A Lithium Battery Charger with Load Sharing

[chota.sanjiv]

Hi Guys,

I was referring the following circuit for battery charger with load sharing ie. the circuit will get powered via main power and when its not there it will switch to battery immediately, in the circuit I cannot understand the R2 pull down ,won't it cause extra power consumption for my circuit. ?

http://blog.zakkemble.co.uk/wp-content/uploads/2013/05/MCP73831_loadshare.png

regards,
Sanjeev

[ConKbot]

Without r2, what happens when the charger is removed? The voltage on the VDD net will be floating at a point where the diode leakage and current used by the charger ic are equal. The mosfet may not be turned on fully or at all, adding a diode drop between the battery and the load. With the pulldown, VDD goes to ground, the mosfet his turned on fully, and the load gets full battery voltage.

[Signal32]

As ConKbot mentioned, R2 is required so that the circuit will function correctly. And yes, you are correct, it will add extra load to your circuit, though a very small one (0.05mA).