CN3722

CN3722 is a PWM buck-mode battery charge management IC that can be powered by a solar panel, featuring Maximum Power Point Tracking (MPPT). CN3722 supports constant-current/constant-voltage (CC/CV) charging, making it well-suited for charge management of single-cell or multi-cell lithium-ion or LiFePO₄ batteries. The constant-current charge current is set by a current-sense resistor R_CS connected between the CSP pin and the BAT pin. In CV mode, the constant voltage is set by an external resistor divider network. When the VCC pin voltage simultaneously satisfies all three conditions below: (1) VCC pin voltage is above the under-voltage lockout threshold (2) VCC pin voltage is above the battery voltage (3) VCC pin voltage is no less than the programmed maximum power point voltage the charger operates normally and charges the battery. If the battery voltage falls below 66.7% of the programmed CV charge voltage, 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 66.7% of the programmed CV charge voltage, the charger enters CC mode; the charge current is set by an internal 200mV reference voltage and 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 drops to 9.5% of the programmed CC charge current, the charger enters the charge termination state and the charge current goes to zero. CN3722 provides two status indicator pins: a charge status indicator pin and a charge termination indicator pin. During trickle charge, CC charge, and CV charge states, the internal transistor of one open-drain output pin is turned on, pulling the output low; the internal transistor of the other open-drain output pin is turned off, presenting a high-impedance state, indicating that charging is in progress. In the charge termination state, the internal transistor of the first open-drain output pin is turned off, presenting a high-impedance state; the internal transistor of the other open-drain output pin is turned on, pulling the output low, indicating charge termination. In the charge termination state, disconnecting and reconnecting the input power supply will initiate a new charge cycle. A new charge cycle will also start automatically if the battery voltage drops to the recharge threshold (95.8% of the CV charge voltage). CN3722 tracks the solar panel's maximum power point using the constant-voltage method. The maximum power point voltage is divided by two resistors and fed to the MPPT pin. During MPPT operation, the MPPT pin voltage is regulated to 1.04V. The MPPT pin regulation voltage has a temperature coefficient of −0.4%/°C, which closely matches the temperature coefficient of the solar panel's maximum power point voltage. When the input power is removed, CN3722 automatically enters sleep mode and the internal circuitry is shut down, reducing battery current consumption and extending standby time. 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. CN3722 also integrates an overvoltage comparator. When the BAT pin voltage rises — due to load changes, sudden battery removal, or other causes — and reaches 1.08 times the programmed CV charge 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 charge voltage. In certain situations, such as when no battery is connected to the charger or when the battery is suddenly disconnected, the BAT pin voltage may reach the overvoltage protection threshold. This is normal behavior.

Applications

• Solar cell charging
• Laptop computers
• Backup battery applications
• Portable industrial and medical instruments
• Power tools
• Standalone battery chargers

Key features

• Wide input voltage range: 7.5V to 28V
• Solar panel maximum power point tracking (MPPT)
• Complete charge management for single-cell or multi-cell Li-ion or LiFePO₄ batteries; constant voltage charge voltage set by external resistor divider network
• Charge current up to 5A
• PWM switching frequency: 300KHz
• Constant current charge current set by external resistor
• Trickle charging for deeply discharged batteries
• Battery temperature monitoring
• Charge status and end-of-charge status indication
• Soft-start function
• Battery terminal overvoltage protection
• Operating temperature range: -40°C to +85°C
• 16-pin TSSOP package
• Lead-free, halogen-free, RoHS compliant