What is the charging voltage and current of lithium battery

The charging current and voltage of lithium battery vary dynamically, which is determined by the chemical substances of lithium battery itself. Therefore, it is necessary to configure the performance of charging IC according to the charging characteristics of lithium battery itself, so as to achieve correct, safe and efficient use of lithium battery. The "lithium battery charging current" in daily expression refers to the charging current of lithium battery in the rapid charging stage during the charging process. As a dynamic process, the optimal charging current of lithium battery is actually divided into three stages. Commonly used lithium battery charging IC such as TP4012A, TP8052, TP8056, the last part of this paper is introduced.

Performance description of several different charging states

1. Standby status:

Standby status is handled in the following situations:

A. The input voltage is lower than the minimum operating voltage of the circuit.

B. The battery voltage is fully charged.

C. Use the external switch to forcibly shut off IC and stop IC charging.

Voltage and current characteristics in standby state: charging IC has no charging voltage output, and IC input current is uA level, which can reduce circuit loss.

2. Pre-charging status: as shown in the figure above. The optimal current during pre-charging: that is, when the initial/no-load voltage of lithium battery is lower than the pre-charging threshold, it first passes through a pre-charging stage. For a single lithium ion battery, this threshold is generally 3.0v. In this stage, the pre-charging current is about 10% of the current in the next stage -- constant current charging stage.

3. Constant-current charging state: as shown in the figure above, when the battery voltage is higher than the preset voltage threshold and lower than the maximum voltage of 4.2v, IC will charge the battery with the maximum charging current set by the external resistor. Charge the battery voltage until it is equal to the maximum charging voltage (around 4.2v).

. Constant current is the best current when charging: the so-called constant current is the constant current, gradually increasing voltage, at this point into the stage of rapid charging. Most constant current charging current is set between 0.5 and 0.8c, which can be understood as 0.7c, that is, it can be filled in about two hours without considering other factors. The reason why I choose 0.7c is that this current achieves a good balance between charging time and charging safety.

Several problems needing attention in constant current charging state:

1. In this state, IC is in the state of maximum charging current and the loss is also the maximum. The loss calculation of linear step-down is equal to VIN-VOUT times IOUT. At this point, we need to pay attention to the highest working temperature of IC.

2. Because of the increase in temperature rise caused by the maximum charging current, IC will automatically reduce the maximum charging current. This is why charging current drops during overheating.

4. Constant voltage charging state: as shown in the figure above, when the battery voltage is detected equal to or close to the battery charging voltage, the maximum charging voltage is equal to or close to the battery charging voltage. At this time, the charging mode will be a constant 4.2v charging voltage and a gradual step-down charging current. When it is detected that the charging current is less than 1/10 of the maximum setting current, the charging will be stopped. Charge current during constant voltage charging: for a single lithium ion battery, when the battery reaches a certain voltage value, it enters constant voltage charging. The voltage value is generally 4.2v. At this stage, the voltage remains unchanged and the current decreases. This current decrease is a descending process in turn. Most lithium battery protection selects 0.1c as the termination current, which means that the charging process enters the end state. Once the charging is completed, the charging current drops to zero. In this state, it is necessary to pay attention to the problem that: when the battery is charged with a high maximum set voltage, it can be automatically turned off. At the same time, when the IC overvoltage protection point is in abnormal battery state, it can be automatically locked.

Lithium battery at the heart of the best charging current is constant current charging current design, want to stress here is that the most convenient type of lithium battery with appropriate design from 0.5 C to 0.8 C, such as: the iPhone's 1400 mAh capacity (mAh capacity = current mA x time h) batteries, for example, apple chose to 0.7 C, namely the apple charging current is 1 a or so more, most of the battery between 0.5 C, 0.8 C you can choose!

The maximum charging current of lithium battery is strictly determined by the battery structure. Therefore, the regulations of various lithium battery manufacturers are not consistent. Some are set at 0.6c, while the highest regulation of portable lithium battery is 1C.

Of course, the current design of pre-charging and constant-voltage charging cannot be ignored. In these two processes, if the initial voltage is not lower than the pre-charging threshold of 3.0v, there is no pre-charging process. In general, before and after the constant current charging process, there is a pre-incubation and movement recovery process conducive to the long-term use of lithium batteries.

Lithium battery charging management IC classification and application

IC classification of battery charging management:

According to the charging circuit structure, it can be divided into:

1. Linear step-down charging management IC:

Main types: TP4010, TP4011 TP4012, TP4013, TP4014, TP4015, TP4016.

The basic function of linear step-down is similar to the linear step-down circuit of LDO.

Maximum rechargeable current setting: it is generally set by means of constant current source plug-in resistance, and it is generally an internal integrated power device.

Main application fields: MP3, MP4, GPS, PMP, PDP

2. Switch step-down charging management IC:

Main model: TP8056, TP8052.

It also divided into synchronous and asynchronous step-down voltage.

Maximum rechargeable current setting: generally determined by the resistance sampling voltage drop in series in the charging circuit.

Main applications: large capacity NOTEBOOK batteries, NOTEBOOK batteries, all kinds of lithium battery packs