Other Parts Discussed in Thread: TPS62150
Hello,
I've just started testing a design I'm using with a power stage based off the LM5141-Q1. There is also a TPS62150 providing a secondary rail.
My design requirements are 24Vin, 3.3V out @ 2A max, 1.9V out @ 1A max. Here is my schematic as well as the WebBench schematic that was generated for this case (they should be identical),
So I'm having this issue, when I hook up a DC load to test the power stage (hook up to the 3.3V output) and draw any more than ~0.1A, the power output cuts off and then periodically tries to restart (roughly 15Hz), as seen here:
It turns out, after some examination, that the inductor I am using only has a saturation current of ~.25A, and a current rating of ~0.3A. This was pretty surprising seeing as this was one of the inductors that WebBench listed as an acceptable alternate to that in the PDF. Even so, I should have looked more closely.
It runs quite hot as well, about 71 degC with ~0.5A of current (measured using Rsense). Not altogether unexpected.
Interestingly, when I run the same design again on WebBench I get very different values of inductors. For the same input/output conditions, sometimes it suggests a 3.3uH inductor @ 2.2MHz, sometimes at 15uH inductor at 440kHz, sometimes something else entirely. And of course with different compensation networks.
So my question is: what is the primary cause of this behavior? Is this a stability problem, or an inductor saturation problem? I.e. if I had the same value inductor with a higher saturation current would this problem go away? Or is the problem a control-loop stability problem that will require tuning the compensation network or making other changes? Is failure to regulate as the inductor saturation current is reached a common behavior? I'm about to go through the full design process for the LM5141-Q1 but I want more experienced eyes to make sure I'm not overlooking something that may be an issue.
Thank you for any help!
