Features

• Wide Input Voltage Range: Up to 32V (40V Absolute Maximum)
• Programmable Charge Current Up to 4A
• Selectable C/10 or Onboard Timer Termination
• Dynamic Charge Rate Programming/Soft-Start
• Programmable Input Current Limit
• 0.5% Float Voltage Accuracy
• 7.5% Charge Current Accuracy
• 4% C/10 Detection Accuracy
• NTC Resistor Temperature Monitor
• Auto-Recharge at 97.5% Float Voltage
• Auto-Precondition <70% Float Voltage
• Bad Battery Detection with Auto-Reset
• Average Current Mode, Synchronous Switcher
• User Programmable Frequency
• Low Profile (0.75mm) 5mm × 6mm 36-Pin QFN Package

Typical Application

Description

The LT®3651 is a 1 cell 4A Li-Ion/Polymer battery charger that operates with input voltages up to 32V. An efficient monolithic average current mode synchronous switching regulator provides constant current, constant voltage charging with programmable maximum charge current. A charging cycle starts with battery insertion or when the battery voltage drops 2.5% below the float voltage. Charger termination is selectable as either charge current or internal safety timer timeout. Charge current termination occurs when the charge current falls to one-tenth the programmed maximum current (C/10). Timer based termination is typically set to three hours and is user programmable (charging continues below C/10 until timeout). Once charging is terminated, the LT3651 supply current drops to 85μA into a standby mode.

The LT3651 offers several safety features. A discharged battery is preconditioned with a small trickle charge and generates a signal if unresponsive. A thermistor monitors battery temperature, halting charging if out of range. Excessive die temperature reduces charge current. Charge current is also reduced to maintain constant input current to prevent excessive input loading.

The LT3651 is available in a 5mm × 6mm 36-pin QFN package.