LTC4054

The LTC4054L is a complete constant-current/constant-voltage (CC/CV) linear charger for single-cell lithium-ion batteries.

Its small size and ability to regulate low charge currents make it particularly suitable for portable applications using low-capacity rechargeable Li-Ion coin cells.

The LTC4054L is specifically designed to operate from power sources compliant with USB power specifications.

No external current-sense resistor or blocking diode is required because of its internal MOSFET architecture.

Thermal feedback automatically regulates the charge current to prevent overheating while maximizing the charging rate.

The charge voltage is preset to 4.2 V, while the charge current is programmed using a single external resistor.

After the final float voltage is reached, the LTC4054L automatically terminates the charging cycle when the charge current falls to 1/10 of the programmed value.

When the input supply is removed, the device automatically enters a low-current state, reducing battery drain to less than 2 µA.

In shutdown mode, supply current is limited to 25 µA maximum.

Key Features

• Programmable charge current: 10 mA to 150 mA
• Single-cell Li-Ion linear charger
• No external MOSFET required
• No external sense resistor required
• No blocking diode required
• Constant-current / constant-voltage operation
• Thermal regulation
• Preset 4.2 V charge voltage
• ±1% charge-voltage accuracy
• Charge-current monitor output
• Automatic recharge
• Charge-status output
• C/10 charge termination
• 2.9 V trickle-charge threshold
• Soft-start for reduced inrush current
• Shutdown supply current: 25 µA maximum
• Battery drain with input removed: <2 µA
• 5-lead low-profile SOT-23 / ThinSOT package

Applications

• Li-Ion coin-cell battery chargers
• Portable MP3 players
• Wireless headsets
• Bluetooth applications
• Multifunction wristwatches
• USB-powered portable devices

Repair note

The LTC4054L is a linear charger, not a switching charger. Therefore, the voltage difference between the input supply and battery voltage is dissipated as heat during charging.

A typical charging sequence is:

Precharge → Constant Current (CC) → Constant Voltage (CV) → C/10 termination → Automatic Recharge

The 2.9 V threshold is particularly important when diagnosing a deeply discharged battery. Below this level, the device enters the trickle/precharge region rather than immediately applying the programmed full charge current.

Tags: LTC4054, LTC4054-4.2, Li-Ion Charger, 1S, 4.2V, 800mA, SOT-23-5, SOT23-5, ThinSOT