Linear lithium battery charging management chip suitable for portable device applications

　　The CN3052A/CN3052B/CN3056 introduced in this article is a high-performance linear lithium battery charging management chip. These devices have integrated power tubes, do not require external current detection resistors and blocking diodes, only require very few peripheral components, and comply with USB bus technical specifications. They can charge lithium batteries through USB ports, so they are very suitable for various chargers and portable products such as MP4 players, Bluetooth headsets, digital cameras, etc. Figure 1 is a typical application circuit diagram.

　　Figure 2 is the internal functional block diagram of CN3052A/CN3052B/CN3056, and the pin functions of the chip are shown in Table 1. The thermal modulation circuit can control the chip temperature within a safe range when the device power consumption is relatively large or the ambient temperature is relatively high, which is convenient for customers' system design. The modulated output voltage is 4.2V with an accuracy of 1%; the charging current can be adjusted by an external resistor. When the input voltage is too low or the power is off, CN3052A/CN3052B/CN3056 automatically enters a low-power sleep mode, and the battery current consumption is less than 3uA.

Working process of CN3052A/CN3052B/CN3056

　　Figure 3 is a schematic diagram of the charging process of CN3052A/CN3052B/CN3056. When the input voltage is greater than the power supply low voltage detection threshold and the chip enable input terminal is connected to a high level, CN3052A/CN3052B/CN3056 starts to charge the battery, and the CHRG pin outputs a low level, indicating that charging is in progress. If the battery voltage is lower than 3V, the charger pre-charges the battery with a small current. When the battery voltage exceeds 3V, the charger charges the battery in constant current mode, and the charging current is determined by the resistor RISET< between the ISET pin and GND. When the battery voltage approaches the battery terminal modulation voltage of 4.2V, the charging current gradually decreases, and CN3052A/CN3052B/CN3056 enters the constant voltage charging mode.

　　When the charging current decreases to the charging end threshold, the CHRG terminal outputs a high impedance state, indicating that the charging cycle is over. The charging end threshold is 10% of the constant current charging current. If you want to start a new charging cycle, just turn off the input voltage and then turn it on again, or temporarily pull the voltage of the CE pin to 0V and then restore it to a high level. When the battery voltage drops below the recharge threshold, a new charging cycle starts automatically. When the input voltage is lower than the battery voltage, the charger enters a low-power sleep mode, and the current consumed by the battery end is less than 3uA, thereby increasing the standby time. If the enable input CE is connected to a low level, the charger is turned off.

Introduction to the main functions of CN3052A/CN3052B/CN3056

　　Power supply low voltage detection (UVLO) CN3052A/CN3052B/CN3056 has an internal power supply voltage detection circuit. When the power supply voltage is lower than the power supply voltage too low threshold (typical value 4.03V), the chip is in the shutdown state and charging is also prohibited.

　　Sleep mode CN3052A/CN3052B/CN3056 has a sleep state comparator inside. When the input voltage VIN is less than the battery terminal voltage +40mV, the charger is in sleep mode; only when the input voltage VIN rises to more than 90mV of the battery terminal voltage, the charger can leave the sleep mode and enter the normal working state.

　　Pre-charge state At the beginning of the charging cycle, if the battery voltage is lower than 3V, the charger is in the pre-charge state, and the charger charges the battery at 10% of the constant current charging mode charging current.

　　Set the charging current The constant current mode charging current of CN3052A/CN3052B/CN3056 can be set by the resistance of the ISET pin. Charging current:

　　Thermal modulation function CN3052A/CN3052B/CN3056 has an integrated thermal modulation circuit. When the temperature of the chip rises to a certain temperature (115℃), the thermal modulation circuit starts to work and maintains the temperature of the chip at 115℃, which is in a constant temperature state. This function is very important for linear charger circuits, and it can even be said to be indispensable. With this function, users only need to consider the normal situation when designing the maximum charging current, without considering the worst working condition. If there is no thermal modulation function, users must fully consider the worst situation when designing the maximum charging current, otherwise the chip will be burned due to overheating.

Figure 1: Typical application circuit diagram of CN3052A/CN3052B/CN3056

Figure 2: Internal functional block diagram of CN3052A/CN3052B/CN3056

Figure 3: CN3052A/CN3052B/CN3056 charging process diagram

Table 1: CN3052A/CN3052B/CN3056 pin function description