Hottest battery and charging management selection

2022-08-16
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Battery and charging management: selection and trade-off factors

Introduction

portable electronic device designers can choose a variety of chemical technologies, charger topologies, and charging management solutions. Choosing the most appropriate solution should be a very simple task, but in most cases, the process is quite complex. Designers need to find the best balance between performance, cost, overall dimensions and other key requirements. This paper will provide some guidance and help for designers and system engineers to make the selection easier

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all system designers using rechargeable batteries need to know some basic design techniques to ensure that the following three key requirements are met:

1. Battery safety: there is no doubt that the safety of end users is the top priority in all system design. Most Li ion batteries and Li pol batteries contain protective electronic circuits. However, there are still some key factors that need to be considered in system design. This includes but is not limited to ensuring that during the final stage of lithium-ion battery charging? 1% voltage stabilization tolerance, safe treatment of pretreatment mode of deep discharge battery, safety timer and battery temperature monitoring

2. Battery capacity: all battery charging solutions should ensure that the battery capacity can be fully charged at every time and every charging cycle. Premature termination of charging will shorten the battery running time, which is not expected by today's high-power portable devices

3. Battery life: following the recommended charging algorithm is an important step to ensure that end users can achieve the maximum charging cycle of each battery pack. Using battery temperature and voltage to limit each charge, pretreat the deep discharge battery and avoid too late or abnormal charging termination are necessary steps to maximize the service life of the battery. Table 1: charging control summary

selection of battery chemistry technology

now system designers can choose from a variety of battery chemistry technologies. Designers usually choose battery chemistry technology according to the following standards, including:

* energy density

* specifications and overall dimensions

* cost

* use mode and service life

in recent years, although the trend of using lithium-ion batteries and lithium polymer batteries has increased, Ni battery chemistry technology is still a good option for many consumer applications

no matter which battery chemistry technology is selected, it is essential to follow the correct charging management technology of each battery chemistry technology. These technologies will ensure that the battery can be charged to its maximum capacity every time and every charging cycle, without reducing safety or shortening the service life of the battery

nicd/NIMH

nickel cadmium (NiCd) batteries and nickel hydrogen (NIMH) batteries must be inspected and adjusted before a charging cycle and as soon as possible before starting rapid charging. If the battery voltage or temperature exceeds the allowable limit, rapid charging is not allowed. For safety reasons, the charging of all "hot" batteries (generally higher than 45 ° C) will be temporarily terminated until the batteries are cooled to the normal operating temperature range. To handle a "cold" battery (generally lower than 10 ° C) or an over discharged battery (each battery is usually lower than 1V), a mild trickle current needs to be applied

when the battery temperature and voltage are correct, the fast charging starts. NiMH batteries are usually charged with a constant current of 1C or less. Some NiCd batteries can be charged at a rate of up to 4C. Adopt appropriate charging termination to avoid harmful overcharge

for nickel based rechargeable batteries that can resist oil and corrosion, rapid charging termination is based on voltage or temperature. As shown in Figure 1, the typical voltage termination method is peak voltage detection. At peak value, that is, the voltage of each battery is within the range of 0 ~ -4mv, and the rapid charging is terminated. The fast charge termination method based on temperature is to observe the temperature rise rate of the battery △ t/△ t to detect full charge. The typical △ t/△ t rate is 1 ℃/minute

Figure 1: charging curve of nickel battery chemistry technology

Lithium Ion/lithium polymer battery

similar to NiCd battery and NiMH battery, check and adjust lithium-ion battery as much as possible before rapid charging. The verification and treatment methods are similar to those used above

as shown in Figure 2, after verification and pretreatment, charge the lithium-ion battery with a current of 1C or less until the battery reaches its charging voltage limit. This charging phase usually replenishes up to 70% of the battery capacity. Then charge the battery with a constant voltage, usually 4.2V. In order to ensure safety and battery capacity, the charging pressure must be stabilized at least? 1%。 During this charging period, the charging current drawn by the battery gradually decreases. In terms of 1C charging rate, once the current level drops below% of the initial charging current, the charging will usually terminate

Figure 2: lithium ion battery chemical technology charging curve

comparison between switching mode and linear charging topology

traditionally, handheld devices use linear charging topology. This method has many advantages: low implementation cost, simple design and noiseless operation without high frequency switch. However, linear topology will increase the power consumption of the system, especially when the charging rate increases due to higher battery capacity. If designers cannot manage the heat dissipation of the design, this will become a major disadvantage

when the PC USB port is used as the power supply, there will be some other disadvantages. Today, many portable designs have USB charging options, and can provide a charging rate of up to 500mA. In terms of linear solutions, due to its low efficiency, the amount of "power" that can be transferred from PC USB is greatly reduced, resulting in a long charging time

this is why switching mode topology is useful. The main advantage of switching mode topology is the improvement of efficiency. Unlike linear regulators, power switches (or multiple switches) operate in saturated regions, which greatly reduces overall losses. The power loss in step-down converter mainly includes switching loss (in power switch) and DC loss in filter inductance. According to the different design parameters, it is not surprising that the efficiency is much higher than 95% in these applications

when people hear the term switching mode, most people will think of large IC, large powerfet and super large inductor! In fact, although this is true for applications that handle tens of amperes of current, the situation is different for next-generation solutions for handheld devices. The new generation of single lithium ion switching mode charger adopts the highest level of chip integration, with a frequency higher than 1MHz to minimize the inductance size. Figure 1 illustrates such solutions that are already on the market today. The size of the silicon chip is less than 4 mm2, and it integrates high side and low side powerfet. Due to the 3MHz switching frequency, the solution requires a small 1uh inductor, whose overall dimension is only 2mm x 2.5mm x 1.2mm (wxlxh)

charger selection

battery charger tool makes the process of selecting the right charger easier for designers. Figure 3 is an example of a tool provided on the Ti station

references

* for more information about the battery charging selection tool to help the material testing machine upgrade to meet the requirements of national standards, please visit:

* for more details about ti's solution and other power solutions, please visit:

introduction to the author

masoud Beheshti is currently the director of Ti battery charging management. He has been engaged in design, product definition, strategic marketing and business management in the field of power supply and battery management for more than 19 years. Masoud graduated from Ryerson University, Toronto, Canada and received a science of electronic engineering. However, different brands of pressure testing machines always have such problems: oil leakage, high noise, low efficiency, slow oil return speed and so on. Later, he graduated from Southern Methodist University, Dallas, Texas and received an MBA in Finance and marketing. (end)

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