We have a design with an Arria 10, powered by 12 Enpirion POL converters.Input power is 5VDC, and sequencing is controlled by a Lattice semi power manager. The POL converters are segregated into several branches (core voltages, I/O voltages, etc.). Enabling of the branches is controlled by switching the 5VDC input power through N-channel MOSFETs. The design includes four EN6340 switching regulators, in addition to eight other Enpirion parts (EN5311, EM2130, EN5322, EN6360). The EN6340s exhibit undesirable start-up transient behavior (5VDC output spike); the other devices all start up cleanly, with no overvoltage transient.
Details are provided in the attachment.
We are so sorry for late response.
I have received your case yesterday through Andrew too, this is not stability issue and it is related to the part output capacitors and the SS capacitor will not cause that too.
This issue it seems related to the PMOS (high side MOSFET) turn on for some time during the start up.
Actually this device can support very high input voltage slew rate without affecting the PMOS gate drive.
But we can try to check that point, so if it possible to mount a 500Ohm between pin 18 (pin 18 is NC pin) and pin17 (PVIN pin) and check if this solve the issue.
Also there is something weird where all EN6340 in your board have the same issue.
One of the way to check if your board has an layout issue or not is to mount a good know EN6340 from one of the Demo board or drop in board (if you own any of them) and test if the issue still there or not.
Also we would like to do FA on that samples that have the issue, so if you could help to send 2pcs from that part and have that issue for more investigation.