CN3801

CN3801 is a PWM step-down LiFePO₄ single-cell battery charge management IC capable of being powered by a solar panel, featuring trickle, constant current, and constant voltage charging modes. The constant current charge current is set by the current sensing resistor RCS between the CSP pin and BAT pin. In constant voltage mode, the charge voltage is 3.625V with an accuracy of 40mV. When the current output capability of the input power source decreases, the internal circuitry of CN3801 automatically tracks the maximum power point of the solar panel. Users do not need to account for worst-case conditions, allowing maximum utilization of the solar panel's output power, making it ideal for solar-powered applications. CN3801 operates normally when the VCC pin voltage exceeds the undervoltage lockout threshold, exceeds the battery voltage, and the MPPT pin voltage exceeds 1.23V. If the battery voltage falls below the trickle charge threshold, the charger automatically enters trickle charge mode, where the charge current is 17.5% of the programmed constant current. When the battery voltage rises above the trickle charge threshold, the charger enters constant current mode, where the charge current is set by an internal 120mV reference voltage and an external resistor RCS, i.e., charge current = 120mV/RCS. As the battery voltage continues to rise and approaches the constant voltage charge level, the charger enters constant voltage mode and the charge current gradually decreases. During charging, the transistor inside the open-drain output pin conducts and pulls the output low to indicate the charging status. When the charge current decreases to 16% of the constant current charge value, charging terminates and the DRV pin output goes high. The transistor inside one open-drain output pin turns off, leaving the output in a high-impedance state; the transistor inside another open-drain output pin conducts and pulls the output low to indicate charge termination. In the charge termination state, disconnecting and reconnecting the input power source initiates a new charge cycle; a new charge cycle also starts automatically if the battery voltage drops to the recharge threshold. CN3801 tracks the solar cell maximum power point using the constant voltage method. The maximum power point voltage is fed back to the MPPT pin through a resistive voltage divider. During maximum power point tracking, the MPPT pin voltage is regulated to 1.205V. When the input voltage drops, CN3801 automatically enters sleep mode and the internal circuitry shuts down. CN3801 also includes an internal overvoltage comparator. When the BAT pin voltage rises due to load variations or sudden battery removal, if the BAT pin voltage reaches 1.07 times the constant voltage charge level, the overvoltage comparator activates and turns off the external P-channel MOSFET, temporarily halting the charger until the BAT pin voltage falls back below 1.02 times the constant voltage charge level. Under certain conditions — such as when no battery is connected to the charger or the battery is suddenly disconnected — the BAT pin voltage may reach the overvoltage protection threshold; this is normal behavior.

Applications

• Handheld devices
• Emergency lighting
• Backup battery applications
• Portable industrial and medical instruments
• Power tools
• Standalone battery chargers
• Solar panel maximum power point tracking (MPPT)

Key features

• Other features include input undervoltage lockout, battery terminal overvoltage protection, and charge status indication
• 10-pin SSOP package