On 23 Sep 2015 23:14:46 GMT, joe hey wrote:

On Wed, 23 Sep 2015 14:11:36 -0400, rickman wrote:

On 9/23/2015 12:47 PM, krw wrote:
On 23 Sep 2015 15:24:36 GMT, joe hey wrote:

On Wed, 23 Sep 2015 07:22:29 -0700, John Larkin wrote:

On 23 Sep 2015 11:06:49 GMT, joe hey wrote:

On Wed, 23 Sep 2015 00:40:00 -0400, rickman wrote:

On 9/23/2015 12:20 AM, joe hey wrote:
On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin wrote:

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.


That's why in those cases a series resistor might be recommended
in order to limit the current spikes.

Add series resistance to a tantalum cap and you have just created
an electrolytic replacement.

Sorry, I forgot to mention to put the resistance in between the
power line and the tantalum.


But than it doesn't bypass the power rail!

No, we did it locally, every IC that was uncoupled with a tantalum, we
put a small resistor from the power rail to the tantalum and the
problem was solved. I clearly remember reading this advice in some
tantalum's datasheet or application note. As those IC's consume very
little, the DC voltage drop over the resistance was negligible, but
the reduction in current spikes through the tantalums was
considerable.
They didn't blow up anymore and neither did the IGBTs.

The point being that by adding the resistor, you've increased the "ESR"
of the cap(-resistor). You might just as well use an aluminum cap in
its place if ESR doesn't matter.

He is talking about this...

Vcc ---/\/\/\---+-------+
| |
IC =
| |
--- ---
- -
Not this...

Vcc ----+----/\/\/\-----+
| |
IC =
| |
--- ---
- -

Correct.

Nevermind!

I sit corrected. ;-)