Hello,
I have implemented a simple 5V buck converter using the LMR14030, however it is behaving strangely in various ways. Here is the schematic for my converter:
1st issue: Over current protection seems to be triggering when I switch in a 10 Ohm load. The scope shows a drop in output voltage to 1.32V, which is aproximately 25% of the regulated output. The datasheet states in 8.3.9 that the switcher will drop switching frequency to 25% of the initial setup, I'm not sure if this should lead to the output voltage drop I'm observing.
2nd issue: Soft start time is not behaving according to what was expected.I have used a 27nF cap at the SS pin, which according to the datasheet will give me a ramp of 6ms on the output when I turn on the input - However, I'm observing a 936ms ramp time, almost an entire second. I tried switching the soft start cap: When I used 100pF, the startup by VIN took 19ms. After using a 100nF cap, I observed a 14.75ms ramp. None of these values make sense according to equation (15) of the datasheet.
So, I've kept the 100nF soft start cap, and measured the output after connecting a 10 Ohm load. The output oscillates, as if trying to go up and drive the load, but then it falls as if a failure mechanism were driving it back to 0V. Here is the scope of the output with the 10 Ohm load connected. We can observe a low frequency oscilation of aprox. 150Hz.
What am I doing wrong here?
Thank you for your support.
Leonardo Rossi
