Briefly describe the battery technology of current portable electronic devices

Foreword

Today's portable electronic backup battery technology includes power detection algorithms, battery charging algorithms, and battery charging technology. As we all know, the rechargeable battery chemical reaction has four programs: nickel cadmium, nickel hydrogen, lithium ion, and lithium polymer. As a portable electronic device, although these four battery programs have their own characteristics, they are in terms of energy density and safety. Development and practice show that the advantages of lithium-ion batteries and lithium-polymer batteries have become ideal for small, long-running devices such as laptops and hard disk-based PMP. For portable electronic equipment engineers, the correct choice and application of battery technology in portable electronic equipment are of utmost importance. This article will discuss this and analyze the application examples.

1. Battery charging algorithm for trickle charging, fast charging, and stable charging

Depending on the energy requirements of the final application, a battery pack may contain up to four lithium-ion or lithium-polymer battery cells in a variety of configurations, with a mainstream power adapter: direct adapter, USB interface or car charging Device. These battery packs have the same charging characteristics, regardless of the number of cells, the configuration of the cells, or the type of power adapter. So their charging algorithms are the same. The best charging algorithms for lithium-ion and lithium-polymer batteries can be divided into three phases: trickle charging, fast charging, and stable charging.

Trickle charging. Used to charge deep-discharged cells. When the cell voltage is below about 2.8 volts, it is charged with a constant current of 0.1 degrees Celsius.

fast charging. When the cell voltage exceeds the threshold of trickle charging, the charging current is increased for fast charging. The fast charging current should be less than 1.0 degrees Celsius.

Stable voltage. During the fast charging process, once the cell voltage reaches 4.2 v, the steady voltage phase begins. At this time, the charging can be interrupted by a minimum charging current or a timer or a combination of the two. Charging can be interrupted when the minimum current is below approximately 0.07 degrees Celsius. The timer relies on a preset timer to trigger an interrupt.

Advanced battery chargers usually have additional safety features. For example, if the cell temperature exceeds a given window, typically 0°C - 45°C, charging will be suspended. In addition to some very low-end devices, the current Li-Ion/Li-Polymer battery charging solutions are integrated or have external components to charge according to the charging characteristics, not only for better charging. It is also for safety.

2.lithium ion / polymer battery charging program

The charging scheme for lithium ion/polymer batteries is different for different numbers of cells, cell configurations, and power types. There are currently three main charging options: linear, buck (buck) switches and SEPIC (boost and buck) switches.

2.1 linear scheme

When the charger input voltage is greater than the open circuit voltage after fully charged cells plus sufficient headroom, it is best to use a linear scheme, especially if the 1.0-degree Celsius fast charge current is not much greater than one. For example, an MP3 player usually has only one battery, and the capacity ranges from 700 to 1500 mah. The full charge open circuit voltage is 4.2 v. The power of the MP3 player is usually an AC/DC adapter or a USB interface, and its output is a regular 5 v; At this time, the linear solution charger is the simplest and most efficient solution. Figure 2 shows a linear scheme for a Li-Ion/Polymer battery charging scheme with the same basic structure as a linear voltage regulator.

Linear Solution Charger Application Example - Dual Input Li+ Charger and Smart Power Selector The MAX8677A.MAX8677A is a dual input USB / AC adapter linear charger with built-in SmartPowerSelector for powering from a rechargeable single-cell Li+ battery Portable device. The charger integrates all the power switches required for battery and external power charging and switching loads, eliminating the need for external MOSFET. The MAX8677A is ideal for portable devices such as Smartphones, PDAs, portable multimedia players, GPS navigation devices, digital cameras, And a digital video camera.

The MAX8677A can operate from a separate USB and AC adapter power input or any of two inputs. When connected to an external power source, the Smart Power Selector allows the system to be disconnected from the battery or can be connected to a deep discharge battery. The Smart Power Selector automatically switches the battery to system load and uses the unused input power section of the system to charge the battery, taking advantage of limited USB and adapter input power. All required current sensing circuits, including integrated power switches, are integrated on-chip. The DC input current limit is adjustable up to 2, while the DC and USB inputs support 100 mA, 500 mA, and USB suspend modes. The charge current can be adjusted up to 1.5 to support a wide range of battery capacitance. Other features of the MAX8677A include thermal regulation, overvoltage protection, charge status, and fault output, power good monitoring, battery thermistor monitoring, and charge timer. The MAX8677A is available in a space-saving, thermally enhanced, 4mm x 4mm, 24-pin TQFN package that is specified over the extended temperature range (-40 to + 85°C).

2.2 United States dollar(buck) switching programme

When the current charged at 1.0 degrees Celsius is greater than 1, or the input voltage is much higher than the fully open circuit voltage of the cell, the Buck or buck solution is a better choice. For example, in a hard disk-based PMP, a single-cell lithium-ion battery is usually used, with a full-fill open circuit voltage of 4.2 v and a capacity ranging from 1200 to 2400 mah. Now PMP is usually charged with a car kit, and its output voltage is between 9 and 16 v. A relatively high voltage difference (minimum 4.8 v) between the input voltage and the battery voltage will reduce the efficiency of the linear scheme. This inefficiency, coupled with a 1 c fast charge current greater than 1.2, can cause serious thermal issues. In order to avoid this situation, the Barker scheme is used. Figure 3 is a schematic diagram of the lithium ion/polymer battery Barker charger scheme. The basic structure is exactly the same as the Buck (buck) switching voltage regulator.

2.3 sepic (boost and buck) switching scheme

In some devices that use three or even four lithium-ion/polymer cells in series, the input voltage of the charger is not always greater than the battery voltage. For example, a laptop uses a 3-cell lithium-ion battery pack and is fully charged with an open circuit voltage. It is 12.6 v (4.2 vx3) with a capacity from 1800 mah to 3600 mah. The input power is either an AC/DC adapter with an output voltage of 16 v or a car kit with an output voltage between 9 and 16 v. Obviously, neither the linear nor the Buck scheme can charge this battery pack. This requires the SEPIC scheme, which works when the output voltage is higher than the battery voltage and also when the output voltage is lower than the battery.

3.electricity detection algorithm

Many portable products use voltage measurements to estimate the remaining battery power, but the relationship between battery voltage and residual power varies with power, temperature, and battery aging, making this method an error. The rate can be up to 50%. Market demand for longer-lasting products continues to increase, so system designers need more accurate solutions. Using a fuel gauge to measure the amount of battery charge or power consumed will provide a more accurate estimate of battery power over a wide range of application power levels.

3.1 One of the application examples of the power detection algorithm, the fully functional single and dual battery portable application battery pack design

The principle of electricity detection. A better fuel gauge must have at least battery voltage, battery pack temperature and current, measurement method; a micro-processing 9; and a set of proven power detection algorithms. The bq2650x and bq27x00 are fully functional fuel gauges with An analog-to-digital converter (ADC) that measures voltage and temperature and an analog-to-digital converter that measures current and charge sensing. These fuel gauges also have a microprocessor that is responsible for executing Texas Instruments' fuel detection algorithms. These algorithms compensate for the self-discharge, aging, temperature and discharge rates of lithium-ion batteries. The microprocessor included in the chip saves these computational burdens for the host system processor. The fuel gauge can provide information such as the remaining battery status. Bq 27x00 series products also provide the remaining run-time (RunTimetoEmpty). The host can query the fuel gauge at any time, and then inform the user of the battery information through the lead indicator or on-screen display. The fuel gauge is easy to use, and the system processor only needs to be configured with a 12 cor HDQ communication driver.

Battery pack circuit description. Figure 4(a) shows a typical battery pack application circuit with an identification function IC. Depending on the power meter IC used, the battery pack needs to have at least three to four external terminals. The VCC and bat pins are connected to the battery voltage to supply power to C and measure the battery voltage. A low-resistance sense resistor is connected to the battery ground to allow the high-impedance SRP and SRN inputs of the fuel gauge to monitor the voltage across the sense resistor. The current flowing through the sense resistor can be used to determine the amount of charge that the battery is charging or discharging. When the designer chooses to detect the resistance value, it must be considered that the voltage across the resistor should not exceed 100 mv. Too low a resistance value may cause an error when the current is small. The board layout must ensure that the connections from the SRP and SRN to the sense resistor are as close as possible to the sense resistor terminals, in other words, they should be wired in Kelvin.

The HDQ pin requires an external pull-up resistor that should be on the host or main application so that the gauge can enable sleep when the battery pack is disconnected from the portable device. It is recommended to use 10 kΩ for the pull-up resistor value.

Battery pack identification. The problem of inexpensive counterfeit batteries is becoming more and more serious. These batteries may not contain the safety protection circuit required by the OEM. Therefore, the genuine battery pack may include the identification circuit shown in Figure 4(a). When the battery is to be authenticated, the host sends an inquiry value (challenge) to the battery pack containing the IC (bq26150, which acts as a cyclic redundancy check (CRC). The CRC contained in the battery pack will be based on this query value and within the IC. The CRC polynomial is built to calculate the CRC value. The CRC is based on the host-based query command and the secretly defined CRC polynomial in the IC. The host also compares the CRC value calculation well with the battery pack to determine if the authentication is successful. By identification, the bq26150 will issue an instruction to ensure that the data line communication between the host and the fuel gauge is normal. When the battery connection is interrupted or reconnected, the entire authentication process will be repeated.

3.2 An example of a new type of integrated circuit that can be applied to a variety of General Electric meters

Many manufacturers today offer a wide range of fuel gauge IC, from which users can select the right functional devices to optimize the price/performance ratio of their products. Using a fuel gauge to store measured battery parameters, this split architecture allows the user to customize the fuel gauge algorithm within the host. This eliminates the cost of the embedded processor in the battery pack. This is a typical analysis of the DS2762 chip, exemplified by Dallas Semiconductor. A new type of separate fuel gauge integrated circuit, the structure of which is shown in Figure 5 (a).

DS2762 application features

The DS2762 is a single-cell lithium battery fuel gauge and protection circuit that is integrated into a tiny 2.46 mm x 2.74 mm flip chip package. Thanks to the integrated high precision resistors for power detection, this device is very space efficient. Its small size and unparalleled high integration are ideal for mobile phone batteries and other similar handheld products such as PDAs. The integrated protection circuit continuously monitors the battery for over voltage, under voltage, and overcurrent faults (during charging or discharging). Unlike the independent protection IC, the DS2762 allows the host processor to monitor/control the conduction state of the FET, so that the system power control can be achieved through the DS2762 protection circuit. The DS2762 can also charge a deeply drained battery when the voltage is less than 3 v, a current-recovery charging path is provided.

The DS2762 accurately monitors battery current, voltage, and temperature with dynamic range and resolution to meet the test standards of any popular mobile communications product. The measured current integrates the internally generated time base to achieve electricity metering. The accuracy of the fuel gauge is improved by real-time, continuous automatic offset correction. The built-in sense resistor eliminates resistance changes due to manufacturing process and temperature, further improving the accuracy of the fuel gauge. Important data is stored in 32 bytes, lockable eepm; 16 bytes of SRAM is used to store dynamic data. All communication with the DS2762 is performed through a one-line, multi-node communication interface, minimizing the connection between the battery pack and the host. Its main features are single-cell lithium battery protector; high-precision current (electrical energy metering), voltage and temperature measurement; optional integrated 25 mΩ sense resistor, each DS2762 is individually fine-tuned; 0 v battery resumes charging; 32 bytes Lockable eepm, 16-byte SRAM, 64-bit chip;

One-line, multi-node, digital communication interface; support multi-battery group power management, and realize system power control by protecting field effect transistors; in sleep mode, the supply current is only 2(maximum), and the operating current is 90(Maximum); 2.46 mm x 2.74 mm flip-chip package or 16-pin SSOP package, both with or without sense resistors; complex with an evaluation board.

4.Conclusion

The application of portable electronic battery technology is the basis for the selection of lithium-ion batteries and lithium polymer batteries and their chargers. How to choose the right one must also depend on the specific requirements of the portable electronic equipment.

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