Operation of PICs from low voltage
Russell McMahon email (remove spam text)
Still coming to grips with this new fangled system - gotta put : after PIC
they tell me to ensure all the pure PIC people see it .... mumble, mumble
... try again.
Based on actual experience. - What is the lowest Vdd at which a 16F84 will
operate (including occasional EEROM read/write) reliably using an RC clock
at about 1 MHz?
Yes. I know what the data sheets say.
Yes, I know the answer is try it and see.
Yes, I know the results will vary.
No - I don't (yet) know what other people have tried and found works.
Based on random aged 16F84 data sheet:
- The std 16F84 is specified to operate at a minimum Vdd of 4.5 V
- The 16LF84 is specified down to 2 volts
I am building a small 16F84 device where portability and battery life is
important (wearable aid for a disabled person), Essential aim is to drive a
beeper subject to certain constraints - irrelevant to following. Device will
be carried in top pocket / worn on cord around neck / clipped to clothing so
user but hopefully few others can hear the occasional beep. Another variant
may drive a pager vibrator instead.
I am running a 16F84-10 (10M parts happened to be in parts drawer) .
This runs happily with physically small 3.6V 80 mAH NiMH battery and RC
clock (33K, 18pF) at 1MHz osc = 25o KHz PIC basic instruction rate.
This is very adequate for my task.
At 3.8V it draws 250 uA
At 2 volts it is still running and clock frequency has not moved markedly
and draws 100uA
At 1 volt it is STILL running but clock is MUCH slower (~ factor of 10?) and
draws under 10uA (!)
I don't need to run at 1 V but ability to run at 2V is interesting.
I haven't tried eerom read/writes yet at 2V.
What have other people found about low voltage operation of "standard"
Is this perhaps another example of Microchip 'select on test"ing parts and
many std parts are in fact capable of low voltage operation?
Yep - I could (try to) buy some 16LF84's but ...
See also: www.piclist.com/techref/power.htm?key=voltage
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