Linear charging principle of high current lithium ion battery

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Overview:
Modern electronic products are becoming more portable and intelligent, and therefore require lightweight and efficient requirements for their power supply batteries. Lithium-ion batteries are gradually becoming the standard battery for modern electronic products because of their excellent performance, but lithium-ion batteries are more fragile than other batteries, so higher requirements are imposed on battery charging circuits. This paper introduces a smart high-current lithium-ion battery charging solution based on SE9018, which can meet the charging requirements of lithium-ion batteries in modern electronic equipment.

With the development of modern electronic technology, electronic devices are becoming more portable and multifunctional, and therefore, they are required to be lightweight and efficient. Lithium-ion batteries have gradually replaced traditional nickel-cadmium, nickel-hydrogen batteries and lead-acid batteries with their high energy density, excellent charge and discharge performance, and no pollution. They are widely used in modern portable electronic products. However, compared with other types of batteries, lithium-ion batteries have higher performance requirements for chargers. These requirements are mainly reflected in the control of the charging process and lithium battery protection, which is characterized by a large charging current. High-precision charging voltage, phased charging mode and perfect protection circuit. In response to the above requirements, Siwang Electronics has introduced an intelligent high-current lithium-ion battery charging chip SE9018.SE9018 with a PSOP8 package with a heat sink at the bottom. The number of peripheral components is small, which can be suitable for USB power supply and adapter power supply. It is modern. Ideal for portable mobile applications.

Figure 1 SE9018 pin map

Function introduction
The SE9018 is a constant current/constant voltage mode lithium-ion battery linear charging chip with an internal PMOSFET architecture and integrated anti-reverse charging circuit, eliminating the need for an external isolation diode. The chip preset charging voltage is 4.2V, the accuracy is ±1.5%, the charging current can be set by an external resistor, and the maximum continuous charging current can reach 1A. When the chip is due to large working power, high ambient temperature or poor PCB heat dissipation performance, etc. When the junction temperature is higher than 140 °C, the internal thermal feedback circuit will automatically reduce the charging current and control the chip temperature within the safe range. In order to enable the chip to maintain efficient operation, measures should be taken to minimize the chip operating power and chip temperature. For example, the input terminal is connected in series with a small resistor (reducing the input voltage), increasing the PCB heat dissipation copper foil area, and making the chip heat sink and PCB copper foil sufficient. Contact and so on.

Figure 2 Schematic diagram of SE9018
The SE9018 integrates a battery temperature monitoring circuit. When the battery temperature is outside the normal range (too high or too low), the chip automatically stops the charging process to prevent the battery from being damaged due to excessive or too low temperature. Battery temperature monitoring is achieved by determining the TEMP terminal voltage (VTEMP), which is provided by a resistor divider network that includes the internal NTC thermistor. When VTEMP is between 45%*VCC and 80%*VCC, the chip determines that the battery temperature is within the normal range; when VTEMP < 45%*VCC or VTEMP > 80%*VCC, the chip determines whether the battery temperature is too high or too low. When the TEMP terminal is grounded, the battery temperature monitoring function is disabled.

The SE9018 contains two open-drain status indication outputs CHRG and STDBY. When the circuit is in the charging state, the CHRG terminal is low and the STDBY terminal is high-impedance. When the battery is full, the CHRG terminal becomes high-impedance. The STDBY terminal is set low. When the battery temperature monitoring function is normally used, if the chip is not connected to the battery or the battery temperature is out of the normal range, the CHRG terminal and the STDBY terminal are both in a high impedance state; when the battery temperature monitoring function is disabled, if the chip is not connected to the battery, the STDBY terminal is Low level, CHRG terminal output pulse signal.

Other features of the SE9018 include manual shutdown, undervoltage lockout, automatic recharge, and more.
(Please read the PDF for details)