Synchronous Buck Battery Charger LT3651-4.2 Performance Introduction

The LT3651-4.2's programmable switching frequency (200kHz to 1MHz) enables designers to balance solution size, power loss and filtering requirements. Synchronous operation achieves up to 90% charging efficiency. Final float voltage accuracy is 0.5%, charge current accuracy is 7.5%, and C/10 detection accuracy is 4%. Once charging is terminated, the LT3651-4.2 automatically enters a low current standby mode that reduces the input supply current to 80uA. In shutdown, the input bias current drops to 15uA. The LT3651-4.2 maximizes battery life by draining only <1uA from the battery during all non-charging cycles. For safety and autonomous charging control, the device includes automatic restart and preconditioning, a thermistor input for temperature-qualified charging, programmable input current limit, bad battery detection, and binary-coded status output pins.

The LT3651-4.2 is available in a low-profile (0.75mm) 36-pin 5mm x 6mm QFN package and is available in both E and I grades, guaranteed to operate from -40C to 125C. Pricing is $4.13 and $4.75 each, respectively, in 1,000-piece quantities. Two-cell 8.2V and 8.4V versions and a single-cell 4.1V version are planned to be available in the next 2 to 3 months.

Performance Summary: LT3651-4.2

Wide Input Voltage Range: 4.75V to 32V (40V Absolute Maximum Rating)

Programmable charge current up to 4A

Single-cell Li-ion/Polymer battery charging function, 4.2V charging voltage

Synchronous rectification improves charging efficiency

User Selectable Termination: C/10 or Programmable Termination Timer

Programmable Switching Frequency (200kHz to 1MHz)

Programmable Input Current Limit

0.5% charging voltage accuracy

7.5% Charge Current Accuracy

4% C/10 detection accuracy

NTC Resistor Temperature Monitors

Automatic recharging

Automatic preprocessing

Binary coded open collector charge status pin

Bad battery detection with automatic reset

Low-profile (0.75mm) 5mm x 6mm QFN-36 package