The application of the battery technology of portable electronic devices is the basis for choosing lithium-ion batteries and lithium polymer batteries and their chargers. The correct choice must also depend on the specific requirements of the portable electronic devices.

　　1. Battery charging algorithms for trickle charging, fast charging and stable charging

　　According to the energy requirements of the final application, a battery pack may contain up to 4 lithium ion or lithium polymer battery cells, and its configuration can be varied, and it also has a mainstream power adapter: direct adapter, USB interface or car charging Device.

　　*Trick current charging. It is used to charge deeply discharged batteries. When the cell voltage is lower than about 2.8V, a constant 0.1C current is used to charge it.

　　*Fast charging. When the cell voltage exceeds the threshold of trickle charging, increase the charging current for fast charging. The fast charge current should be lower than 1.0C.

　　* Stable voltage. During the fast charging process, once the cell voltage reaches 4.2V, the voltage stabilization phase begins. At this time, the charging can be interrupted by the minimum charging current or the timer or the combination of the two. When the minimum current is lower than about 0.07C, the charging can be interrupted. The timer relies on a preset timer to trigger an interrupt.

　　Advanced battery chargers usually come with additional safety features. For example, if the cell temperature exceeds a given window, which is usually 0°C--45°C, charging will be suspended. Except for some very low-end devices, the current lithium-ion/lithium-polymer battery charging solutions on the market are integrated or have external components to charge according to the charging characteristics. This is not only to achieve better charging results, It is also for safety.

　　2, Li-ion/polymer battery charging scheme

　　Li-ion/polymer battery charging schemes are different for different numbers of cells, cell configuration, and power source types. There are currently three main charging schemes: linear, Buck (buck) switch and SEPIC (boost and buck) switch.

　　2.1 Linear scheme

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

　　MAX8677A can work under independent USB and AC adapter power input or under either input of two inputs. When connected to an external power source, the smart power selector allows the system to be disconnected from a battery or can be connected to a deeply discharged battery.

　　2.2Buck (buck) switch scheme

　　When the 1.0C charging current is greater than 1A, or the input voltage is much higher than the fully charged open circuit voltage of the cell, Buck or a step-down solution is a better choice. For example, in a hard disk-based PMP, a single-cell lithium-ion battery is usually used, the open circuit voltage is 4.2V when fully charged, and the capacity ranges from 1200 to 2400mAh. Now PMP is usually charged with a car kit, and its output voltage is between 9V and 16V. The relatively high voltage difference (minimum 4.8V) between the input voltage and the battery voltage will reduce the efficiency of the linear scheme. This low efficiency, coupled with a 1C fast charging current greater than 1.2A, will cause serious heat dissipation problems. In order to avoid this situation, it is necessary to adopt the Buck scheme. Figure 3 is a schematic diagram of a lithium-ion/polymer battery Buck charger scheme. The basic structure is exactly the same as the Buck (buck) switching voltage regulator.

　　2.3SEPIC (boost and buck) switching scheme

　　In some devices that use 3 or 4 lithium-ion/polymer cells in series, the input voltage of the charger is not always greater than the battery voltage. For example, a laptop computer uses a 3-cell lithium-ion battery pack with a fully charged open circuit voltage of 12.6V (4.2Vx3) and a capacity from 1800mAh to 3600mAh. The input power supply is either an AC/DC adapter with an output voltage of 16V or a car kit with an output voltage between 9V and 16V. Obviously, neither linear nor Buck solutions can charge this battery pack. This requires the use of the SEPIC solution, which can work when the output voltage is higher than the battery voltage, and can also work when the output voltage is lower than the battery.

　　3, power detection algorithm

　　Many portable products use voltage measurements to estimate the remaining battery power, but the relationship between battery voltage and remaining power will change with the discharge rate, temperature, and battery aging. This method has the highest error rate. Up to 50%.

　　3.1 One of the application examples of the power detection algorithm, a fully functional single/dual battery portable application battery pack design

　　*The principle of power detection. A better power meter must at least have battery voltage, battery temperature and current, measurement methods; a microprocessor 9a; and a set of proven power detection algorithms. The bq2650x and bq27x00 are fully functional fuel gauges with an analog-to-digital converter (ADC) for measuring voltage and temperature and an analog-to-digital converter for measuring current and charging sensing.

　　*Battery pack circuit description. Figure 4(a) is a typical battery pack application circuit that can choose to use an IC with identification function. Depending on the fuel gauge IC used, the battery pack needs at least three to four external terminals. The VCC and BAT pins will be connected to the battery voltage in order to supply power to C and measure the battery voltage.

　　3.2 The second example of the application of the power detection algorithm, which can be applied to a variety of new ICs for general-purpose fuel meters.

　　Many manufacturers nowadays can provide a wide range of fuel gauge ICs, from which users can select suitable functional devices to optimize the cost-effectiveness of their products. Utilizing the battery parameters measured by the fuel gauge, this separate architecture allows users to customize the fuel gauge algorithm in the host. This saves the cost of the embedded processor in the battery pack. At this time, take the DS2762 chip named as an example of Dallase Semiconductor Company for typical analysis. A new type of separate fuel gauge IC, the structure of which is shown in Figure 5(a).

　　4 Conclusion

　　The application of the battery technology of portable electronic devices is the basis for choosing lithium-ion batteries and lithium polymer batteries and their chargers. The correct choice must also depend on the specific requirements of the portable electronic devices.