Chip temperature ratings?

[Glenn Ashmore]

What happens when a chip is colder than its rating? Say I have a choice
of 2 versions of the same chip. On rated for 0-70C for $.76 and the
other rated -4-85C for $4.96. The non-critical circuit will be in a box
outside where once in a VERY rare while it may be called on to operate
at -5C. Is it not going to work or just maybe not going to work?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Gareth]

Glenn Ashmore wrote:

What happens when a chip is colder than its rating? Say I have a choice
of 2 versions of the same chip. On rated for 0-70C for $.76 and the
other rated -4-85C for $4.96. The non-critical circuit will be in a box
outside where once in a VERY rare while it may be called on to operate
at -5C. Is it not going to work or just maybe not going to work?

I can't imagine any chip suddenly stopping completely when the

temperature gets to 0C, but it may not meet its spec in some way, for
example a voltage regulator may have a higher voltage drop out than
expected, or an oscillator will be a bit off frequency. What exactly is it?

The other thing to consider is that though the outside temperature is
-5C the temperature in the box will probably be a bit higher if the
electronics is running.

It will probably work.

Gareth.

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[Glenn Ashmore]

The chip that has the largest price difference (about $4 difference at
Digikey and back ordered)is an RS422/485 transmitter/receiver that links
a cockpit lighting control to a digital switch in the cabin. All the
other -40C chips are fairly cheap and the PIC goes to -55C.

I have to say that I have added a manual override and it is highly
unlikely that it would ever see -5C as I am a thin blooded South Georgia
sailor who has no intention of sailing north of the Mason Dixon line
between September and May.

Gareth wrote:

Glenn Ashmore wrote:

What happens when a chip is colder than its rating? Say I have a
choice of 2 versions of the same chip. On rated for 0-70C for $.76
and the other rated -4-85C for $4.96. The non-critical circuit will
be in a box outside where once in a VERY rare while it may be called
on to operate at -5C. Is it not going to work or just maybe not going
to work?

I can't imagine any chip suddenly stopping completely when the
temperature gets to 0C, but it may not meet its spec in some way, for
example a voltage regulator may have a higher voltage drop out than
expected, or an oscillator will be a bit off frequency. What exactly is
it?

The other thing to consider is that though the outside temperature is
-5C the temperature in the box will probably be a bit higher if the
electronics is running.

It will probably work.

Gareth.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[CFoley1064]

Subject: Chip temperature ratings?
From: Glenn Ashmore gashmore3@cox.net
Date: 2/25/2004 4:23 PM Central Standard Time
Message-id: <Wm9%b.3304$Ri6.889@lakeread04

What happens when a chip is colder than its rating? Say I have a choice
of 2 versions of the same chip. On rated for 0-70C for $.76 and the
other rated -4-85C for $4.96. The non-critical circuit will be in a box
outside where once in a VERY rare while it may be called on to operate
at -5C. Is it not going to work or just maybe not going to work?

--
Glenn Ashmore

One of the things you get with the extended temperature range is more
resistance to humidity and moisture getting into the chip (look at the side of
commercial chips -- you'll sometimes see the metal from the leadframe sticking
out the east or west sides of the chip).

Most of your stuff has to do with marine applications anyway, so you probably
already use a conformal coating over your boards to prevent corrosion. If
you're planning on occasional extremes of cold, you might want to consider a
conformal coating to reduce the chance of humidity or condensation (which you
will get with excursions below 0C, possibility of salt in the air making things
orders of magnitude worse) getting into the chip. Apart from that, it's not an
engineered solution, but it should work fairly reliably.

Good luck, and fair weather, sir.
Chris