I've used the HMC980 several times and it's a great chip. With the amp HMC487 I can not get the drain to turn on if the gate (from HMC980) is connected. If I add a separate negative supply to the amp gate Vd will turn on, but of course the automatic gate adjustment for the programmed current does not work. Also the safe biasing sequencing will not then work.
The HMC980 datasheet spec's for the HMC487. Any ideas why the gate connection to the amp is stopping the switching - I was wondering about excessive current sinking or something? I have tried removing most of the decoupling capacitors on my test boards already,