Gas gauge IC & battery swap

[Dominique]

Hi,

I'm working on an handheld device project powered from a removable 3200mAh single-cell Li-ion battery and running Windows CE (maybe Linux in the future). The remaining battery charge should be reported accurately to the user. Normal operation includes charging over USB, however the user may swap different batteries - e.g. replacing a depleted battery by a fully charged one, using an external charger.

I'm looking at various li-ion gas gauges datasheets, and I don't understand how they would handle a battery replacement. They all seem to keep track of the charging status using non-volatile memory, so I guess they would start with a wrong estimation of the charge when a new battery is inserted.

Can somebody enlighten me on the subject ? Specific IC suggestions would also be of great help.

Thanks,
Dominique

[SeanB]

If using a battery pack put the management IC into the pack and connect it into the circuit via a multipole connector. That way you also have memory in the pack to store info about the pack, and most management IC' s allow you to charge the pack and have it balance the cells with pretty much no external control other than a preset set in the pack.

[ohmineer]

Actually there are gas gauges that are designed to be placed into the battery pack and others into the system. You can usually filter by this options in manufacturer's website (See Texas Instruments or Maxim Integrated).

In general, gas gauges that allow changing the battery pack (System side gas gauges) rely their estimations on open circuit voltages (relaxation) and dynamic behaviour of the pack (during charge and discharge). Data stored in ROM is used to improve accuracy when battery pack is connected.

For those reasons, the cell modelling stage when designing the system is very important if you want to be accurate.