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'battery-operated pics...'
1997\07\29@165613 by William Chops Westfield

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A couple question on the LP pics and other PICs operated from batteries.

1) For the PIC rated to operate on 3-6V, do they work reliably when powered
  from a 3V lithium battery (ie Duracell DL123?)

2) The LP parts are rated for a max clock freqeuncy of 40kHz.  I find it
  difficult to believe that a drastically different process is used for
  these, and assume tha 40kHz is just as fast as they'll go and still stay
  under then 18uA current consumption limit.  Is that correct?  If I'm
  willing to put up with higher current drain, will they run reliably at
  1 to 4 MHz?

Thanks
BillW

1997\07\29@171638 by Miller, Steve

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>1) For the PIC rated to operate on 3-6V, do they work reliablywhen powered
>   from a 3V lithium battery (ie Duracell DL123?)
<snip>

My experience with the 16LC622 is that they cannot reliably be operated from a
3V lithium battery at 4MHZ.  (The data sheet claims that they will work down to
2V at a max clock of 40KHZ., but I needed a minimum clock of 4MZ.)  With a 4MHZ
crystal some parts will not even startup with a fresh lithium battery (3.3V to
3.6 V).  My local FAE stated that the parts are speced at 4MHZ and 3.0 V.  Other
parts, will work fine at 2.4 V with a 4MHZ crystal.  I ended up using two 3V
lithiums in series to get any sort of reliable operation from the 16LC622.
Remember to test at the voltages you expect with a weak battery.  Good Luck.

----- Steve Miller

1997\07\29@181200 by Matt Bonner

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> 2) The LP parts are rated for a max clock freqeuncy of 40kHz.  I find it
>    difficult to believe that a drastically different process is used for
>    these, and assume tha 40kHz is just as fast as they'll go and still stay
>    under then 18uA current consumption limit.  Is that correct?  If I'm
>    willing to put up with higher current drain, will they run reliably at
>    1 to 4 MHz?
AFAIK, _running_ reliably is not the problem - starting up is.  I
believe LP versus XT versus HS establishes the value of the internal
feedback resistor between OSC1 and OSC2: higher frequency crystals need
more feedback current.

--Matt

1997\07\29@223811 by David W. Duley

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In a message dated 97-07-29 18:19:34 EDT, you write:

<<
My experience with the 16LC622 is that they cannot reliably be operated from
a
3V lithium battery at 4MHZ.  (The data sheet claims that they will work down
to
2V at a max clock of 40KHZ., but I needed a minimum clock of 4MZ.)  With a
4MHZ
crystal some parts will not even startup with a fresh lithium battery (3.3V
to
3.6 V).  My local FAE stated that the parts are speced at 4MHZ and 3.0 V.
Other
parts, will work fine at 2.4 V with a 4MHZ crystal.  I ended up using two 3V
lithiums in series to get any sort of reliable operation from the 16LC622.
Remember to test at the voltages you expect with a weak battery.  Good Luck.

----- Steve Miller >>
Hello Steve and all,
I did a project a while ago that was faced with the same problem.  I solved
it by using a MAX859 (I think that was the part#) Switching mode regulator.
It accepts down to 1V in and provides 3.6 volts out at 50ma.  It is a 8 pin
SO8 package and all you need is a 47mh inductor (This was about a 1206 SMD).
The device had to be small because it is wrist worn by astronauts.  It also
has a battery low output that can be monitored by the PIC.  We used a 1600mah
lithium primary cell that was 1" X .7" X .4".  The device had to run for 5
days on a single battery.
Hope this helps
Dave Duley
V.P. DreiTek Inc.

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