AVR-Chat

Hi Reza,

Try looking at e.g. Seiko Instruments homepage
(http://www.sii-ic.com/en/param_chrt.jsp?subcatID=5). 
There are a lot of semiconductor makers on the marked, which makes
Li-Ion protection chips.

Once lower discharge voltage is surpassed, the chip shuts the battery
down (via external FET). The battery is turned back online again, when
put into a charger. 

This way you also protect the battery from being shorted for a longer
amount of time.

Just some generic Li-Ion information for you :o)

Cheers,
Jesper Holst



--- In AVR-Chat@yahoogroups.com, Reza Naima <reza@...> wrote:
>
> So I'm looking at deploying a device with a Li-Poly battery on board.  
> The voltage of a fully charged battery should be 4.2V, and will drop 
> over time.  My application calls for a 3.3V source, and I was
looking at 
> using a LDO voltage regulator which has a *fault line to indicate when 
> the voltage out is not correct (i.e. below 3.3v).  At this point, I 
> would like to shut down the device, but I'm not sure how to do it.  If 
> the device shuts down, I expect the voltage to rise above 3.3v, the 
> device will power on again, the voltage will drop, it will shut down 
> again.... et cetera... and just oscillate using up more battery and 
> possibly permanently damaging it. 
> 
> This would seem like a common problem.  Has anyone else run into it -- 
> and if so -- what solutions are available?  I can shut down a lot of
the 

> peripherals on the board, but there will be a number of components that 
> I can't shut off and I don't want to run into the situation where the 
> battery is bled dry.
> 
> Thanks in advance!
> Reza
>

So I'm looking at deploying a device with a Li-Poly battery on board.  
The voltage of a fully charged battery should be 4.2V, and will drop 
over time.  My application calls for a 3.3V source, and I was looking at 
using a LDO voltage regulator which has a *fault line to indicate when 
the voltage out is not correct (i.e. below 3.3v).  At this point, I 
would like to shut down the device, but I'm not sure how to do it.  If 
the device shuts down, I expect the voltage to rise above 3.3v, the 
device will power on again, the voltage will drop, it will shut down 
again.... et cetera... and just oscillate using up more battery and 
possibly permanently damaging it. 

This would seem like a common problem.  Has anyone else run into it -- 
and if so -- what solutions are available?  I can shut down a lot of the 
peripherals on the board, but there will be a number of components that 
I can't shut off and I don't want to run into the situation where the 
battery is bled dry.

Thanks in advance!
Reza

Disable all interrupts and put it to sleep?

Cat
----- Original Message ----- 

From: "Reza Naima" <reza@reza.net>
To: <AVR-Chat@yahoogroups.com>
Sent: Tuesday, July 24, 2007 4:06 AM
Subject: [AVR-Chat] [ot] Li-Poly regulation


> So I'm looking at deploying a device with a Li-Poly battery on board.  
> The voltage of a fully charged battery should be 4.2V, and will drop 
> over time.  My application calls for a 3.3V source, and I was looking at 
> using a LDO voltage regulator which has a *fault line to indicate when 
> the voltage out is not correct (i.e. below 3.3v).  At this point, I 
> would like to shut down the device, but I'm not sure how to do it.  If 
> the device shuts down, I expect the voltage to rise above 3.3v, the 
> device will power on again, the voltage will drop, it will shut down 
> again.... et cetera... and just oscillate using up more battery and 
> possibly permanently damaging it. 
> 
> This would seem like a common problem.  Has anyone else run into it -- 
> and if so -- what solutions are available?  I can shut down a lot of the 
> peripherals on the board, but there will be a number of components that 
> I can't shut off and I don't want to run into the situation where the 
> battery is bled dry.
> 
> Thanks in advance!
> Reza
> 
> 
> 
> Yahoo! Groups Links
> 
> 
> 
>

> ... there will be a number of components that I can't shut off and I 
don't want to run into the situation where the battery is bled dry.

If you can't allow a depleted battery (like LiIon and LiPos) you _must_ 
remove the load.  There exist LDO regulators that provide integrated 
power distribution switches; look at some USB power solutions like a 
TPS2148.  That part does not offer /Fail but you can, presumably, read 
the battery voltage with a resistive divider to an ADC input and make 
your own decision about when to shut down.  You could also, of course, 
use full battery management ICs, like most LiIon packs use.

You can also turn everything off with a simple suicide switch, a  MOSFET 
in series with the battery that's latched on by a processor control 
signal; remove the latching signal and the machine will stop - and stay 
that way since the battery is now disconnected.  You'll need a way to 
re-latch the switch to get going again, perhaps a pushbutton Start 
switch; I've heard described a way to do that with a DC power jack that 
will restart the processor as soon as a charger is attached, by using 
the sleeve shunt (the third jack pin).


Tom