we have designed a supply system for a FPGA with the LTM4620A power module, for generating a output reference of 0.95V / 26A with the parallel mode (both outputs are tied together) from a 12V input source. The circuit is showed in the image below.
Simulation in LTSpice works correctly, however, we are experimenting a switching noise in the output voltage. Here I attached some photos:
Some relevant observations:
- Output average voltage is lower than expected. The resistor 102k should fix the output value around 950mV, however the average value is 761mV
- Output voltage presents a switching noise, near from the programmed frequency (120k sets a 500khz conmutation frequency)
- INTVCC value is correct and without noise.
- TRACK/SS presents a negative value!!!! (This is not seen in simulations). Average value -419mV
- VFB also presents the switching noise, average value 460mV and 276mV peak-to-peak.
- Rise time is different from desired value (around 50 us). It seems to rise as fast as possible.
I appreciate any help.