That's probably because the A/D portion of the code can't run at 1.6V, so only the IRQ part is actually running (at 1.8uA) and that will probably last quite a long time. -Mark
-----Original Message----- From: Kelly Murray [mailto:k...@netnimble.com] Sent: Tuesday, May 04, 2004 5:04 PM To: mspgcc-users@lists.sourceforge.net Subject: Re: [Mspgcc-users] sleep mode power consumption Thanks for the calculations. The Cap I'm using is a "1F SuperCap" with .22F @ 5v, i.e. 220000uF @5v It's an old surplus one, it might just leak badly, but the funny thing is stablizes at 1.66v. Stokes, Mark wrote: >A/D conversions take quite a bit of power (.65 to 1.6mA for the converter and >.5 to .8mA >for Vref for the F44x series per conversion for the duration of the conversion >{according to SLAS344A}). Perhaps you need to add this to the power >requirements when >calculating how long the MSP should take. Sure, in shutdown, it takes 1.8uA >or so, but >the A/D would be "on top" of that. Also, A/D conversions can be made to >happen in the >background, so that's a consideration also. >If it were me, I'd suggest a supercap of something like 1F or something. That >should >keep the MSP430 on for quite a long time. >Simple calculation (not necessarily complete): >.65 + .5 = 1.1mA per conversion during conversion. Let's just say the >conversion takes >300us (completely made up). So, that gives us: >1.1mA * .0003 = 3.3x10-7 A-Seconds. Or, 5.5x10-9 A-Minutes Or: 9.167x10-11 >A-H. >If we take that a capacitor discharges according to the formula: > >Vt=Vo(e^(-t/RC)) >Where >Vt=voltage at time t >Vo=Voltage at time 0 >t=time in seconds >And R and C in ohms and farads >AND we characterize the above A-s values to an equivalent parallel RC circuit >(major >generalizations), then, we can calculate for t (using a 10M ohm resistor which >gives >roughly 3.3x10-7A-s at 3.3v). >Using Excel, and calculating to V=1.8v (spec of MSP), then I get roughly 6s >for a 1uF >cap. Not very long at all. And of course this is assuming a perfect cap w/ >no ESR, >etc. >Of course, this also doesn't take into account that the voltage is decaying, >and so >would the current in the RC circuit (I'm not sure what would happen in the >430), so that >would have an impact also. >Hope this helps. >-Mark > > > >-----Original Message----- >From: Kelly Murray [mailto:k...@netnimble.com] >Sent: Tuesday, May 04, 2004 12:55 PM >To: mspgcc-users@lists.sourceforge.net >Subject: [Mspgcc-users] sleep mode power consumption > >Hello, >I've got a system where I use the MSP430 to turn off the power if the >system is >idle for some time, and then wake it back up if there is any user input. > >Of course, this is not possible, if the power is off, the MSP430 can't run! >But I use a .22F 3v capacitor that is charged up while power is on, and >then runs >the MSP when the power is off. > > The strange thing is that when I monitor the >voltage after power-down, the cap is loosing voltage rather quickly, >about .01 v per second, >until it hits 1.66V and then stays there. This should be less than the >voltage needed to run the MSP? >I think the specs say 1.8v. However, it does still seem to be running, >because it is still monitoring >the input and turns the power back on. > >My guess is that perhaps this behavior is "just lucky", that at 1.66v >the MSP is barely operating. >Alternatively, I suspect that because the 1.66v is also used as a logic >pin to shutdown the power, > it may be dipping below an "off" value for a tiny fraction of time, >just enough to give the cap >some juice enough to run the MSP, but not detectable by my voltmeter. > >Anyone have any ideas or suggestions? Isn't 1.66v too low to operate >the MSP4301232 ? >Any why is cap dropping so quickly from 3v, in shutdown mode, it should >draw very little power, >just enough to wake up every second and do a A/D reading. > >thanks for any input, >Kelly Murray > > > > >------------------------------------------------------- >This SF.Net email is sponsored by: Oracle 10g >Get certified on the hottest thing ever to hit the market... Oracle 10g. >Take an Oracle 10g class now, and we'll give you the exam FREE. >http://ads.osdn.com/?ad_id=3149&alloc_id=8166&op=click >_______________________________________________ >Mspgcc-users mailing list >Mspgcc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/mspgcc-users > > >------------------------------------------------------- >This SF.Net email is sponsored by: Oracle 10g >Get certified on the hottest thing ever to hit the market... Oracle 10g. >Take an Oracle 10g class now, and we'll give you the exam FREE. >http://ads.osdn.com/?ad_id149&alloc_id66&op=click >_______________________________________________ >Mspgcc-users mailing list >Mspgcc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/mspgcc-users > > > > ------------------------------------------------------- This SF.Net email is sponsored by: Oracle 10g Get certified on the hottest thing ever to hit the market... Oracle 10g. Take an Oracle 10g class now, and we'll give you the exam FREE. http://ads.osdn.com/?ad_id=3149&alloc_id=8166&op=click _______________________________________________ Mspgcc-users mailing list Mspgcc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mspgcc-users
