Hi all,
I was hoping for a bit of help with my ADL5317 design, as I feel I have tried everything to get to the bottom of why it isnt working as expected.
The Issue
So the issue is that when I power up the ADL5317 and VPHV is 75V the IC gets very hot in very short period of time and wont follow the voltage on VSET. However on the PCBs I had made I have briefly had some of the boards to work for a short period of time, as in I tested one of the boards and it followed VSET and the IC didnt get hot, I then powered everything down left for 1 minute came back and upon powering on again the IC now gets hot and wont follow VSET.
Things I have tried
1.) If I lower the voltage of VAPD the IC does stay within a more reasonable temperature if VAPD is around 40V and below.
2.) Currently VSET is fed from output of an op amp, so I have tried bypassing the op amp and supply VSET voltage directly to the the VSET pin
3.) I have tried a different op-amp with lower bandwidth as once proped with oscilloscope the output of the original op amp was noisy as was acting as an antenna.
4.) I have tried heatsinks on the IC
5.) I have tried not populating the DC-DC converter that creates the 75V and instead supply 75V to the PCB directly and I have measured the DC-DC output for noise.
So overall I am confused as what is wrong, I largely just followed the reference design given in the datasheet (Figure 23):
https://www.analog.com/media/en/technical-documentation/data-sheets/ADL5317.pdf
My schematic is shown in the image below
