Simplified Lithium-Ion (Li+) Battery-Charger Testing - Reference Design - Maxim

Because the charging process for Li+ batteries can take an hour or longer, testing a Li+ battery charger using its natural load (i.e., a battery) is time consuming and inconvenient. This application note presents a simple circuit for simulating the behavior of a Li+ battery, thus providing a more convenient method for testing Li+ battery chargers than using real batteries. A similar version of this article was featured in Maxim's Engineering Journal, vol. 64 (PDF, 1.99MB). Introduction Lithium-ion (Li+) batteries are more delicate than other battery chemistries and have little tolerance for abuse. Consequently, Li+ battery chargers are complex circuits, requiring highly accurate current and voltage settings. If these accuracy requirements are not met, the charger may fail to completely charge the battery, severely reduce battery life, or otherwise degrade battery performance. Given the demands imposed on Li+ chargers, it is critical that charger designs be tested thoroughly and stepped through their entire operating range. However, testing a Li+ charger with its natural load (i.e., a Li+ battery) can be time consuming and impractical in laboratory and production environments. To simplify the process, this article presents a battery-emulation circuit for accelerated, realistic testing of Li+ battery chargers without actual batteries. CC-CV Charging The Li+ battery-charging process requires medium-accuracy constant-current (CC) charging in a first phase, transitioning to high-accuracy constant-voltage (CV) charging in a second phase. Figure 1 illustrates the V-I characteristics of a modern CC-CV integrated circuit (the MAX1737) used for a Li+ battery charger. This type of IC is at the heart of all Li+ battery chargers in consumer products. The CC (between 2.6V and 4.2V battery voltage) and the CV (4.2V) regions are clearly shown.