LTC4095EDC

The LTC4095EDC from Analog Devices is a complete linear battery charger for single-cell Li-Ion/Li-Polymer batteries, designed for USB and wall adapter power sources. The device integrates PowerPath control that automatically selects the best power source for the system – when a wall adapter or USB port is connected, the system is powered from the input while the battery charges; when the input is removed, the battery seamlessly powers the system through an internal switch, providing uninterrupted operation. The 1.2A maximum charge current (programmable via a single external resistor) supports fast charging from high-current wall adapters, while the USB compliance modes (100mA for USB default, 500mA when HPWR is asserted) prevent overloading the USB host. The CLS (current limit set) pin allows dynamic charge current adjustment based on the available input current, enabling priority sharing between the system load and battery charging. The battery float voltage is pin-selectable between 4.1V and 4.2V via the VSEL pin, accommodating different Li-Ion chemistry requirements. The thermal regulation loop monitors the junction temperature and automatically reduces the charge current when the temperature approaches the thermal limit, preventing thermal shutdown and allowing the charger to operate at the maximum safe charge current under all conditions. The NTC thermistor input (NTC pin) qualifies the battery temperature before and during charging, suspending charging if the battery is too hot or too cold. The CHRG open-drain output indicates charging status, and the ACPR output indicates input power presence. The compact 3x3mm DFN package minimizes board space for portable applications.

The LTC4095EDC operates as a linear Li-Ion battery charger with PowerPath control. Key subsystems include: (1) Linear Charger – a P-channel MOSFET pass transistor between the input (VCC) and battery (BAT) regulates the charge current and voltage; in constant-current (CC) mode, the pass transistor limits current to the programmed value (set by RPROG); when the battery reaches the float voltage (4.1V or 4.2V), the charger transitions to constant-voltage (CV) mode; as the battery charges, the current decreases; when it drops below C/10 (or the programmed termination threshold), charging terminates; (2) PowerPath Control – an internal switch connects either VCC (input) or BAT (battery) to the system output; when VCC is present and above the UVLO threshold, VCC powers the system through an internal ideal diode and the charger simultaneously charges the battery; when VCC is removed, the battery powers the system through a second ideal diode with minimal voltage drop; this provides seamless power source switchover with no system interruption; (3) USB Compliance – in USB mode (HPWR=low), the charge current is limited to 100mA; when HPWR is driven high (indicating a 500mA-capable port), the current limit increases to 500mA; when a wall adapter is detected (VCC > 5.5V or CLS pin driven), the full 1.2A charge current is available; (4) Thermal Regulation – an internal temperature sensor monitors junction temperature; if it exceeds approximately 105C, the charge current is reduced to maintain the temperature at the thermal limit; this prevents thermal shutdown while maximizing charge current under all thermal conditions; (5) NTC Qualification – an external NTC thermistor connected from the NTC pin to GND forms a voltage divider with an internal resistor; if the thermistor voltage indicates the battery is outside the 0-50C qualification window, charging is suspended.

• USB smart device: 100mA USB default, 500mA when host permits, 1.2A from wall adapter with seamless PowerPath switchover
• Portable medical: USB charging with NTC battery temperature qualification, 4.1V float for long cycle life
• USB peripheral with battery: internal Li-Pol battery charges from USB, PowerPath keeps system running when USB disconnected
• Handheld instrument: thermal regulation allows maximum safe charge rate in sealed enclosure