QUESTION ABOUT ADF4159 AND ADF5901

Hi, I'm using ADF4159 and ADF5901 to generate 24GHz ~ 24.25GHz FMCW signal. My question is: Have you ever measure the maximun Fdev per step ? I want to get a high slope of a single sawtooth burst. My reference frequency is 50M and I set Ref doubler so that my PFD is 100M. Then I set CLK1 = 1 and CLK2 = 2 to get minimum time per step = 0.02us. BUT when I set the Fdev = 30k to get a slope of 15MHz/us, the PLL can not lock. SO I want to know how can I get higher slope? Can I change the bandwidth of LOOP FILTER ?What's the maximum slope of ADF4159 & ADF5901?