FAN5421: Single-Cell Li-Ion Switching Charger

The FAN5421 is a highly integrated switched-mode charger that minimizes single-cell Li-Ion charging time.

The charging parameters and operating modes are programmable through an I2C interface that operates up to 3.4 Mbps. The charger circuit switches at 3 MHz to minimize the size of external passive components.

The FAN5421 provides battery charging in three phases: conditioning, constant current, and constant voltage.

Charge termination is determined by a programmable minimum current level. A safety timer with reset control provides a safety backup for the I2C host.

The IC automatically adapts to current-limited power sources by reducing the charge current to keep the input supply above a programmed voltage (default 4.52 V).

The IC automatically restarts the charge cycle when the battery falls below an internal threshold. If the input source is removed, the IC enters a high-impedance mode with leakage from the battery to the input prevented. Charge status is reported back to the host through the I2C port. Charge current is reduced when the die temperature reaches 120°C.

The FAN5421 is available in a 1.96 x 1.87 mm, 20-bump, 0.4 mm pitch, Wafer-Level Chip-Scale Package (WLCSP).

Features

• Fully Integrated, High-Efficiency Charger for Single-Cell Li-Ion and Li-Polymer Battery Packs
• Faster Charging than Linear
• Charge Voltage Accuracy:
  • ∓0.5% at 25°C
  • ∓1% from 0 to 125°C
• ∓0.5% at 25°C
• ∓1% from 0 to 125°C
• ∓5% Charge Current Regulation Accuracy
• 20 V Absolute Maximum Input Voltage
• 6.8 V Maximum Input Operating Voltage
• 1.5 A Maximum Charge Rate
• Charge and Mode Programmable through High-Speed I2C Interface (3.4 Mb/s) with Fast Mode Plus Compatibility
  • Fast Charge / Termination Current
  • Charger Voltage
  • Safety Timer
  • Termination Enable
• Fast Charge / Termination Current
• Charger Voltage
• Safety Timer
• Termination Enable
• 3 MHz Synchronous Buck PWM Controller with Wide Duty Cycle Range
• Small-Footprint, 1µH External Inductor
• Safety Timer with Reset Control
• Low Reverse Leakage to Prevent Battery Drain to VIN