A few years ago, I did a design that had four LM21215A-1 supplies and one TPS56121 supply. A general
board revision prompted me to review the design parameters for all of the supplies. I ran, or rather tried
to run, the designs through the current Webench and have had no end of problems:
a) erratic behavior for webench for both parts,
b) errors in webench itself (for example, advanced options doesn't work correctly for frequency or
ceramic capacitors in advanced options for either part)
c) you can't set the device frequency in the TPS56121 or 221 design page
d) modify operation point doesn't allow you to modify
e) LM21215A-1 (or other LM2121x variants) load transient SIM is very flaky - sometimes it runs and
sometimes it doesn't. When it does, it often gives ludicrous transient values in the 100s of mV
f) if SIM fails in the LM21215 load transient, it will sometimes replace the current design with the startup design, deleting all changes
g) transient load SIM appears to pick a starting point for its test before the power supply has reached initial steady state. It isn't
possible to tell SIM to wait until steady state has been achieved. The max initial delay is less than soft start delay. Plus., if
you choose a soft start of, say, 1ms,. the parts take a few msec to actually start the soft start up phase
h) edit schematic creates a new version of the schematic in a standalone design, not in "CC", making it useless.
i) custom parts are newer saved - there is no customer part library - so you have to reenter the parts. Since webench
often resets itself, you have to thus reenter everything every time.
j) webench models do not match quickstart in any comprehensible way
k) webench has no way to specify transient limits and thus no way to optimize transient performance. SIM cycles
are painful way to try to optimize and in the case, especially for the LM21215, hazardous to the design at hand
l) webench has no save button. You can never be certain that your actual design has been correctly saved. And, if
you go into the design at a later date, webench will modify without notice or permission. You can copy a design
but you have to go into the design to do that, and webench may tinker with the design before you can dupe it. There
should be an external copy.
m) there is no way to truly archive or even export/import a design
n) TI has no active customer support for this software. I have asked and asked and asked.
