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PICList Thread
'low power oscillators'
1998\10\05@212546 by William Chops Westfield

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In view of the apparent facts that minimum power specs for PICs are based on
using an external osccilator, and that the typical power consumption of a
canned oscillator is ridiculously high, does anyone have any favorite circuits
(or just sources) for low power oscillators in the 32kHz to 4Mhz range?

(And did y'all notice Dallas's new to92 programmable oscillator circuit (no othe
r
parts required, 1% accuracy.)  Not what I'd call low-power, though.)

Thanks
Bill W

1998\10\06@101818 by Matt Bonner

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William Chops Westfield wrote:
>
> In view of the apparent facts that minimum power specs for PICs are based on
> using an external osccilator, and that the typical power consumption of a
> canned oscillator is ridiculously high, does anyone have any favorite circuits
> (or just sources) for low power oscillators in the 32kHz to 4Mhz range?
>
Statek makes a number of low-power oscillators, in a variety of
packages.  We've been using a custom part that they made for us, so I
can't give you even an estimate on what their standard parts cost.  I do
know that price goes way up for the better-trimmed parts.  The 32kHz
parts have a typical current consumption of 30 to 40uA at 5V and less at
3V.

The last time I looked, Statek didn't have much of a web site, so email
me privately if you'd like a scanned copy of their short-form data
sheet.

--Matt

1998\10\07@125744 by John Payson

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part 0 1221 bytes
|(And did y'all notice Dallas's new to92 programmable oscillator circuit (no oth
er
|parts required, 1% accuracy.)  Not what I'd call low-power, though.)

The PIC's power consumption when using a 32KHz crystal is not unreason-
able.  Perhaps lower-power operation could be obtained using an external
oscillator, but I've been quite happy with the LP mode.  I also somewhat
like the "secondary" LP oscillator found on some PICs; it allows a PIC
to run at 4MHz when it's active and yet still keep accurate time-of-day
when it's asleep (it powers up briefly every 2 seconds).

By no means, though, do I disagree with the notion that there may be
some advantages to using an external chip to drive/control the CPU
clock.  I've not really seen any I've liked too much, though (one thing
I would like would be a chip with a counter driven by a 32KHz crystal
and an output which could be selected between the 32KHz crystal and a
4MHz oscillator (crystal or RC).  If the 4MHz oscillator is an RC type,
it might also be useful to have a "putt putt" mode where the oscillator
runs for 4 cycles every tick of the 32KHz clock--for an operation speed
and power requirement between that of the slow and fast PICs.

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