CONSONANCE CN3704

CN3704 is a PWM step-down lithium battery charge management IC featuring 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 BAT pin. In CV mode, the battery voltage is 16.8V 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 11.2V, the charger automatically enters trickle charge mode, where the charging current is 15% of the configured constant current. When the battery voltage rises above 11.2V, 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 toward the CV charging voltage, the charger enters CV mode and the charging current gradually decreases. When the charging current drops to the value set by the EOC pin resistor, charging is terminated and the DRV pin outputs a high level. The transistor inside one open-drain output pin turns off, entering 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 16V, a new charge cycle will also start automatically.

When the input voltage is lost, CN3704 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 GND pin. If the battery temperature exceeds the normal range, charging will be suspended until the battery temperature returns to within the normal range.

CN3704 also incorporates an overvoltage comparator. When the BAT pin voltage rises due to load changes or sudden battery removal, if the BAT pin voltage reaches 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.

• Constant current (CC) and constant voltage (CV) charging modes, ideal for lithium battery charging
• In CV mode, battery voltage is regulated at 16.8V with ±1% accuracy
• In CC mode, charging current is set via an external resistor
• For deeply discharged lithium batteries with voltage below 11.2V, trickle charging at 15% of the configured CC charging current
• During CV charging phase, charging current gradually decreases; charging terminates when current drops to the value set by the external resistor
• In end-of-charge state, a new charging cycle initiates automatically when battery voltage drops to 16V
• Automatic sleep mode entry when input power fails or input voltage falls below battery voltage
• Input undervoltage lockout
• Battery temperature monitoring
• Battery terminal overvoltage protection
• Charge status indication
• 16-pin TSSOP package
• Wide input voltage range: 7.5V to 28V
• Complete charge management for 4-cell lithium batteries
• Charging current up to 5A
• PWM switching frequency: 300KHz
• CC charging current set by external resistor
• End-of-charge current configurable via external resistor
• Auto-recharge function
• Soft-start function
• Lead-free, halogen-free, RoHS compliant

• Laptops, netbooks
• RC aircraft, car, and boat models
• Backup battery applications
• Portable industrial and medical instruments
• Power tools
• Standalone battery chargers