piclist 1998\10\07\125744a >
Thread: low power oscillators
face BY : John Payson email (remove spam text)

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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 oth
|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.


See also: www.piclist.com/techref/timers.htm?key=oscillator
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