# ADF5355 lock time / timeout values for low PFD frequencies

Question asked by cp4an on Jan 25, 2018

I use the ADF5355 with an PFD frequency of 1.024 MHz:

I measured lock time that is much longer than 3.5 ms. I like to lower the lock time so I changed Timeout values and measured minimum and maximum lock times:

 tlock_min [ms] tlock_max [ms] alc sl vc tl 2,28 3,6 5 2 2 2 3,1 4,6 10 4 2 2 3,5 4,9 15 6 2 2 3,42 5,38 20 8 2 2 4,22 7,04 30 12 2 2

To me it sees that ALC Timeout of 30 is only useful for high PFD frequencies like 61MHz.

I use following equations:

alc = 30                                = 30                                             [ADF5355 Datasheet rev.d, p.35]

sl = alc / 2,5                          = 30/2,5 = 12                              [ADF5355 Datasheet rev.d, p.35]

vc = ceiling(fpfd /2400000)   = ceiling(1024/2040)            = 1  [ADF5355 Datasheet rev.d, p.35]

tl = ceiling(fpfd * 50µs/alc)    = ceiling(1024000*50µs/30) = 2 [ADF5355 Datasheet rev.d, p.35]

To me it seems that ALC is to much for a PFD frequency like 1.024 MHz.

How can I compute ALC Timeout for my application to lower lock time with reliable lock detect?

You will find attached the ADF4355 Software config file for the ADF5355 Software.