EV-ADF4159EB3Z Eval vtune range

Hi,

I want to use an ADF4159EB3Z eval board with an external VCO with a vtune range or 0-5 volt for 2400 Mhz RF output.

I've populated the loop filter according to AdiSimPLL spec for the correct PLL and my custom external VCO.

I powered the OPAMP with 15 volt but unfortunately, the vtune output is stuck at 15 volt even if I used a 5 volt VCO spec so it is out of range ?

Not sure what i've done wrong since my loop filter components seem all ok, I don't now what I need to do to reduce the vtune output of the eval board so it can be used with my own VCO ?  

Thanks