How to achieve a portable product lithium battery

　　Author ：Iflowpower – Portable Power Station Supplier

Abstract: This article uses instances to explain how to achieve portable product batteries. Key words: portable product; linear regulator; buck-boost converter; battery in many portable products such as mobile phones, smart phones, digital media players, or digital cameras Development trend. This is usually implemented by using some of the more functions and more complex analog circuits, but the result is higher power consumption of the application circuit.

By new battery capacity can meet the increasing power consumption requirements, but this should be larger capacity battery or improved battery technology. Usually, people will not choose to increase the size of the battery because the outer casing is limited. Since the advancement of battery technology and the development of new technologies do not meet the high power requirements of the same size level, more advanced power management circuits should be more advanced.

At the same time, the demand for small solutions makes this challenge more difficult. In the past, in order to obtain the requirements, simply use several linear regulators. These regulators are directly connected to the battery to show the required system voltage rail.

Many power management units used in portable products have only used some linear regulators to control power consumption. Typical battery technology that has been applied is 3 NICD or NIMH battery packs. At the same time, these chemical properties have been almost all of them by a single lithium ion battery because these lithium-ion batteries have higher performance.

With many applications rising to current demand, some linear regulators have been replaced by more expensive but more efficient buck converters. Some of the power rails such as processor kernels and I / O are usually like this. Since the linear regulator and the buck converter can only adjust the output voltage when its input voltage is higher, if the battery voltage is lowered to the programmed output voltage, then the system is turned off.

The minimum pressure drop of the linear regulator or the pressure drop margin on the inductance and switch must be added to the output voltage. Therefore, there is a typical 3.3V voltage rail from a lithium-ion battery, and the typical battery voltage of the system is 3.

4V. The remaining electricity that occurs when dischased to 3.0V will not be used in this case.

Measurement shows that the remaining power in the current lithium ion battery is about 10%. That is to say, any power management solution that can use this remaining electricity must be capable of subtracting 10% efficiency after a higher than the buck converter resolution efficiency. In other words, any alternative solution using 97% average efficiency of a buck converter must be operated at least one more than 87% average efficiency to extend the run time for charging of a battery.

This is a huge challenge for many buck-boost converter solutions. General efficiency of SEPIC or reverse solutions for economic viable solution 85% maximum range. In order to obtain this efficiency, it has considered a method of using a variety of improved efficiency, such as synchronous rectification, and the size of this solution is larger than the buck converter.

4 Switch Bucking - Boot Conversion There is always two switches simultaneously switch, in a very optimized solution, using this buck converted will have the same efficiency (85%). Therefore, from this point of view, use a buck-boost converter does not work, and it is also because of this reason that people have never considered using this buck converter. However, there are some other challenges.

For example, mobile phones use high current pulses during data transmission to drive their RF-PA. These pulse currents can be obtained directly from the battery, which can cause additional pressure drop on the battery impedance and battery connector. Due to low supply voltages, this may cause the system voltage monitor to turn off the system when there is a current pulse.

LED applications based on LEDs in your phone, or start your hard drive in your media player application, you will have a similar impact on the battery. Due to aging or low temperature results in the new increase of battery impedance makes these problems more serious. In this case, the buck-boost converter can be used to deal with the voltage drop of the key system voltage rail.

This makes the system run more stable and reliable, and lower battery voltage discharge is also allowed. In addition, the battery is also improved. Typically, new battery capacity will accompany the use of a wider range of output voltages.

For example, with future lithium ion battery technology, the battery can be charged to up to 4.5 V, and can be discharged as low as 2.3V.

Take a middle voltage 3.4V, which can make the battery capacity is in an unused state. There are also battery technology that is in the development stage, will work well below 3.

4V (for example, Li-s). In this case, it will definitely step down - boost conversion. One simple way to solve this problem is to generate a higher system voltage rail (e.

g., 5V) that can be used to generate all system voltage rails, which are higher than the cutoff voltage of the battery. This work can be done by using a larger efficient boost converter and cascading converter.

Total power conversion efficiency can easily reach more than 90%. Unfortunately, more boost converters need more space, and usually do not have such space in portable handheld devices. Another option is to use a buck-boost converter to generate a system voltage rail directly from the battery.

As mentioned above, power conversion efficiency is a key factor in designing a competitive power management solution. Another important factor is the size of the solution. Considering this, a step-down-boosting switching solution based on Sepic or reverse topology is not suitable because it is more larger volumeless passive components, and is often low in efficiency.

A single inductive solution using 4 switches has the largest potential to meet these requirements. However, in a simple driver method, there are two switches at all times in operation at the same time, but use this solution not only sacrificed efficiency, but also improved the requirements of inductance and switch size, because there is flow through These components are higher RMS current. Only the side of these switches is only driven, which means always runs the device with a step-down or boost converter to achieve the highest efficiency, and the lower RSM current also brings the smallest solution size.

In this case, the buck and boosting conversion have the highest efficiency work point in two topologies. This is shown in the relationship example of the efficiency and boost (TPS61020) and buck (TPS62046) converter input voltage curve shown this. .