Hello forum:
We just got our new design prototypes back in this week and are working on bringing them up and debugging any issues that we run into. We are having some power cycling issues and would like to solicit some TI assistance in debugging this problem. We are using a TI regulator on this board, the LM3150MHX/NOPB. We used the WEBENCH tool on TI’s website to help with the design of this circuit, but there is still a problem somewhere. Please see the scope trace in the attached TEK00000.PNG file. This is a capture of the output of the regulator, across the output capacitor C363 in our design. The regulator appears to start up for 4-5ms and then shuts off for a while (~25ms) and then turn on again briefly (2-3ms) before it turns off.
I’ve attached the original WEBENCH design report as well as the relevant page from our schematic for this circuit. There are some differences in terms of parts selection but I can’t identify a change in particular that is causing this problem.
We did go back and run through some of the calculations in the datasheet and most of them look in line with what WEBENCH recommends. One that seemed pretty far off to me was the value of Cff which is listed as a 1.5nF cap in the WEBENCH report but our calculations have it as a 78pF cap, but we tried moving to a smaller value cap (68pF) and it didn’t make any difference operationally.
Any feedback or input is welcomed and appreciated!
Thanks again!
Paul
