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'REAL current draw at 32KHz'
1999\07\29@234130 by Russell McMahon

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Anybody got some practical real-life current drain figures of PIC
designs at 32KHz?

Yes, I could measure a few circuits but use experience may count for
more than my few measurements or even the spec sheet typical and max
figures.


This is a very very simple application -
1 pin output 50ms pulse every two seconds.
Crystal accuracy required.
Replaces obsolete IC.

Sounds like a job for a 12C504 :-) but it looks like a 12C508 will
do.
16C505 may be cheaper but extra physical size is a nuisance.






Russell McMahon

1999\07\30@092507 by Jim Hartmann

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      How about 30uA at 192kHz, 16C622a, watchdog enabled, brownout
      disabled?

1999\07\30@094334 by Barry King

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Russell,

> Anybody got some practical real-life current drain figures of PIC
> designs at 32KHz?
A 16LC76 based design: 32 kHz tuning-fork rock, 5 V power supply/

Quiescent current of the whole PCB (average of first few hundred
production units: 58 microamperes.  About 10 uA of that is peripheral
circuitry that is on, and sundry leakage currents.

That an LC 76, mind you, and you can get lower on on other parts.

------------
Barry King, KA1NLH
Engineering Manager
NRG Systems "Measuring the Wind's Energy"
Hinesburg, Vermont, USA
http://www.nrgsystems.com

1999\07\30@111512 by Barry King

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Russell,

> A 16LC76 based design: 32 kHz tuning-fork rock, 5 V power supply/
...
> That's an >>>LC<<< 76, mind you, and you can get lower on on other parts.
...

Oh, yeah, I forgot to say: that's with LP oscillator of course,
and with Watchdog ON, but Brownout detect OFF.

Brownout detect is obviously intended for AC fail and not for low
battery, because the BOR itself draws 400 uA!

------------
Barry King, KA1NLH
Engineering Manager
NRG Systems "Measuring the Wind's Energy"
Hinesburg, Vermont, USA
http://www.nrgsystems.com

1999\07\30@194437 by Brent Brown

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Russel,

> Anybody got some practical real-life current drain figures of PIC
> designs at 32KHz?

Scratching my memory to remember exact figures but I used a
PIC16C63 with OSC1=4MHz resonator & OSC2=32.768kHz
crystal.  Sleep (32kHz osc continues) for 2 seconds then wake up
briefly to increment software real time clock, check alarms and go
back to sleep.

WDT, POR etc on but brownout detect definitely off, about 25-30uA
average.  Or I think about 15uA with the WDT off.  I used a Seiko
low power & LDO voltage regulator and reset generator which
accounted for only a few microamps.

The biggest current draw was self discharge of the nicads!

Brent

Brent Brown
Electronic Design Solutions &
HI-TECH Software Sales
16 English Street
Hamilton, New Zealand
Toll Free: 0508 HITECH (0508 448 324)
Ph/fax: +64 7 849 0069
Mobile: 025 334 069
eMail:  spam_OUTbrent.brownTakeThisOuTspamclear.net.nz

1999\07\31@034359 by Hans Blichfeldt

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At 01:33 PM 30/07/1999 +1200, you wrote:
>Anybody got some practical real-life current drain figures of PIC
>designs at 32KHz?
>
>Yes, I could measure a few circuits but use experience may count for
>more than my few measurements or even the spec sheet typical and max
>figures.
>
>
If only oscillator runs, the current consumption will depend on
- supply voltage
- capacitor/resistor values used for osc.
- crystal used for osc.

A 16C54 (or 71) may use 18 uA at 4 V, 30uA at 5.2 V.
This could be cut with a selection of caps and resistor
specific for a certain voltage. - You would
then risk start-up problems or stops at
other supply voltages.

Best regards,

Hans


'REAL current draw at 32KHz'
1999\08\02@000844 by William K. Borsum
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At 01:33 PM 7/30/99 +1200, you wrote:
>Anybody got some practical real-life current drain figures of PIC
>designs at 32KHz?
>
>Yes, I could measure a few circuits but use experience may count for
>more than my few measurements or even the spec sheet typical and max
>figures.
>
>
>This is a very very simple application -
>1 pin output 50ms pulse every two seconds.
>Crystal accuracy required.
>Replaces obsolete IC.
>
>Sounds like a job for a 12C504 :-) but it looks like a 12C508 will
>do.
>16C505 may be cheaper but extra physical size is a nuisance.

Did this with a 508/509 a while back.  works great.  Run the processor at
3.3 volts for about 9 uA of draw.  25 uA at 5 volts.  HUGE delta?
Need to interface to 5 volt logic?  look at the (I think) LVC series of
CMOS--will run at 3.3 volts but take inputs to 7 or so.  Great stuff.

In general my 32 KHZ designs seem to run pretty consistently in the 45-60
uA range when all is said and done with regulators and all the needed
peripheral support.  Telcom TC-55's are fantastic regulators.  Be sure to
use CERAMIC caps!  even in the 1-4 uF range.  Tantalum leakage is
hideous--a couple of uA per cap are not unusual.  Mouser now carries 1 uF
ceramics--temp co is awful though.  The good ones are about $.50 or so and
available only in full reels.  Would consider splitting a reel if there is
any interest.

RE the crystal:  The short the time interval the greater the jitter
(difference in absolute times between pulses).  However, the average will
be as good as the crystal.

Had some REAL problems getting the 509 to oscillate in newer revisions.  If
you have ANY problems, try sticking a 100K CARBON COMPOSITION (NOT metal
film) resistor in series (see the data book for the location) and you
should start up every time.  Sometimes a little noise is a good thing.

Kelly

****************************************************************************
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William K. Borsum, P.E.
OEM Dataloggers and Instrumentation Systems
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