From: Ingraham, Andrew (Andrew.Ingraham@compaq.com)
Date: Mon Apr 30 2001 - 07:02:26 PDT
> I had always thought +/- 5% was standard, which I guess is not.
> In such a case, what should be the tolerances on 5V,2.5V and 3.3V
> supply voltages.
In some logic families, the component spec range was +/-5% for
Industrial/Commercial grade devices, +/-10% for Military grade devices.
This is the range over which the component is guaranteed by the IC vendor to
work; not necessarily the actual power supply voltage range where that
component is used. If you are looking for the power supply voltage range,
start with the power supply's specs, then account for your I*R drops from
the sense point to the point of usage.
As supply voltages get lower, the tolerances, expressed as percentages, can
be expected to (but do not necessarily) increase.
Don't expect a symmetrical range either. I have seen +5% / -10%.
It all depends on where you look. For example, the 3.3V PCI system spec
calls for +/-0.3V (= +/-9.1%), but 3.3V AGP uses +0.15V / -0.2V (= +4.5% /
-6.1%), and 1.5V AGP uses +/-0.075V (= +/-5%).
The JEDEC standards for some 3.3V parts have a recommended operating range
of 2.7 to 3.6V (= +9.1% / -18.2%). Some JEDEC standards for 2.5V parts
specify +/-0.2V (= +/-8%), while another uses 1.8 to 2.7V (= +8% / -37%).
JESD8-7 for 1.8V parts has both a "normal range" (1.8V +/-0.15V) and a "wide
range" (1.2 - 1.95V).
Know your data sheets!
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