CN3703

CN3703 is a PWM buck-mode three-cell lithium battery charge management IC that autonomously manages the charging of three series-connected lithium cells. It features a compact package, minimal external components, and ease of use. CN3703 is a PWM buck-type lithium battery charge management chip with CC/CV charging modes. The constant-current charge current is set by the current sense resistor R_CS connected between the CSP pin and the BAT pin. In CV mode, the battery voltage is 12.6V 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 8.4V, the charger automatically enters trickle charge mode, where the charge current is 15% of the programmed CC charge current. When the battery voltage rises above 8.4V, the charger enters CC mode, where the charge current is set by the internal 200mV reference voltage and the external resistor R_CS — i.e., the charge current equals 200mV/R_CS. As the battery voltage continues to rise and approaches the CV charge voltage, the charger enters CV mode and the charge current gradually decreases. When the charge current decreases to the value set by the EOC pin resistor, charging terminates and the DRV pin outputs a high level. The transistor inside one open-drain output pin turns off, presenting a high-impedance output; the transistor inside the other open-drain output pin turns on, pulling the output low to indicate the end-of-charge state. 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 12V, a new charge cycle will also start automatically. When the input voltage is removed, CN3703 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 the normal range. CN3703 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 charge voltage, the overvoltage comparator activates and turns off the external P-channel MOSFET, temporarily halting charging until the BAT pin voltage falls back below the CV charge voltage.

Applications

• Laptops, netbooks
• RC aircraft, cars, and boats
• 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 charging mode, battery voltage regulated at 12.6V with ±1% accuracy
• Constant current charging current set by external resistor
• For deeply discharged lithium batteries (battery voltage below 8.4V), trickle charging at 15% of the set constant current charging current
• Charge termination current settable by external resistor; charging terminates when current drops to the value set by the external resistor
• In charge termination state, a new charging cycle starts automatically when battery voltage drops to 12V
• Automatic sleep mode entry when input power is lost or input voltage falls below battery voltage
• Input undervoltage lockout
• Battery temperature monitoring
• Battery terminal overvoltage protection
• Charge status indication
• Wide input voltage range: 7.5V to 28V
• Complete charge management for 3-cell lithium batteries
• Charging current up to 5A
• PWM switching frequency: 300KHz
• Soft-start function
• Operating temperature range: -40°C to +85°C
• 16-pin TSSOP package
• Lead-free, halogen-free, RoHS compliant