Lithium Battery Charging IC-LP3947

Lithium battery charging IC-LP3947 is a built-in microprocessor, it is a fully functional single-cell lithium battery charging integrated circuit. It has a linear charging unit that can be powered by a USB interface or an AC power adapter and a built-in regulator tube. It can be used In Anwen power supply (LDO form), the output current can reach 1A, the battery with a voltage of 4.1V or 4.2V is stopped, constant current and constant voltage charging, and the over-discharged battery can be pre-charged, built-in battery temperature detection, battery temperature is too high When it is too low or too low, the charger automatically shuts down, has a 5.6-hour safety timer, over-current and over-heat protection, charging status indication, charging current detection, and outputs an analog voltage that is part of the charging current, and the device junction temperature TJ is at 0 ℃≤TJ≤85℃. Within the scale, the charging accuracy is within 1%, the input voltage scale: 4.3V—6.0V, when the AC adapter is powered, the charging current setting scale is 100mA—750mA, when the USB port is powered, the charging current setting scale is 100- 500mA. Working temperature: -40℃—+85℃.

The figure shows a schematic diagram of the pins. The IC can be widely used in mobile phones, digital cameras, USB-powered IT equipment and handheld appliances. The functions of each pin of LP3947 are explained as follows:

Pin1(EN): Charge input enable terminal, input high level to allow charging, low level to stop charging.

Pin2 (SCL): I2C serial interface clock input terminal.

Pin3 (SDA): I2C serial interface data input/output terminal.

Pin4 (BATT): Battery charging input terminal, this terminal is connected to a 10uF ceramic capacitor to the ground.

Pin5(VT): 2.78V stable voltage output terminal, a stable power supply for measuring battery temperature.

Pin6 (VBSENSE): battery voltage detection terminal, connected to the positive terminal of the battery.

Pin7 (MODE): Choose AC adapter power supply (set high level), choose USB power supply (set low level).

Pin8 (Diff-Amp): The differential amplifier output that detects the charging current. The output voltage is proportional to the charging current.

Pin9(Ts): Multi-function terminal, battery temperature detection input terminal, used for LDO form/charger form input terminal, if rechargeable battery is not installed, it is LDO form, used as low dropout 4.1V or 4.2V output voltage regulator Device.

Pin10 (EOC): Internal open-drain output. When the USB port or AC adapter is connected and the battery is full, this terminal outputs a low level, and an external LED can be connected to indicate that the battery is full.

Pin11 (GND): Ground terminal.

Pin12 (CHG): Internal open-drain output. When the USB port or AC adapter is connected, the battery starts to charge. This terminal outputs a low level, and an external LED can be connected to indicate that the battery has started to charge.

Pin13 (ISEL): The charger is powered by the USB port, this terminal is connected to high level, the charging current is 100mA, this terminal is connected to low level, and the charging current is 500mA (the charging current can be set for other I2C interfaces).

Pin14 (CHG-IN): Charger power supply input terminal, input a regulated power supply with current restriction, and a 1uF ceramic capacitor must be connected to ground at this terminal.

　　Charging process: The charger circuit composed of LP3947 is shown in Figure 2. The charging process and charging status indication are shown in Figure 3. The red LED is the charging indicator, and the green LED is the overflow indicator. The charging stop voltage in the figure is 4.1V.

The charger is connected to the AC adapter or USB power supply, and the charger starts to work. If the input voltage is at a low threshold voltage (≥4.3V) and a high voltage threshold voltage (≤6.0V), the charger detects a suitable input voltage, and the pre-charge starts, red The LED is on and the green LED is off.

The charging current in the pre-charging phase is between 40-70mA, so that the over-discharged battery can be safely charged with a small current. The battery voltage rises until the battery voltage rises above 3.0V. The pre-charging phase ends and the charging timer starts. Start charging.

The charging current of the fast charging stage is 100mA when the ISEL terminal is connected to a high level (USB mode), and when the ISEL terminal is connected to a low level, the current is 500mA. At this moment, if the AC adapter is used for charging, the fast charging current is set by the user (100 -750mA) The current accuracy of fast charging is ±20mA when ≤150mA, and ±10% when ≥200mA. When the fast charging voltage reaches 4.1V, the constant current charging phase ends, and it switches to 4.1V constant voltage charging.

During the constant voltage charging phase, the charging voltage remains unchanged, but the charging current will gradually decrease until the charging current drops to a certain level, the charging is over, at this moment the green LED is on and the red LED is off. If the fast charging current is 1C, the stop charging current can be set Set it to 0.1C, then the constant voltage charging current drops to 50mA, and the charging stops. At a fast charging current of 100mA, the timer expires for 5.6 hours and the charging stops. At this moment, both LEDs are on.

The charging current is detected by the IC's internal current detection circuit. Diff-Amp outputs a voltage that is in proportion to the charging current (input to the ADC voltage of the microprocessor). After being controlled by the microprocessor, the charging stop signal is output. The charging current ICHG and Diff- The relationship of VDIFF of Amp output voltage is:

　　ICHG=(VDIFF-0.497)/1.655

　Note: The unit in the formula: current is A and voltage is V.

　　 If the battery is not removed after the charging is stopped, it will enter the maintenance condition. When the battery voltage drops by 0.2V, the supplementary charging will be performed, and the charging will stop when the charging voltage reaches 4.1V.