We used two of your LTM4700 in parallel to supply up to 200A at 0,85V to an FPGA. However, a large oscillation (larger 100mV amplitude) emerges, when we use more than a single phase of the LTM4700.
When using all four phases available in the two LTM4700, we get an oscillation frequency of 17.8 kHz. When using only the two phases of the same LTM4700 (no matter which one), a 9.4kHz oscillation forms. The mean of this oscillation is exactly the desired 850mV output voltage. We assume it is some kind of instability, as it is nowhere near the switching frequency.
We checked the design for stability in LTPowerCAD and also simulated in LTSpice, but there was no hint to the source of that oscillation. Unfortunately, we can not buy a multi-phase evaluation board due to the availability. We have connected the supplies as is demanded in the load sharing application in the datasheet (Figure 48) and stated on page 69/70.
We tried increasing the output capacitance by adding more capacitors, we tried different values for the internal Rth, but the oscillation persists.
Is this oscillating behavior known? Can you tell us a reason for that?
Thank you and best regards
