Re: How inaccurate is a 555 or 7555 REALLY?

On 2 Dec 2006 12:42:16 -0800, the renowned "WildIrish"
<wildirishtiming@xxxxxxxxxxx> wrote:

Two questions. I'm a novice with 555's, some minor experience.
I need to develop a very small 555 timer circuit that runs on a 1.5v AA
battery.

1. Which 555 is out there that runs that voltage and small package?
(smd would
be fine as long as It has solder pads i can solder to under microscope)

TLC551, SOIC-8. Not really small.

2. I plan to calibrate it up to run at 420hz. I'm still unsure if 555
is accurate enough,
I have read some Maxim and National spec sheets and I'm unclear on
accuracy.

How inaccurate is it truely in percentage at 420hz? I really can't
afford more than .1%
inaccuracy, is there a way to reach these levels of accuracy using 555?
special
R and C to make that happen?

Expecting much better than ~1% over reasonable temperature changes,
supply voltage changes etc. is probably optimistic. Not only the chip,
but capacitors and other parts will change.

The only reason I want to use 555 is it seems very tiny (space is an
issue) and
rather simple, but maybe there's another more accurate way? I'm open
to suggestions if they use minimal # of components.

You could step the 1.5V up to 3V using a switching regulator and then
use a CMOS chip or a microcontroller with a crystal timebase, and
avoid the calibration.

Thanks a bunch for all your help in advance!
-Brendan


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
.

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