The device I am building can be powered by USB or 3xAAA batteries. While connected to the USB, the device will charge the batteries. But before charging the batteries, the device needs to make sure the batteries are rechargeable.
I've made a circuit using BQ2002 to charge the batteries. If the batteries are not rechargeable, this circuit should not attempt to charge the battery (set charge control on BQ2002 to low).
How can I make sure my circuit doesn't try to charge every connected battery?
Is there a IC that has this functionality?
Best Answer
The Maxim (was Dallas Semi) DS2711 and DS2712 NiMh chargers include functionality to detect primary (i.e. non-rechargeable) cells. They do this by measuring the internal impedance of the cells, and using that to differentiate between NiMh (lower impedance) and primary cells (higher impedance), as explained in this Maxim Application Note 3388.
The abstract from that AppNote says:
Unfortunately for your application, as you can see in that abstract, those Maxim devices are designed for recharging 1 or 2 cells - not your 3-cell design. Options include modifying your design to use only 1 or 2 cells and, if your design needs it, adding a boost converter to match the higher output voltage of 3 cells (assuming the existing 3-cell design has them connected in series) or trying to incorporate the same impedance measurement technique as they use, into your own design (but perhaps check for any patents that might apply, if you do that).