Problem using LM5069, the Voltage Hot Swap / Inrush Current Controller

Hi Xiao,

Based on the waveform, it looks like the device is cycling on/off.

When the device initially turns on, it will appear like a current load step.

Due to the amount of inductance from the surge generator, the circuit will appear to be like an LC circuit with a load step.

This will cause oscillations like shown above. When the LM5069 turns on, the input capacitors (C2, C3, C4, C5) are insufficient to sustain the power going to charge the output capacitors. The supply from the test generator is getting blocked by the input inductors. So the capacitor C5 will collapse and turn off the LM5069. You can see from the negative peak of the oscillation, it dips below the LM5069's UVLO and the LM5069 may shut down at this point. Then the LC ringing should dampen (which they appear to do). However, once they begin to dampen, we see they begin again. This may be the point where the LM5069 turns back on and injects another load step.

So this cycle will continue to repeat and the LM5069 turn on and off.

If you take a waveform of: VIN pin of the LM5069 IC, GATE, UVLO then we can double check that this is the behavior.

A couple of potential options to get around this:

1. Bypass the inductors (with a wire) in order for the LM5069 to turn on. Then remove the bypass wire and begin the surge test.

2. Increasing the capacitance of C5 may help sustain the LM5069 VIN to not collapse when turning on.

Thanks,
Alex