Battery charging algorithm for trickle charging, fast charging and stable charging
Depending on the energy requirements of the final application, a battery pack may contain up to four lithium-ion or lithium-polymer battery cells in a variety of configurations, with a mainstream power adapter: direct adapter, USB interface or car charging Device. These battery packs have the same charging characteristics, regardless of the number of cells, the configuration of the cells, or the type of power adapter. So their charging algorithms are the same. The best charging algorithms for lithium-ion and lithium-polymer batteries can be divided into three phases: trickle charging, fast charging, and stable charging.
* Trickle charging. Used to charge deep-discharged cells. When the cell voltage is below about 2.8V, it is charged with a constant current of 0.1C.
* Fast charging. When the battery voltage exceeds the threshold of trickle charging, increase the charging current for fast charging. The fast charging current should be below 1.0C.
* Stable voltage. During the fast charging process, once the cell voltage reaches 4.2V, the steady voltage phase begins. At this time, the charging can be interrupted by a minimum charging current or a timer or a combination of the two. When the minimum current is lower than about 0.07 C, the charging can be interrupted. The timer relies on a preset timer to trigger an interrupt.
Advanced battery chargers usually come with additional security features. For example, if the cell temperature exceeds a given window, typically 0°C--45°C, charging will be suspended.
In addition to some very low-end devices, the current Li-Ion/Li-Polymer battery charging solutions are integrated or have external components to charge according to the charging characteristics, not only for better charging. It is also for safety.
* Lithium ion / polymer battery charging application example - dual input 1.2A lithium battery charger LTC4097
The LTC4097 can be used to charge a single-cell Li-Ion/Polymer battery with an AC adapter or USB power supply. Figure 1 is a schematic diagram of the dual-input 1.2A lithium battery charger LTC4097. It uses a constant current / constant voltage algorithm to charge, programmable charging current up to 1.2A when charging from the AC adapter power supply, and up to 1A with USB power supply, while automatically Detect if there is a voltage at each input. The device also provides USB current limit. Applications include PDAs, MP3 players, digital cameras, lightweight portable medical and test equipment, and large color screen cellular phones. Its performance features: no need for external microcontroller to terminate charging; input power supply automatic detection and selection; programmable charging current through the resistor input from the AC adapter input up to 1.2A; programmable USB charging current through the resistor up to 1A; 100% or 20 %USB charging current setting; input power supply output and NTC bias (VNTC) pin with 120mA drive capability; NTC thermistor input (NTC) pin for temperature qualified charging; preset battery floating voltage with ±0.6% Accuracy; thermal regulation maximizes charge rate without overheating The LTC4097 can be used to charge a single-cell Li-Ion/Polymer battery with an AC adapter or USB power supply. It uses a constant current/constant voltage algorithm to charge, programmable charge current up to 1.2A from the AC adapter power supply, and up to 1A with USB power, while automatically detecting the presence of voltage at each input. The device also provides USB current limit. Applications include PDAs, MP3 players, digital cameras, lightweight portable medical and test equipment, and large color screen cellular phones.