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Lithium battery charging IC-LP3947

by:dcfpower     2021-03-21

  charging IC-LP3947 is a built-in microprocessor, it is a fully functional single-cell lithium battery pack 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 for a stable power supply (LDO form), the output current can reach 1A, the battery with a stop voltage of 4.1V or 4.2V, constant current and constant voltage charging, and can precharge over-discharged batteries, built-in battery temperature detection, battery When the temperature is too high or too low, the charger automatically shuts off, has a 5.6-hour safety timer, has overcurrent and overheat 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℃.

   is a schematic diagram of its 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 prevent 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 output of the differential amplifier 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 type/charger type input terminal, if rechargeable battery is not installed, it will be LDO type, 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. 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. 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 the ground at this terminal.

  Charging process: The charger circuit composed of LP3947 is shown in Figure 2, and the charging process and charging status 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.< /p>

   When the charger is connected to the AC adapter or USB power supply, 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 , The pre-charging starts, the red LED is on, and the green LED is off.

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

   The charging current in the fast charging stage is 100mA when the ISEL terminal is connected to high level (USB mode), and when the ISEL terminal is connected to low level, the current is 500mA. If you use an AC adapter to charge at this moment, fast charge The 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 stage ends, and the charging is changed to 4.1V constant voltage charging. .

   The charging voltage remains unchanged during the constant voltage charging stage, but the charging current will gradually decrease until the charging current drops to a certain level, and 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 When the charging stop current can be set to 0.1C, the constant voltage charging current drops to 50mA, and the charging stops. At a fast charging current of 100mA, the timer reaches 5.6 hours and the charging stops, and both LEDs are on at this moment.

  The charging current is detected by the current detection circuit inside the IC, and the Diff-Amp output voltage (input to the ADC voltage of the microprocessor) in proportion to the charging current, and output a stop charging signal after being controlled by the microprocessor , The relationship between the charging current ICHG and the VDIFF of the Diff-Amp output voltage is:


   Note: the unit of the formula: current is A, voltage Is V.

  If you don’t remove the battery after stopping charging, it will enter the maintenance condition. When the battery voltage drops by 0.2V, supplementary charging will be carried out, and charging will stop when the charging voltage reaches 4.1V.

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