Dear all,

I have a micro-controller based system powered using a Li-Lion battery packed rated at 7.4V, 4400mAH(2S2P - 2 cells in series and 2 circuits in parallel). The system output is 12V, provided through a boost circuit. The boost circuit is shut-down when the battery voltage reaches 6.8Volts.

However if the user does not charge the battery regularly, then through self-discharge the battery pack voltage falls below 4.8Volts, the PCM circuits inside the battery pack, stop any further discharge of the cells. Thus the output voltage from the pack is 0.0 V.

Now when the user tries to restart the system, he cannot since there is no power available to the micro-controller. So the battery cannot now be charged and so the system cannot be turned on.

I thought of one option which is to provide some additional circuit using a single-cell to power on the micro-controller. Once the charging starts the battery pack should be able to take over. BUT that is not a practical solution. I do not have the luxury of increasing the system cost by adding another battery.

Do any of you have any experiences which you can share? Do you have any thoughts on what I could do to remedy this problem?

Feel free to ask any questions..

Regards

 

Why does the microcontroller need to be powered to charge the battery?

When you plug in the system to charge, the power should directly go to the lipo charging IC, and that should charge the battery.

 

I've designed many handheld systems based on Li-Ion batteries, exactly as you describe. I always made the charger stand-alone (menaing that it does not require the micro-controller to work). This ensures that a dead battery can be charged enough to start-up the system.

 

Modify your system so that it shuts down when there is still a little charge left in the battery. Only allow the processor to be started under low charge conditions.

 

Why does the microcontroller need to be powered to charge the battery?

Actually it may not, however it is the way the system was designed. However from what you said, gave me an idea to take care of my problem.

I can connect the charging voltage directly to power the micro-controller, which should wake up and start the charging process.

Thanks again for hearing out my problem!

 

I've designed many handheld systems based on Li-Ion batteries, exactly as you describe. I always made the charger stand-alone (menaing that it does not require the micro-controller to work). This ensures that a dead battery can be charged enough to start-up the system.

I think that is a very good suggestion. Maybe from now on that should be my strategy as well.

From my current experience, even though I designed a cut-off for the system when the battery falls below a certain limit, BUT that also does not prevent this situation from arising. The user forgets to charge the system, and the self discharge of the battery takes it below the 2.4V threshold.

I think one solution could be to power the micro-controller directly from the charging supply which will wake it up. Then the charging process can start.

Option 2: Design the charging circuit purely in hardware, without the micro-controller having any role in the charging process.

Thanks again for all the suggestions.