Stand-Alone Switch-Mode Lithium-Ion Battery-Charger Controller

The MAX1737 is a switch-mode lithium-ion (Li+) battery charger that charges one to four cells. It provides a regulated charging current and a regulated voltage with only a ±0.8% total voltage error at the battery terminals. The external N-channel switch and synchronous rectifier provide high efficiency over a wide input voltage range. A built-in safety timer automatically terminates charging once the adjustable time limit has been reached.

The MAX1737 regulates the voltage set point and charging current using two loops that work together to transition smoothly between voltage and current regulation. An additional control loop monitors the total current drawn from the input source to prevent overload of the input supply, allowing the use of a low-cost wall adapter.

The per-cell battery voltage regulation limit is set between +4.0V and +4.4V and can be set from one to four by pin strapping. Battery temperature is monitored by an external thermistor to prevent charging if the battery temperature is outside the acceptable range.

The MAX1737 is available in a space-saving 28-pin QSOP package. Use the evaluation kit (MAX1737EVKIT) to help reduce design time.

Applications

* Desktop Cradle Chargers * Handheld Instruments (PDAs, Palmtops) * Li+ Battery Packs * Notebook Computers

* Stand-Alone Charger for Up to Four Li+ Cells

* ±0.8% Accurate Battery Regulation Voltage

* Low Dropout: 98% Duty Cycle

* Safely Precharges Near-Dead Cells

* Continuous Voltage and Temperature Monitoring

* < 1µA Shutdown Battery Current

* Input Voltage Up to +28V

* Safety Timer Prevents Overcharging

* Input Current Limiting

* Space-Saving 28-Pin QSOP

* 300kHz PWM Oscillator Reduces Noise

* 90% Conversion Efficiency