QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1068A DUAL INPUT LI-ION BATTERY CHARGER WITH SYNCHRONOUS BUCK REGULATOR LTC3550 Demonstration circuit 1068A is a complete sin- from each input power source individually, pro- gle cell Lithium-Ion battery charger and a syn- gramming the minimum charge current termina- chronous buck voltage regulator with adjustable tion level and two charge current levels when output voltage. Operating at a frequency of charging from USB power. 1.5MHz, the regulator can be powered from ei- The high switching frequency of the DC/DC ther the Li-Ion battery or from the AC adapter converter allow tiny LC components to be used (selected by a jumper). The battery charger and the 16-Pin 5mm x 3mm DFN thermally en- automatically selects input power from the AC hanced package with the metal backside allow adapter or USB port, which ever is appropriate. the linear charger to provide up to 950mA of charge current in addition to the regulators out- This demonstration circuit allows the user to quickly evaluate the LTC3550 performance. In- put current. The charge current on this board is dividual jumpers are provided for shutting down set for either 100mA or 500mA when powered the charger from either input power source, from USB power and 800mA when used with an shutting down the regulator and for selecting AC adapter. several regulated output voltages. Design files for this circuit board are available. LEDs indicate charger information (input power Call the LTC factory. and charge status) and terminals on the board LTC and Burst Mode are trademarks of Linear allow easy hookup to input supplies and battery Technology Corporation or battery simulator. Provisions are provided for programming and monitoring charge current Table 1. Typical Specifications (25C) Adapter and USB Input Voltage Range (Buck regulator powered from Battery) 4.25V to 8V Adapter Input Voltage Range (Buck regulator powered from Adapter Input) 4.25V to 5.5V Charger Output Float Voltage, V (constant voltage mode) 4.2V 0.5% BAT Charge Current, I from Adapter Input (constant current mode) 800mA 6% BAT Charge Current, I from USB Input (constant current mode) HPWR terminal High/Low 500mA/100mA 6% BAT Trickle Charge Current, I from Adapter Input (Battery Voltage <2.9V) 80mA 6% BAT Adapter and USB Current Monitor Output 1V 2.5% Full Current Charge Termination Threshold Current 50mA 10% C/x Output Indication Level LED (CHRG) 50mA 10% VOUT Regulator Output Voltage 1.2V, 1.8V, 2.5V (100mA Load) 2.5% VOUT Ripple Voltage (400mA Load) 18mV p-p VOUT Ripple Voltage Burst mode (Light Load) 80mV p-p Regulator Maximum Output Current 600mA 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1068A DUAL INPUT LI-ION BATTERY CHARGER WITH SYNCHRONOUS BUCK REGULATOR can shut down the charger. When USB power The battery charger portion of demonstration is present, the charger can be shut down by circuit 1068A uses a constant-current/constant moving the jumper to the middle position. The voltage charge algorithm with a programmable lower position enables the charger when either minimum charge current termination. The bat- input is used. tery float voltage is fixed at 4.2V and the charge current is programmed for 100mA, The IDC and the IUSB terminals can be used 500mA or 800mA, depending which power to measure the charge current that is being source is used and the status of the HPWR supplied from either input supply anytime in terminal. The charge cycle terminates when the charge cycle. The voltage on these pins is the charge current drops below 50mA after directly proportional to the charge current reaching the float voltage. Power and Charge where one Volt is equal to full programmed LEDs indicate charger status. The Power LED current. indicates the input voltage from either input The 1.5MHz synchronous buck regulator has power source is greater than the undervoltage jumpers to select output voltages of 1.2V, 1.8V, lockout threshold level and at least 180mV or 2.5V at up to 600mA of output current. Burst greater than the battery voltage. mode operation occurs at low load current and The Charge LED indicates a charge cycle is in automatically changes to continuous mode at progress. The LED is ON when the charger is high current. Burst mode provides higher effi- in the trickle current, constant current, or the ciency at low load current. constant voltage portion of the charge cycle The input power for the buck regulator can be (when the charge current is dropping). When from either the adapter input or from the bat- the charge current drops below the charge tery, selected by jumper JP2. Note that when termination current threshold level of 50mA, the regulator is powered from the adapter in- the LED goes off and the charge cycle ends. put, the maximum input voltage is limited to If the battery voltage drops approximately 5.5V. Normally, a Li-Ion battery would be con- 100mV from the float voltage, after the charge nected to the BAT pin, although the buck regu- cycle has ended, a recharge cycle will begin. lators can be operated without a battery. When no battery is present, some additional capaci- With power applied to the adapter input, plac- tance may be needed on the battery terminal. ing the EN Jumper (JP1) in the upper position 2