I have an LM5119 based design, with interleaved operation (single output). The output is well regulated and stable and the switching waveforms look good. However, I notice that that side 2 of the converter stops switching when the input voltage goes above 50V. When the input voltage is reduced below 50V, side 2 starts switching again. Side 1 does not exhibit this behaviour. The EN2 pin is NC (so side 2 is always enabled). These tests are being performed at no load.
What are possible reasons that this could occur?
I ask, because this behaviour is eventually followed by catastrophic failure of the LM5119, and I am suspicious that this unexpected behaviour is a clue as to what is going on. Catastrophic failure always occurs at higher voltages, although I have now seen it at 50V input voltage. The switch node ringing is well controlled and does not go anywhere near the device's 65V rating.
Kind regards,
Andrew