Talking about the charging method of lithium battery

Talking about the charging method of lithium battery :

The charging method of lithium batteries varies with the number of cells, cell configuration, and power type. At present, lithium battery charging mainly includes three methods: linear, Buck (buck) switch and SEPIC (boost and buck switch). The specific operations are as follows:

1. Linear charging method of lithium battery

When the input voltage of the charger is greater than the open circuit voltage of the fully charged cell plus enough margin, it is best to use a linear solution, especially when the 1.0C fast charging current is not greater than 1A.

For example: MP3 players usually have only one lithium battery, the capacity ranges from 700 to 1500mAh, and the open circuit voltage after full charge is 4.2V. The power supply of the MP3 player is usually an AC/DC adapter or a USB interface, and the output is ordinary 5V; at this time, the charger of the linear scheme is the simplest and most efficient scheme. Charger Application Example for Linear Solutions - Dual Input Li+ Charger and Smart Power Selector is a dual input USB/AC adapter linear charger with a built-in smart power selector for portable devices powered by rechargeable single-cell Li+ batteries. The charger integrates all the power switches needed to charge the battery and external power and switch the load, so no external MOSFETs are required: the MAX8677A is ideal for convenience.

Portable devices such as smartphones, PDAs, portable multimedia players, GPS navigation devices, digital cameras and camcorders When connected to external power, the Smart Power Selector allows the system to connect without a battery or a deeply discharged battery. Smart The power selector automatically switches the battery to the system load, uses the unused portion of the system input power to charge the battery, and takes advantage of limited USB and adapter input power. All required current sensing

Circuitry including integrated power switches is integrated on the chip. The DC input current limit is adjustable up to 2A, while both DC and USB inputs support 100mA, 500mA and USB suspend modes. The charging current can be adjusted up to 1.5A to support various battery capacitances. Additional features of the MAX8677A include thermal regulation, overvoltage protection, state-of-charge and fault detection, power-good monitoring, battery thermistor monitoring, and a charge timer. The MAX8677A is available in a space-saving thermally enhanced 4mmx4mm 24-pin TQFN package and is specified over the extended temperature range (-40 to +85°C)

2. Buck (buck) switch charging method of lithium battery

When the 1.0C charging current is greater than 1A, or the input voltage is much higher than the open-circuit voltage of the cell's full charge, the Buck or step-down solution is a better choice. For example, in a hard disk-based PMP, a single-cell lithium-ion battery is usually used, with an open circuit voltage of 4.2V when fully charged, and a capacity of 1200~2400mAh. Now the PMP is usually charged with a car kit, and its output voltage is between 9V and 16V. The relatively high voltage difference between the input voltage and the Li-ion battery voltage (z smaller by 4.8V) reduces the efficiency of the linear scheme. This inefficiency, combined with the 1C fast charge current greater than 1.2A, creates serious thermal problems. In order to avoid this situation, it is necessary to adopt the Buck scheme

3. SEPIC (step-up and step-down) switch charging method of lithium battery

In some devices using 3- or even 4-cell Li-Ion/Polymer batteries in series, the input voltage to the charger is not always greater than the battery voltage. For example, a notebook computer uses a 3-cell lithium-ion battery pack with an open circuit voltage of 12.6V (4.2V×3) when fully charged, and a capacity from 1800mAh to 3600mAh. Input power can be an AC/DC adapter with an output voltage of 16V, or a car kit with an output voltage between 9V and 16V. Obviously, neither the linear scheme nor the buck scheme can charge this battery pack. This adopts SEPIC scheme, can work when the output voltage is higher than the battery voltage, can also work when the output voltage is lower than the battery voltage.