From: Phil Hobbs
Subject: Re: Drift/Worst Case calculations of SMD Chip Resistors
Date: Wed, 02 Oct 2002 11:29:24 -0400
Organization: IBM T. J. Watson Research Center
NNTP-Posting-Date: 2 Oct 2002 15:29:25 GMT
X-Mailer: Mozilla 4.61 [en] (OS/2; U)
Klaus Vestergaard Kragelund wrote:
> I would normally just use the 1% spread and calculate the drift coming from
> the temperature coefficient. But is this enough - several other factors are
> described in the datasheet:
> Shelf life, short term overload, climatic, rapid temperature change,
> soldering and vibration.
> My question is which of these factors will make permanent changes to the
> resistor value?
> Also the "Temperature rapid change" isn't that a bit dubious - rapid is
> pretty relative? (from person to person)
> And finally what would you guys from experience use for your worst
> case/drift calculations? - load, soldering and vibration - or all of them?
I wouldn't use these particular resistors in any circuit where a 10%
change would make it stop working. Those specs remind me of the old
carbon composition days--5% permanent change due to overvoltage, 2.5%
for soldering, 2% for 1000 hours at rated load,... in a 1% resistor?
give me a break.
If you need accuracy, stick with metal film devices--ordinary RN55C
models are down in the 0.1% range for all those effects, and garden
variety 0805s aren't much worse than that.
IBM T. J. Watson Research Center
Yorktown Heights, NY