Tool/software:
Hi,
When starting to eload ( current slew rate 2A/us ) with approximate ~5m loom, LM5066i doesn't start and power limit protection doesn't trigger and in some point this can break FET. Look pictures below.
I think what happens is :
1. Output ( midpoint in picture ) start to rise and when voltage is more than uvlo of eload, output current start to rise with Slew rate set to eload.
2. Current can rise to ~3A after which eload voltage is less than its uvlo and it will turn off ( Eload voltage = Midpoint voltage - Loom resistance * Output current )
3. When the eload is removed, transistor Q6 current is more than needed to soft start 20u output cap. That "extra" current has to go output caps and that's why we are seeing short jump in output.
Because of output jump up, gate is also jumping up, but not so much because of extra soft start capacitor in the gate. This means transistor Vgs will drop to reduce current.
Also after output jump up, you can see output and gate jump down, which means pnp circuit will active and charge soft start capacitor back to starting point.
4. 1-3. will repeat until transistor breaks.
I removed external pnp discharge circuit and after that startup is fine. There are always couple of similar oscillations as below but finally starts. This makes sense because extra capacitance on the gate is not anymore discharging and will collect charge until start is possible.
Would you have some good ideas to fix the issue: i don't want to add more output capacitance, we cannot make soft start anymore faster and pnp circuit you are needing...
