CR2450 battery

　　Definition of power management Analysis of power management design technology

　　Power management refers to how power is efficiently distributed to the different components of a system. Power management is critical for mobile devices that rely on battery power. A good power management system can double or triple battery life by reducing energy consumption when components are idle. Power management technology is also called power control technology. It belongs to the category of power electronics technology. It is an edge intersection technology that integrates power conversion, modern electronics, network construction, automatic control and other disciplines. It has been widely used in industry, energy, Transportation, information, special, special, education, culture and many other fields.

　　Power supply design technology

　　Q1: How to evaluate the power requirements of a system

　　Answer: For an actual electronic system, its power requirements must be carefully analyzed. Not only do you care about the input voltage, output voltage and current, but you also need to carefully consider the total power consumption, the efficiency of the power supply implementation, the transient response capability of the power supply part to load changes, the tolerance range of key components to power supply fluctuations, and the corresponding allowable Power ripple, heat dissipation issues, etc. Power consumption and efficiency are closely related. The higher the efficiency, the less the total power consumption will be when the load power consumption is the same, which is very beneficial to reducing the power budget of the entire system (compared to LDO and switching power supply, the efficiency of the switching power supply is higher). higher). It is worth noting that evaluating efficiency not only looks at the efficiency of the power circuit at full load, but also pays attention to the efficiency level at light load [2].

　　Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

　　Charging temperature: -20~45℃ -Discharge temperature: -40~+55℃ -40℃ Support maximum discharge rate: 3C -40℃ 3C discharge capacity retention rate ≥70%

　　Click for details

　　As for the load transient response capability, there are strict requirements for some high-performance CPU applications, because when the CPU suddenly starts to run heavy tasks, the required starting current is very large. If the power circuit response speed is not enough, causing a sudden The voltage drops too much, causing the CPU to run incorrectly.

　　Generally speaking, the actual value of the required power supply is mostly ±5% of the nominal value, so the allowable power supply ripple can be calculated based on this, of course, a margin must be reserved.

　　The heat dissipation issue is more important for those high-current power supplies and LDOs, and the suitability can also be evaluated through calculation.

　　Q2: How to choose a suitable power supply to implement the circuit

　　Answer: Based on the specific technical indicators obtained by analyzing the system requirements, you can choose the appropriate power supply to implement the circuit. The general weak current part includes LDO (linear power converter), switching power supply capacitor buck converter and switching power supply inductor capacitor converter. In comparison, LDO design is the easiest to implement and has small output ripple. However, the disadvantages are that the efficiency may not be high, the heat generation may be large, and the current that can be provided is not large compared with switching power supplies, etc. The switching power supply circuit design is flexible and efficient, but it has shortcomings such as large ripple, complicated implementation, and cumbersome debugging.

　　Low temperature and high energy density 18650 3350mAh-40℃ 0.5C discharge capacity ≥60%

　　Charging temperature: 0~45℃ Discharge temperature: -40~+55℃ Specific energy: 240Wh/kg -40℃ Discharge capacity retention rate: 0.5C Discharge capacity ≥ 60%

　　Click for details

　　Q3: How to choose appropriate components and parameters for switching power supply circuit

　　Answer: Many engineers who have never used switching power supply design will have a certain fear of it, such as worrying about interference problems of switching power supplies, PCBlayout problems, component parameter and type selection problems, etc. In fact, as long as you understand it, it is very convenient to use a switching power supply design.

　　A switching power supply generally consists of two parts: a switching power supply controller and an output. Some controllers integrate MOSFETs into the chip, which makes it easier to use and simplifies PCB design, but the design flexibility is reduced.

　　The switching controller is basically a closed-loop feedback control system. It generally has a sampling circuit for feedback output voltage and a feedback loop control circuit. Therefore, this part of the design is to ensure an accurate sampling circuit and control the feedback depth, because if the feedback loop response is too slow, it will have a lot of impact on the transient response capability.

　　The output part design includes output capacitors, output inductors, MOSFETs, etc. The selection of these components basically must meet a balance between performance and cost: high switching frequency allows the use of small inductance values (meaning small packaging and cheap cost), but a higher switching frequency will increase interference and increase the switching loss of the MOSFET, reducing the efficiency; a low switching frequency will bring exactly the opposite result.

　　The selection of the ESR of the output capacitor and the Rds_on parameter of the MOSFET is also very critical: choosing a small ESR can reduce the output ripple, but the cost of the capacitor will increase (good capacitors will be expensive). The driving capability of the switching power supply controller also needs attention: too many MOSFETs cannot be driven well.

　　Generally speaking, the supplier of switching power supply controller will provide specific calculation formulas and usage plans for engineers to learn from.

　　Q4: How to debug the switching power supply circuit

　　Answer: I have some experiences to share with you:

　　1: The input and output of the power circuit are connected to the board through a low-resistance high-power resistor. In this way, without soldering the resistor, the power circuit can be debugged first to avoid the influence of the subsequent circuit.

　　2: Generally speaking, the switching controller is a closed-loop system. If the output deterioration exceeds the controllable range of the closed-loop, the switching power supply will not work normally. In this case, the feedback and sampling circuits need to be carefully checked. What needs special attention is that if an output capacitor with a large ESR value is used, a lot of power supply ripple will be generated, which will also affect the operation of the switching power supply.

　　Discussion on grounding technology

　　Q1: Why is grounding necessary?

　　Answer: The introduction of grounding technology was originally a protective measure to prevent electric or electronic equipment from being struck by lightning. The method is to introduce the lightning current generated by lightning to the earth through lightning rods, thereby protecting buildings. At the same time, grounding is also an effective means to protect personal safety: when the phase line caused by some reason (such as poor wire insulation, aging lines, etc.) comes into contact with the equipment shell, dangerous voltage will be generated in the equipment shell. After grounding, The fault current generated will flow through the PE line to the earth, thus playing a protective role. With the development of electronic communications and other digital fields, it is no longer enough to only consider lightning protection and safety in the grounding system. For example, in a communication system, the interconnection of signals between a large number of devices requires that each device must have a base 'ground' as a reference ground for signals; as electronic devices become more complex, the signal frequency is getting higher and higher. Therefore, in In grounding design, special attention must be paid to electromagnetic compatibility issues such as mutual interference between signals (improper grounding will seriously affect the reliability and stability of system operation). In addition, the concept of "ground" is also introduced in the signal reflow technology of high-speed signals.

　　Q2: Definition of grounding

　　Answer: In the modern concept of grounding, to a line engineer, the term usually means the 'reference point of the line voltage'; to a system designer, it is often a cabinet or rack; to an electrical engineer, it is It means green safety ground wire or connected to the earth. A more general definition is "ground is a low-impedance path for current to return to its source" (note the requirements are "low impedance" and "path").

　　Q3: Common grounding symbols

　　Answer: PE, PGND, FG - protective ground or chassis; BGND or DC-RETURN - DC - 48V (24V) power supply (battery) return flow; GND - working ground; DGND - digital ground; AGND - analog ground; LGND - protection Mine protection area

　　Q4: Suitable grounding method

　　Answer: There are many grounding methods, including single-point grounding, multi-point grounding and mixed types of grounding. Single-point grounding is divided into series single-point grounding and parallel single-point grounding. Generally speaking, single-point grounding is used for simple circuits, ground differentiation between different functional modules, and low-frequency (f<1MHz) electronic circuits. When designing high-frequency (f>10MHz) circuits, multi-point grounding or multi-layer boards (complete ground plane layers) must be used.

　　Q5: Introduction to signal light reflow and cross-segmentation

　　Answer: For an electronic signal, it needs to find a circuit with the lowest impedance as a path back to the ground. Therefore, how to deal with the signal return becomes very critical.

　　First, according to the formula, we can know that the radiation intensity is proportional to the loop area. That is to say, the longer the path that the reflow needs to take, the larger the ring formed, and the greater its interference with external radiation. Therefore, when laying out the PCB Minimize the area of power loop and signal loop as much as possible.

　　Second, for a high-speed signal, providing better signal return can ensure its signal quality. This is because the characteristic impedance of the transmission line on the PCB is generally calculated with the ground layer (or power layer) as a reference. If there is a continuous ground plane near the high-speed line, the impedance of this line will remain continuous. If there is no ground reference near the segment line, the impedance will change because the discontinuous impedance will affect the integrity of the signal. . Therefore, when wiring, the high-speed lines should be allocated to a layer close to the ground plane or one or two ground wires should be run alongside the high-speed lines to provide shielding and provide reflow nearby.

　　Third, why it is said that when wiring, try not to separate it across power supplies. This is because after the signal crosses different power layers, its return path will be very long and it will be susceptible to interference. Of course, not all signals are strictly required not to be split across the power supply. Low-speed signals are acceptable because the interference generated can be ignored compared to the signal. High-speed signals must be carefully checked and try to avoid crossing by adjusting the wiring of the power supply part. (This is for the situation of multiple power supplies for multi-layer boards)

　　Answer: For general devices, it is best to ground them nearby. After adopting a multi-layer board design with a complete ground plane, grounding of general signals is very easy. The basic principles at this time are to ensure the continuity of the traces, reduce the number of vias, be close to the ground plane or power plane, etc.

　　Q6: Why should analog ground and digital ground be separated, and how to separate them?

　　Answer: Both analog and digital signals must return to ground. Because digital signals change quickly, they will cause a lot of noise on the digital ground, and analog signals need a clean ground to work as a reference. If the analog ground and digital ground are mixed together, the noise will affect the analog signal.

　　Generally speaking, analog ground and digital ground should be processed separately, and then connected together through thin traces or single points. The general idea is to try to prevent noise from the digital ground from flowing to the analog ground. Of course, this is not a very strict requirement that the analog and digital grounds must be separated. If the digital grounds near the analog part are clean, they can be connected together.

　　Q7: How are the signals on the board grounded?

　　Answer: For general devices, it is best to ground them nearby. After adopting a multi-layer board design with a complete ground plane, grounding of general signals is very easy. The basic principles at this time are to ensure the continuity of the traces, reduce the number of vias, be close to the ground plane or power plane, etc.

　　Q8: How are the interface devices of the single board grounded?

　　Answer: Some boards have external input and output interfaces, such as serial port connectors, network port RJ45 connectors, etc. If their grounding design is not good, it will also affect normal operation. For example, the network port interconnection may be incorrect. Phenomena such as coding and packet loss will also become sources of external electromagnetic interference, sending noise within the board outward. Generally speaking, an independent interface ground will be separated separately, and the connection with the signal ground is connected by thin wiring, and a 0 ohm or small value resistor can be connected in series. Thin traces can suppress signal ground noise from being transmitted to the interface ground. Similarly, the filtering of the interface ground and interface power supply must also be carefully considered.

　　Q9: How to ground the shielding layer of cables with shielding layer?

　　Answer: The shielding layer of the shielded cable must be connected to the interface ground of the single board instead of the signal ground. This is because there are various noises on the signal ground. If the shielding layer is connected to the signal ground, the noise voltage will drive the common mode current along the shield. This is why poorly designed cables are generally the largest noise output source of electromagnetic interference. Of course, the prerequisite for connecting the shielding layer to the interface ground is that the interface ground must also be very clean.

Read recommendations:

801738 450mAh 3.7V

Several misconceptions about lithium battery maintenance!1800mah 18650 battery

The main function of lithium battery protection board

551235 battery Vendor

r6 battery