Engineer talk you something about battery level display

Twenty years ago, the fuel gauge IC did not appear. The earliest design was that the single chip microcomputer detected the battery voltage through the AD port to determine the remaining battery capacity. This method of voltage detection discharges the battery small current, and the battery power error is still accurate because If the voltage gradually decreases, just set a few fixed voltage points to judge, such as 100%, 75%, 50%, 25%, 10% voltage corresponding to several capacities, such as (Figure 1).

Correspondence table of voltage and capacity

Figure 1

If the large current is discharged, it is very unsuitable, because the large current discharge, the voltage fluctuation is relatively large, just like the early mobile phones, there are two grids of electricity before the call is displayed, and the power is directly prompted during the call, please charge in time .

charge in time

Figure 2

This has caused misunderstandings to consumers, saying that this is a problem with your product, and there are obviously two grids. Why can't you talk, ask for a return and exchange, etc. In fact, this has nothing to do with the design plan, because at that time only There are no other options for this kind of solution, and the battery material is not so stable and mature.

With the advancement of technology, battery materials are becoming more and more stable, and battery management ICs are springing up like mushrooms, innovation, and improvement. The most representative international companies are Texas Instruments and Meixin. Many high-end products on the market will use fuel gauge IC, so what is a fuel gauge? As the name implies, it is battery capacity calculation. It calculates the remaining capacity of the battery and the remaining working time. The fuel gauge IC has integrated measurement algorithms, such as coulomb counting, impedance tracking, and Kaman filtering. It can pass parameters such as current, voltage, temperature, and number of uses. Calculate how much capacity is left in the battery, how long it can be used, and remind the user to charge when the battery is low. Common fuel gauge ICs include BQ27541, DS2781, DS2782, BQ40Z50, etc. Why are batteries with fuel gauge ICs so expensive to sell? If you do not understand the production process of smart batteries, it may be one-sided understanding that the batteries are added to the board, added lines, and shipped after the battery comprehensive tester passes the test. In fact, the production of smart batteries is far less simple and much more complicated than this.

fuel gauge IC

Figure 3

First of all, starting from the battery protection board, how to let the motherboard know the battery information, then the protection board should be designed to communicate with the motherboard through communication, so that the motherboard needs what kind of information can be directly read fuel gauge IC storage Information, second, after designing the protection board, you need to learn CHEM_ID according to the battery cell required by the customer. What is CHEM_ID? ID is the aging data of many battery models integrated by Ti company, and then the number of each battery type is numbered. We learn this ID is to match the aging data of one of the batteries, so that the battery power model will be calculated according to the aging curve corresponding to this ID.

The battery pack with fuel gauge in the aging workshop of UFine is charging and discharging aging
(The battery pack with fuel gauge in the aging workshop of UFine is charging and discharging aging)

It is not easy to learn this ID. First of all, it is necessary to set up according to the parameters of the battery, and then calibrate the voltage, temperature, current; and then leave it at 0.2C for 2 hours, and then discharge at 0.2C until the over discharge protection is left for 5 hours; After getting the data, upload it to Ti's official website. Ti's official website will return a series of ID numbers. After selecting the appropriate ID number, write it to the fuel gauge IC, and then perform the aging test of the battery and the protection board for electricity calculation. 2 hours, then discharge at 0.1C to let stand for 5 hours, cycle twice, get the latest full charge capacity, battery impedance update, state change, just like BQ40Z50 two strings of protection boards, after successful learning, The impedance will be updated to 0055, and the Update Status will be updated to 0e. After learning is completed, as shown in Figure 3 and Figure 4; export batch files for batch use. After the aging data is protected and burned, after the battery is assembled and produced, the aging test of the charging and discharging cabinet is required to test the aging battery capacity. The whole production process is very complicated, not only the price of a single fuel gauge IC is 10 times more expensive than the ordinary protection IC, but also the battery assembly process is several times more complicated, so why the battery with communication is so expensive, but expensive Benefits, the device can accurately obtain the battery voltage, temperature, current, remaining capacity, remaining time and other information to avoid loss caused by the device shutdown.

Figure 4

Figure 4

The battery development trend of high-end electronic products in the future is definitely with a fuel gauge. Now no matter what industry you want to maximize the performance of the battery, from car batteries to small wearable devices batteries, you must be able to accurately estimate How much capacity is left in the battery and how much time is left, because the battery has already penetrated into our lives, and many things in our lives can't leave the battery!

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