QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920 STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR LTC4080 Demonstration circuit 920 is a complete single easy hookup to an input supply and battery or cell Lithium-Ion battery charger and adjustable battery simulator. output voltage buck switching regulator. Operat- The high switching frequency of the voltage ing at a frequency of 2.25MHz, the 300mA syn- regulator allow tiny LC components to be used chronous regulator is powered from the Li-Ion and the 10-Pin 3mm x 3mm DFN thermally en- battery. hanced package with the metal backside allow This demonstration circuit allows the user to the linear charger to provide up to 500mA of quickly evaluate the LTC4080 performance. In- charge current in addition to the regulator out- dividual jumpers are provided for shutting down put current. the charger and/or the switching regulator, for Design files for this circuit board are available. selecting several regulated output voltages and Call the LTC factory. the mode of operation (fixed frequency or LTC and Burst Mode are trademarks of Linear Technol- Burst). LEDs indicate charger status (input ogy Corporation power and charge) and pins on the board allow Table 1. Typical Specifications (25C) Input Voltage Range V 3.75V to 5.5V IN Output Charger Float Voltage V (constant voltage mode) 4.2V 0.5% BAT Output Current I (constant current mode) 500mA 5% BAT Current Monitor Output 1V 1.5% Full Current Charge Termination Timer 4.5 Hours 25% C/10 Output Indication Level (CHRG) 50mA 10% 1.2V Regulator VOUT (100ma) 1.2V 2.5% 1.5V Regulator VOUT (100ma) 1.5V 2.5% 1.8V Regulator VOUT (100ma) 1.8V 2.5% 2.5V Regulator VOUT (100ma) 2.5V 2.5% Regulator Output Ripple Voltage (fixed frequency) 5mV p-p Regulator Output Ripple Voltage (burst mode) 50mV p-p Buck Regulator Maximum Output Current (fixed frequency) 350mA 500mA, although a lower charge current can The battery charger portion of demonstration be programmed by replacing the program re- circuit 920 uses a constant-current/constant sistor (R5) with a suitable value. Either a voltage charge algorithm with timer charge leaded resistor, from PROG to GND, or a 0402 termination. The battery float voltage is fixed at surface mount resistor can be used. 4.2V and the charge current is programmed for 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920 STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR Power and Charge LEDs indicate charger PROG terminal can be used to program differ- status. The Power LED indicates that the input ent charge current and also measure the voltage is greater than the undervoltage lock- charge current anytime in the charge cycle. out threshold level. The PROG pin voltage is directly proportional to the charge current where one Volt is equal The Charge LED has three states. With a bat- to full programmed current. tery connected, the LED is on when either trickle current is flowing (VBAT < 2.9V) or After the charge cycle has ended, if the battery when charge current greater than 10% of the voltage drops approximately 100mV, a new programmed value is flowing (VBAT > 2.9V). 2.25 hour recharge cycle will begin. When the battery voltage approaches the float The 2.25MHz synchronous buck regulator has voltage, the charge current will begin to drop. jumper selected output voltages of 1.2V, 1.5V, When it drops below 10%, the Charge LED 1.8V and 2.5V with output current up to goes out, indicating that the battery is near full 300mA. Jumpers are also provided for low charge. Charging continues until the timer quiescent current shutdown and for either fixed ends the charge cycle. During a trickle charge, frequency or Burst mode operation. Burst if the battery voltage does not exceed 2.9V af- mode provides high efficiency at low load cur- ter of the total charge time, the battery is rent. The input power for the regulator comes considered defective, charging ends and the from the BAT pin. Normally, a Li-Ion battery Charge LED flashes at a 2Hz rate. would be connected to the BAT pin, although With no battery connected, there is a condition the buck regulator can be operated without a where the Charge LED will be on with very lit- battery. When no battery is present, some ad- tle or no charge current flowing. This occurs ditional capacitance on the BAT pin may be with low input voltage. When the input voltage needed. Also, when the termination timer ends, exceeds approximately 3.5V, the Power and the BAT voltage will begin to drop. When it Charge LEDs come on. Above 4.3V, the drops below the recharge threshold, the timer Charge LED goes off. is reset and the charger output voltage returns to the float voltage of 4.2V. The charger jumper (JP1) can be used to shut down the charger and reset the timer. The 2