On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann
wrote:

On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin
wrote:

Dry-slug tantalums across power rails are bad news. High dV/dT
literally ignites them; MnO2 is the oxidizer and tantalum is the fuel.

That's what I've read everywhere. Yet, I spent 10 years shipping
marine radios that were literally crammed with dipped and molded
tantalum caps on power supply rails with never a problem. The only
ones I've ever seen go up in smoke were reverse polarized (which
produced an impressive red glowing piece of slag and plenty of white
smog). Mostly, these caps were 25V caps on the 12V (nominal) power
supply lines and 16V caps on the 8 and 10V regulated lines. There
were also a bunch used in audio circuits.

The tantalum thing is very erratic. Some batches blow up, some are
fine.



However, we never used tantalums on the output of a switcher, where I
would expect problems. I guess using a tantalum in this 3.3V switcher
would qualify. However, at the time (1970's) the literature declared
that high voltage spikes were the culprit, not voltage slew rate.
Since these often appear together, I can see where there might be some
confusion.

I know for sure that tantalums sometimes blow up at below their rated
voltages, with no overshoot spikes. It's dV/dT, namely peak current,
that can ignite tiny particles of tantalum, which then burn in the
solid MnO2 electrolyte.



Derate them 3:1 on voltage, or use something else. Polymer aluminums
are good, and some come in a tantalum-like surface mount package.

The original cap is a 100uF 10v tantalum which is already 3:1 derated
in a 3.3 VDC power supply. However, that doesn't included voltage
spikes from the nearby inductor.

Could be. Or maybe there was a lot of dV/dT. Or maybe some other
failure mechanism.

Tantalums are just right for some things, but have to be used
carefully.

https://dl.dropboxusercontent.com/u/.../Caps/Bang.jpg

https://dl.dropboxusercontent.com/u/...ied_Tant_1.JPG