It’s used together with the cell capacity to determine the maximum charge or discharge current. The C rating of a LiPo cell is a measure of how fast a cell can safely be charged or discharged. At this point the BQ2423 switches to constant voltage charging until the current drops to I END. This continues until the end-of-charge voltage V END is reached. Once V LOW is reached the charge proper begins and the current increase to I CHG. If the cell voltage is below V LOW a low constant charging current is provided in the pre-charge phase. This graph shows the voltage (red) and current (blue) curves for the various charging phases. Figure 1 shows the one-cell application schematic from the data sheet.įIGURE 2. This supports one or two LiPo cells and charge currents up to 2A. A good example is the TI BQ24123 switched-mode LiPo charger. Fortunately, there are a plethora of dedicated LiPo charger ICs out there that will manage the details for you. If you want to design in a LiPo cell or two and associated charger, you’ll need to take all this into account. If you have multiple cells in series, you may need to balance the voltage between them on a regular (or continuous basis) to maximize battery life. If you discharge one below 2.7V you can permanently damage the cell. If you overcharge a LiPo cell above 4.2V, or at too high a current, the electrolyte can vaporize, and the battery can expand and potentially rupture. They are however a bit fussy when it comes to how they must be charged and discharged, or they can be damaged or even catch fire. As a battery technology, they have lots of advantages over other rechargeable battery chemistries including high energy density, a relatively flat voltage profile over their discharge range, low self-discharge, and high discharge currents. Lithium Polymer (LiPo) batteries are pretty much ubiquitous these days, especially in consumer electronics.
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