Analyze the selection method of lithium battery charging IC

Knowing that with the continuous development of hand-held transactions, the demand for battery chargers is also increasing. To select the appropriate integrated circuit (IC) for this task, we have to weigh several factors. At the beginning of planning, factors such as solution specifications, USB specifications, charging rate, and cost must be considered. In this article, we will analyze different charging topologies and discuss some characteristics of battery charger ICs. In addition, we will explore an application and existing solutions. Lithium battery charging cycle Lithium battery needs a special charging cycle to achieve safe charging and maximize battery life. There are two stages of battery charging: stable current (CC) and stable voltage (CV). When the battery is below the fully charged voltage, current enters the battery through a regulator. In the CC method, the current reaches one of two values u200bu200bthrough voltage stabilization. Assuming a very low battery voltage, the charging current drops to the pre-charge level to accommodate the battery and prevent battery damage. This threshold varies with the chemistry of the battery and generally depends on the battery manufacturer. Once the battery voltage exceeds the pre-charge threshold, the charge rises to the fast charge current level. Generally, the maximum recommended fast charging current for a battery is 1C (C u003d the current required to deplete the battery in an hour), but this current also depends on the battery manufacturer. The typical charging current is ~0.8c to maximize battery life. When the battery is charged, the voltage rises. When the battery voltage rises to a stable voltage (generally 4.2v), the charging current gradually decreases and the battery voltage tends to stabilize, preventing overcharging. In this way, when the battery is charged, the current gradually decreases and the battery impedance decreases. Assuming that the current drops to a predetermined level (usually 10% of the fast charging current), charging is terminated. We generally do not float the battery to charge, because this will shorten the battery life. Figure 1 illustrates a typical charging cycle. There are two topologies for converting adapter voltage to battery voltage and controlling different charging stages: linear regulator and inductive switch. These two topologies have their own advantages and disadvantages in terms of size, power, solution cost, and electromagnetic interference (EMI) radiation. Let's take a look at the various advantages and disadvantages of these two topologies. In general, the inductive switch is the best choice for the highest power. Use detection elements such as resistors to detect the charging current at the output. When the charger adopts the CC mode, the current echo circuit controls the duty cycle. The duty cycle under the CV method is controlled by the battery voltage detection echo circuit. Depending on the feature set, some other control loops may appear. We will review these cycles in detail later. Inductive switching circuits need switching elements, rectifiers, inductors, and input and output capacitors. For many applications, the specifications of the solution can be reduced by choosing a device that incorporates the switching component and rectifier into an integrated circuit. Depending on the load, the typical power of these circuits is 80% to 96%. Switching converters usually require more space and are more expensive because of their inductance specifications. Switching converters also cause electromagnetic radiation from the inductor and noise at the output of the switch. The linear charger reduces the input voltage of the bypass element, and the DC voltage drops. The advantage of this is that the solution requires only three components: a bypass component and an input/output capacitor. Compared with inductive switches, linear voltage drop regulators (LDOs) are usually a low-cost, low-noise solution. The current enters the battery through the resistor of the bypass component of the regulator, and then controls the charging current. The current response generally comes from the input of the charger IC. Test the battery voltage to supply the CV response. Change the resistance of the bypass element to maintain a stable current input into the integrated circuit or stabilize the battery voltage. The input current of the device is equal to the load current. This means that the power of the solution is equal to the ratio of the output voltage to the input voltage. The disadvantage of the LDO solution is that the power is low at a high I/o voltage ratio. All power is consumed by the bypass components, which means that LDO is not an ideal choice for applications with high charging currents and large differences in input and output. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Analysis of the principle of lithium battery charging