.  FPGA designer suggested 237-ohm resistor and 100pF capacitor in series-shunt with SCLK pin & claimed chip "seemed happier"  Currently, all 3 SPI lines are 237 in series shunt with 22pF, and I don't see anything bad.  I personally don't think there are any glitches.  I suspect t6 may need to be at least one serial clock time.  Currently it is ~24ns.  Perhaps there are other timing issues?

 

Preliminary datasheet had some reserved bits in W5 that were all zero; now in Rev A, some are 1.  Does it matter?

 

Digital Lock Detect Bits (in W5) see figure 29.  00-Low, 01-Digital Lock Detect, 10-Low, 11-High.  Datasheet very vague.  Can you provide more detail?  We want the digital lock detect to go High when locked.

 

Word 5 isn't displayable using ADI eval board and software, but everything works fine on the eval board when Digital Lock Detect window is set to High.

 

Because we want to use Phase Resync on these synths, we output all 6 words every time on 3 separate SPI buses which operate simultaneously and in synchronicity.  Total programming time is about 75us.  SPI decoding on the DSO indicates data is being sent correctly when compared to ADI programming software (except for W5, which isn't given, so we don't know).  I may put logic analyzer on Eval Board & see what ADI waveforms look like.  There must be a difference that matters somewhere!

 

I will post more and try to attach some files when I get to work, but I couldn't sleep, so I'm collecting my thoughts and writing this from home first...

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