adf4158 muxout

I'm using ADF4158 in my FMCW radar and tring to generate a continous sawtooth waveform.And I am sure the SPI writing timing meets the requirements in the datasheet.But the time may be more longer than the datasheet given out.For example, the LE set up time is 20 ns min,and the time I set is around 2us.

Now I can get the ramp complete signal on MUXOUT pin which is the same as the frequency I have set,but I can't get the vtune and also I can't get the transmit wave from the Radar.

I'm wondering whether the ramp complete signal means the regesiters have been set successfully?If it is,so why can't I get the vtune like a sawtooth wave?Is thers anything wrong with VCO?How can I get the wave?

Or the MUXOUT of complete signal can't mean the right set of regesiters?

Whether the too longer time of LE effect the operation of ADF4158?

Thanks a lot.