CN3702

CN3702 is a PWM buck-mode dual-cell lithium battery charge management IC that autonomously manages lithium battery charging, featuring a compact package, minimal external components, and ease of use. CN3702 is a PWM step-down lithium battery charge management chip with constant current/constant voltage (CC/CV) charging modes. The constant current charging current is set by a current sense resistor R_CS connected between the CSP pin and the BAT pin. In CV mode, the battery voltage is 8.4V with 1% accuracy. When the VCC pin voltage exceeds the UVLO threshold and is greater than the battery voltage, the charger operates normally and charges the battery. If the battery voltage falls below 5.6V, the charger automatically enters trickle charge mode, where the charging current is 15% of the programmed CC charging current. When the battery voltage exceeds 5.6V, the charger enters CC mode, where the charging current is set by an internal 200mV reference voltage and an external resistor R_CS, i.e., charging current = 200mV/R_CS. As the battery voltage continues to rise and approaches the CV charging voltage, the charger enters CV mode and the charging current gradually decreases. When the charging current decreases to the value set by the EOC pin resistor, charging is complete and the DRV pin outputs a high level. The transistor inside one open-drain output pin turns off, placing the output in a high-impedance state; the transistor inside the other open-drain output pin turns on, outputting a low level to indicate the end-of-charge condition. In the end-of-charge state, disconnecting and reconnecting the input power supply will initiate a new charge cycle; if the battery voltage drops to the recharge threshold of 4V/cell, a new charge cycle will also start automatically. When the input voltage is removed, CN3702 automatically enters sleep mode and the internal circuitry is shut down. To monitor battery temperature, a 10kΩ NTC thermistor must be connected between the TEMP pin and the GND pin. If the battery temperature exceeds the normal range, charging will be suspended until the battery temperature returns to within the normal range. CN3702 also incorporates an overvoltage comparator. When the BAT pin voltage rises due to load changes or sudden battery removal, if the BAT pin voltage rises to 1.08 times the CV charging voltage, the overvoltage comparator activates and turns off the external P-channel MOSFET, temporarily halting the charger until the BAT pin voltage drops back below the CV charging voltage.

Applications

• Portable DVD players, walkie-talkies
• Laptop computers
• Backup battery applications
• Portable industrial and medical instruments
• Power tools
• Standalone battery chargers

Key features

• Constant-current and constant-voltage charging modes, suitable for lithium battery charging
• In constant-voltage mode, battery voltage regulated at 8.4V with ±1% accuracy
• Constant-current charge current set by external resistor
• Trickle charging for deeply discharged lithium batteries (battery voltage below 5.6V) at 15% of the programmed constant-current charge current
• Charge termination current programmable via external resistor
• Automatic new charge cycle initiated if battery voltage drops to 8V after charge termination
• Automatic sleep mode entry when input power is lost or input voltage falls below battery voltage
• Input UVLO, battery temperature monitoring, battery terminal overvoltage protection, and charge status indication
• 16-pin TSSOP package
• Wide input voltage range: 7.5V to 28V
• Complete charge management for 2-cell lithium batteries
• Charge current up to 5A
• PWM switching frequency: 300KHz
• Auto-recharge function
• Soft-start function
• Operating temperature range: -40°C to +85°C
• Lead-free, halogen-free, RoHS compliant