Problems with Max1811 Li-Ion Charger IC

Hi,

I recently build a Li-Ion-Charger around the Maxim Max1811 Li-Ion Charger IC (datasheet: http://datasheets.maxim-ic.com/en/ds/MAX1811.pdf). The Eagle Files of my board can be found here:

http://rapidshare.com/files/355044304/Li-Ionen-Lader.zip.html

The 3 Inputs to the Max1811 are determined by simple 3-header-jumpers with 5V and GND at the sides and a trace to the input in the middle, so I can jumper the inputs to VIN (5V) or GND.
The headers on the right side of the board connect to the battery terminals, the unconnected 15-pin-header on the left side has a bit of Styrofoam on it to press the terminals against the charging headers.
The 5V and GND rails are momentarily taken from an Arduino Board, which is powered by a 9V 800mA Wall Adapter.
The LED is an orange one (i think it has a min. voltage of 1.8V or something) and is hooked up to the CHG-pin via a 330Ohm-resistor to VIN.

The problem is with this LED hooked up to the CHG-pin. When the charger is in 100mA-Mode, it slowly charges the battery and the LED lights up (the battery hasn’t reached 4.1V yet). That seems right.

However when I jumper the charger to charge with 500mA, the LED only lights up for a short time (half a second max). Looks like some kind of emergency cutoff of the IC to me, but the IC is not really warm (not the 125°C mentioned in the datasheet), you can comfortably touch it with a finger. I only felt the warmth when touching with my lips (with the board off power). There also seems to be no charging happening in 500mA-mode.

Does anyone have an idea why the charger doesn’t charge with 500mA?

Regards, Otacon2k

Hi,

Check the answers here: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1252925145/11. The power regulator could have problems supplying 500mA over time. That may be the issue.

Joachim

Thank you for the link. I had already read it before, though now I think I’m gonna try to just hook the Max1811 directly to a wallwart to bypass the voltage regulator problem or use an extra LM317, which I have lying around (who doesn’t ;)) and which, acoording to the datasheet, can handle a maximum output current of more than 1A (under my circumstances at least).

Nevertheless, from the Arduino’s Voltage regulator’s datasheet (http://pdf1.alldatasheet.com/datasheet-pdf/view/12048/ONSEMI/MC33269D-5.0.html) it seems like the regulator could possibly deliver 500mA (or more). Depends on the IC package…
and as I’m at work an don’t have access to eagle I can’t look into the reference files to see which of the ICs above the powerjack on my Duemilanove is the regulator :slight_smile:

Well, I’m gonna try further when I’m back home and keep you updated.

Have a nice day, Otacon2k

Update:

I tried powering the Max1811 with a little LM317T-circuit. The voltage regulator has got a heatsink and drops 9V to 4.4V, so the Max1811 runs on minimal voltage (4.35V) to minimize heat, which results in a downregulated charging current. The 4.6V voltage drop @ 500mA in the voltage regulator are near the given maximal values when not using a heatsink (if i calculated correctly), so with a heatsink added it should be ok.
The problem remains. As soon as I power up the charging circuit the orange LED flashes for a very short moment and then stops shining. So I assume it has nothing to do with the voltage supply.
Any other ideas someone? Could it be the caps’ values? This flashing of the LED somehow reminds me of a discharging capacitor…

Ideas welcome :wink:

Otacon2k