TI电池管理芯片--电池术语解码3

1万 · 2020-5-26 19:19

本帖最后由 xyz549040622 于 2020-5-26 19:21 编辑

I went through many battery terms and acronyms in part 1 and part 2 of this blog series, but now let’s talk about the most common acronym related to lithium-ion (Li-Ion) battery fuel gauging: SOC. You may already know this as state of charge (not system on chip, which is also commonly used for certain semiconductors).

When you look at your phone or another portable device, your battery gauge is fairly intuitive: 100% means your battery is fully charged and 0% means that it’s empty. While it seems simple, the magic behind that number is much more complicated. SOC is actually a relative number; it depends on multiple factors like your system characteristics, the battery’s age, the temperature and the load you will pull from it. In a sense, the fuel gauge is trying to predict the future, but it can’t tell whether you will be recording a video (heavy load) or listening to music (light load), or whether the temperature will be warm or cold.

SOC is expressed as a percentage, calculated as SOC = RM/FCC. Remaining capacity (RM) represents how much energy you will likely be able to extract from the battery from the current point in time until the system can no longer operate. Full-charge capacity (FCC) is the total amount of energy you could extract from the fully charged state until empty.

Figure 1: Usable capacity depends on internal impedance

Figure 1 illustrates these concepts. It’s essentially a voltage curve showing the discharge of a single lithium-ion cell. The y-axis is the voltage and the x-axis represents an integration of the current removed from the cell in milliamp hours (mAh). The open-circuit voltage (OCV) curve shows an unloaded or very lightly loaded voltage profile.

The key points on Figure 1 are the full points and the empty points. Every system will charge the battery to a different full point (so obviously that will affect FCC) and every system design will consider empty to be at different voltages. Let’s call the empty voltage “terminate voltage” (also sometimes called end-of-discharge voltage [EDV]).

Figure 2: Usable battery capacity is variable

Notice how Figure 2 shows a lower-voltage curve. Because of Ohm’s law, the voltage drop will be lower if either the load current (I) or resistance (R) increases. The load current depends on your system and what functions it is performing, and the resistance depends on the cell characteristics, the temperature, the age and the amount of charge in the cell. These are of course highly variable, which makes the job of fuel gauging very tricky.

The main takeaway from Figure 2 is that you get different amounts of energy out of a battery at different loads, temperatures, ages and so on. Most systems are used at different temperatures and their loads are typically very dynamic; so essentially, the voltage curve you are riding on will be shifting continuously. RM and FCC will both be changing – and not always by the same ratio – so SOC can also change. For example, because of increased internal impedance, a battery will technically have a higher SOC when it is warm than when it is cold.

Most system designers assume that end users don’t know the physics and chemistry behind these miracle “portable energy sources” called batteries. They don’t want to confuse users by having SOC jump up when they haven’t actually charged it, so they often filter, smooth or otherwise apply some kind of technique to the raw gauge data to present a more “intuitive” – but less accurate – SOC. Discussions of how TI’s Impedance Track™ gauges handle such SOC smoothing is a topic for another day, but let’s shift gears to bring this home.

Besides the fuel gauge in your car’s dashboard showing how much gasoline is in your tank between F and E, your car might also have a display to show you how many miles or kilometers you can travel until you hit empty. How reliable have you found that display? You’ve probably noticed that it can change a lot, but have you ever wondered why? The car’s computer is trying to predict the future, just like a battery fuel gauge. But a gauge doesn’t have a crystal ball, so it has to base its predictions on something. Most gauges base predictions on recent history like frequent highway driving or constantly driving uphill, since both activities require different amounts of fuel.

Now that you know a little more about the complexity behind the curtains, you might be able to make more informed use of the information that fuel gauges report, whether it’s in your phone, your computer or your car.

Additional resources

If you need a fuel gauge for your next battery-powered product:
Start with the selection tool here.
Ask for a recommendation on the TI E2E™ Community Battery Management – Gas Gauge forum.
For more insight into battery characteristics and how they affect fuel gauging, check out Single Cell Gauging 101: Battery Chemistry Fundamentals (17:03).

1万 · 2020-5-26 19:22

[tr]我看了很多电池术语和缩略语[tr]第一部分[tr]和[tr]第二部分[tr]这个博客系列，但现在让我们谈谈最常见的缩略词锂离子(锂离子)电池燃料计量：SoC。你可能已经知道这是一种电荷状态(不是晶片上的系统，这也是某些半导体常用的)。

[tr]当你看你的手机或其他便携式设备时，你的电池计量器是相当直观的：100%意味着你的电池已经完全充电，0%意味着它是空的。虽然看起来很简单，但这个数字背后的魔力要复杂得多。SoC实际上是一个相对的数字，它取决于多个因素，如您的系统特性，电池的年龄，温度和负载，您将从它。从某种意义上说，燃油计量器正试图预测未来，但它无法判断你是在录制一段视频(沉重的负荷)，还是在听音乐(轻负荷)，或者温度是温暖的还是寒冷的。

[tr]SoC表示为百分比，计算为SOC=RM/FCC。剩余容量(RM)是指在系统无法运行之前，你很可能能够从当前时间点从电池中提取多少能量。全电荷容量(Fcc)是指你可以从充满电荷的状态中提取到空的总能量。

图1：可用容量取决于内部阻抗

[tr]图1展示了这些概念。它本质上是一个显示单个锂离子电池放电的电压曲线。y轴是电压，x轴代表毫安小时内从电池中移除的电流的积分(MAh)。开路电压(OCV)曲线显示无负载或极轻负载电压剖面.

[tr]图1中的关键点是完整点和空点。每个系统将充电到一个不同的完整点(这显然会影响FCC)和每个系统的设计将考虑在不同的电压。让我们称空电压为“终止电压”(有时也称为结束放电电压[edv])。

图2：可用电池容量是可变的

[tr]请注意图2如何显示低电压曲线.由于欧姆定律，当负载电流(I)或电阻(R)增大时，电压降会降低。负载电流取决于系统及其所执行的功能，电阻取决于电池特性、温度、电池的年龄和电荷量。这些当然是高度可变的，这使得燃料测量的工作非常棘手。

[tr]图2的主要优点是，在不同的负载、温度、年龄等情况下，电池的能量是不同的。大多数系统都是在不同的温度下使用的，它们的负载通常是非常动态的；因此，从本质上说，您所乘坐的电压曲线将不断地发生变化。RM和FCC都将发生变化--而不是总是以相同的比例--因此SOC也可以改变。例如，由于内部阻抗的增加，电池在技术上会比冷的时候有更高的SOC。

[tr]大多数系统设计者认为，终端用户不知道这些神奇的“便携式能源”--电池--背后的物理和化学。他们不想让SOC在没有充电的情况下跳起来来迷惑用户，所以他们通常会过滤、平滑或以其他方式将某种技术应用于原始的量规数据，从而呈现出更“直观”但不太准确的SOC。讨论如何[tr]TI阻抗轨道™量规[tr]处理这样的SOC平滑是另一天的话题，但让我们换个角度把它带回家吧。

[tr]除了你的汽车仪表盘上显示F和E之间的油箱里有多少汽油外，你的车还可以显示出你可以行驶多少英里或公里，直到你撞空为止。你发现那个显示器有多可靠？你可能已经注意到它可以改变很多，但你有没有想过为什么？这辆车的电脑正试图预测未来，就像电池燃料计量器一样。但是一个量规没有水晶球，所以它的预测必须建立在某种东西的基础上。大多数预测都是基于最近的历史，比如频繁的高速公路驾驶或不断地上山，因为这两种活动都需要不同数量的燃料。

[tr]既然你对窗帘背后的复杂性有了更多的了解，你就可以更好地利用油量报告中的信息，无论是在你的手机里，还是你的电脑里，还是你的车里。

TI电池管理芯片--电池术语解码3

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