Re: Predictive failures

"John Larkin" <jjSNIPlarkin@highNONOlandtechnology.com> wrote in message
news:uhpv1jd4b0cd20haudbsb3dneut5dap4ka@4ax.com...

On Tue, 16 Apr 2024 20:23:46 -0700, John Larkin
<jjSNIPlarkin@highNONOlandtechnology.com> wrote:
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On Tue, 16 Apr 2024 21:16:45 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
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"John Larkin" <jjSNIPlarkin@highNONOlandtechnology.com> wrote in message
news:p47u1j1tg35ctb3tcta5qevsfnhgnpcrsg@4ax.com...

On Tue, 16 Apr 2024 13:39:07 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
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On 17/04/2024 1:22 am, John Larkin wrote:

On Tue, 16 Apr 2024 09:45:34 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:

On 15/04/2024 18:13, Don Y wrote:

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Yes I've seen that a lot.
The power rails in the production product came up in a different order
to
those in the development lab.
This caused all kinds of previously unseen behaviour including an
expensive
flash a/d chip burning up.
>
I'd have it in the test spec that any missing power rail does not cause
issues.
And any power rail can be turned on and off any time.
The equipment may not work properly with a missing power rail but it
should
not be damaged.

>
>
Some FPGAs require supply sequencing, as may as four.
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LM3880 is a dedicated powerup sequencer, most cool.
>
https://www.dropbox.com/scl/fi/gwrimefrgm729k8enqrir/28S662D_sh_19.pdf?rlkey=qvyip7rjqfy6i9yegqrt57n23&dl=0
>

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Ok that doesn't surprise me.
I'd want to be sure that the requirement is always met even when the 12V
connector is in a position where it isn't sure whether it's connected or
not.
Or rapid and repeated connect/disconnect of 12V doesn't cause any issue.
>

>
We considered the brownout case. The MAX809 handles that.
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This supply will also tolerate +24v input, in case someone grabs the
wrong wart. Or connects the power backwards.
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>

>
Another hazard/failure mode happens when things like opamps use pos
and neg supply rails. A positive regulator, for example, can latch up
if its output is pulled negative, though ground, at startup. Brownout
dippies can trigger that too.
>
Add schottky diodes to ground.

I've seen many a circuit with pos and neg supply rails for op amps when a
single rail would have been fine.
In one case the output went negative during startup and the following device
(a VCO) didn't like that and refused to start.
A series diode was the easiest solution in that case.