Li-Ion (Lithium) Battery - Charger and protection ICs ???

Discussion in 'The Projects Forum' started by esm., Mar 3, 2012.

  1. esm.

    Thread Starter Member

    Jan 20, 2012

    I am designing a power supply where I will also need to use a backup battery.
    The choosen battery type was a Li-Ion (Lithium) type, which has a nominal cell voltage of 3.7V .
    I have little experience with battery chargers and protection circuits (using dedicated ICs).

    --> I searching for dedicated charger ICs and I think MCP73812 from Microchip is a good choice to do the automatic charge control.
    Using a MCP73812 I am able to ENABLE/DISABLE and ADJUST the charge current through an external bias resistor.

    --> I was also searching for a Li-Ion battery protection IC, to "disconnect" the BATT from the circuit in situations of under-

    voltage (over-discharge) and over-voltage (over-charge). I found this IC model on Digikey: S-8241ABKMC-GBKT2G. This IC (S-8241ABKMC-GBKT2G) controls two MOSFETs who are connected between the Li-Ion battery and the circuit's power supply.

    The S-8241ABKMC-GBKT2G IC works similar to that:

    1) It is powered from the Li-Ion battery and its current consumption is very very low, just some microamperes or less, when in power-down mode.

    2) When the BATT voltage goes below 2.5V, it "opens" the MOSFET switch, preventing the BAT to continue supplying current to the circuit. It "closes" the MOSFET switch again only when the BATT voltage goes above 2.9V. This is a good idea, using a small voltage hysteresis between OPENING and CLOSING the MOSFET switch, preventing oscilations.

    3) When the BATT is in charge process and its voltage reaches 4.325V, the S-8241ABKMC-GBKT2G "opens" the MOSFET switch, preventing the BAT to continue charging and being "over-charged". S-8241ABKMC-GBKT2G "closes" the MOSFET switch again only when the BAT voltage goes below 4.075V. This is a good idea, using a small voltage hysteresis beetwenn OPENING and CLOSING the MOSFET switch, preventing oscilations.

    4) S-8241ABKMC-GBKT2G has two digital outputs to control two mosfets, one for under-volge and another for over-voltage cases. So using just the under-voltage output, we could use this same IC to protect battery circuits who uses NiMh (more than one cell in series) backup batteries.

    - MCP73812 -->> Simple, Miniature Single-Cell, Fully Integrated Li-Ion / Li-Polymer Charge Management Controller




    I don't want to use Lead-Acid, NiCd or NiMh battery anymore. Just Li-Ion from now on hehehe.

  2. #12


    Nov 30, 2010
    Darn...I had one of those charger chips on my desktop a couple of days ago. This site is littered with fast switching single cell chargers and OVP/UVP protection, but I haven't seen better than what you've done for yourself.
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
    National Semiconductor made an Li protection IC some years back, I was the one who defined it but I didn't stay on the team that released it. We called it "LI-PRO" in house, don't know what the part number ended up being.

    You should also check Maxim, they make a ton of similar products.

    Motorola made the first Li protection ICs for Sony, they may still offer one.
  4. dmarciano


    Oct 10, 2007
    I have a similar requirement where my device is going to run off of 2 Li-Ion batteries. When not connected to an external source the circuit should run off the batteries, but when plugged in the batteries should charge while also allowing the device to be used.

    This is something that I haven't done before so I've been doing research for the past few hours trying to figure out how to go about this, unfortunately I wasn't able to find any circuit that showed this. Everything I came across was either a charging circuit or a circuit running off of Li-Ion batteries, not both. So I came across this IC MCP73842 (Datasheet since it will allow me to charge two-cells.

    However how can I hook up the rest of my system to it? I can't just connect the system across the terminals of the battery can I? I doubt it can be done because the maximum supply current of the MCP73842 is +/- 4mA an my circuit is going to be drawing more then that. My circuit is going to contain an PIC18F28K22 (-0.3 to +6.5V), 24AA08 (1.7 to 5.5V), and MCP2200 (3.0 to 5.5V) which will be run off of two separate voltage regulators (one for PIC, and one for the other two).

    If I'm going about this the wrong way I'm open to suggestions. I simple need a design which will supply my circuit from a battery when no external power is applied AND charge the battery and run the circuit when external power is supplied. I look for to suggestions and thanks in advance for any help with this.