Electrical – Remove over-current protection of battery protection circuit

batteriesbattery-chargingcell-batterylipo

I have a hardware that is powered by a standard polymer battery (http://www.ebay.com/itm/3-7V-Polymer-Rechargeable-Battery-2000mAh-PCM-103450-for-GPS-ipod-Tablet-PC-MP3-/262605237924).

The hardware draws a lot of current, more than 3A, perhaps up to 5A. This triggers the overcurrent protection of this battery. The protection circuitry includes two SOT23-6L (http://www.phaselink.com/QA/SOT23-6L.pdf) ICs:

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As replied on this question (Over current protection for a 1-cell battery), the overcurrent protection is probably set up for 3A (25mohm ron of mosfets).

I would like to "decrease" the overcurrent protection up to 5A without losing the overdischarge protection. My options are:

  • either replacing the dual mosfets. But I can't find any SOT23-6L with Ron=10mohm. 25mohm seems to be the minimum.

  • or shorten M1 to disable the overcurrent protection. But I think it will disable the overdischarge detection voltage.

How can I fix my problem?

Best Answer

The circuit looks for voltage drop across two power mosfets. It looks like the sensing circuit is between CS pin and GND pin.

Instead of looking for MOSFETs with lower Rdon, you can make a divider, splitting the R2 in two resistors, and connect the CS pin to the middle of the divider. The voltage between CS and GND will drop, IC will think that the current is small, and will trigger the overcurrent threshold at higher drop-through voltage.

Just try to connect another 1k resistor between CS and GND, and see if the cell will deliver more current before cut-off.