LiPoly or coin cell power for 3.3V MCU?

FlyingFishFinger

Hi-
I'm looking for a hypothetical board-mount power solution for a very small, low power MCU. I was looking at either a single LiPoly cell or a small stack of (rechargeable?) coin cells.
If I'm running a 3.3V micro, is an LDO reg good enough? As far as I know LiPoly's can go down to 3.0V. If that's the case, is there a better way to power something like this?
Thanks

Rafael

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UC Berkeley '12 EECS
CalSol: UC Berkeley Solar Car
http://calsol.berkeley.edu
KJ6AWU

Peter KG6LSE

LiPoly needs a smart-er kind of charger so It does not turn in to C4 . a normal NiCd 120mAH Coin cell array is IMHO more forgiveing to charger Specs . Still with such a small mAH capaciy I would use a Very tight CC and CV circuit to keep the cells from also poping ..

In " float " use off a PSU rail a simple well sized Resistor could be used with the NiCd cells //It the charge rate is less then C/30..


In a ideal world a "Simple switcher " would be a more Efficaint choise . and cause your useing super tiny Coin cells you dont have much extra Power to waist as heat ..

I have seen Drop In LM78XX equliviaint Switchers .I forget the company name but there In Nuts and Volts
.

In Gnd Out Simple little things ...

Peter KG6LSE

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"Carpe Ducktum" "seize the tape!!"
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LOL

FlyingFishFinger

I'm not worried about charging, that can be done off board with whatever circuit is needed. I'm looking for the smallest cell I can run a micro and, more importantly, a bluetooth / wireless chip off.

R

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UC Berkeley '12 EECS
CalSol: UC Berkeley Solar Car
http://calsol.berkeley.edu
KJ6AWU

Peter KG6LSE

then LiPoly will do [noparse]:)[/noparse]

Peter KG6LSE

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"Carpe Ducktum" "seize the tape!!"
peterthethinker.com/tesla/Venom/Venom.html
Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway. —Tanenbaum, Andrew S.
LOL

viskr

While Bluetooth is possible with a small coin cell, wireless like Xbee requires much more power. The largest coin cell can only deliver in the range of 4-5mA depending on chemistry.

Xbee power average can be low, but expect 40 mA while receiving or up to 200 mA when transmitting.

A low dropout regulator is probably best, as the efficiency of turning 3.7V into 3.3 is about the same as a switcher. What a switcher could do is to provide 3.3V as the battery discharges below 3.3V. But this probably isn't needed as things like Xbee will run at lower than 3.3V. But in any case your circuit should be sending out "come charge me" messages at that point.