QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 531 LI-ION BATTERY CHARGER LTC4052 DESCRIPTION Demonstration circuit 531 is a complete pulse battery Input Power OK LED indicator (ACPR) charger designed to charge one Lithium-Ion cell. DC531 C/10 Charge LED indicator (CHRG) features the LTC4052 Li-Ion pulse charger with internal Small surface mount components are used to minimize MOSFET suitable for charging at a maximum current of board space and height with the circuitry occupying ap- 1A. proximately 0.15 square inches of board space with a Other Features include: height of 0.054 inches (1.4mm). Preset float voltage of 4.2V 1% Design files for this circuit board are available. Call Constant Current set by wall adapter current limit the LTC factory. Over current protection Table 1. Performance Summary 3-hour charge termination timer. This timer can be set PARAMETER VALUE for other time periods through a capacitor change. Input Voltage Range 4.5V to 10V For instance, you may want to use a much shorter pe- Output Voltage V 4.2V 1% BAT riod (on the order of 30 seconds) when evaluating the Output Current I (constant current mode) Up to 1A (determined by BAT board with a battery simulator instead of a Li-Ion bat- input supply current limit) tery. Output Current I (trickle current mode) 24mA 40% BAT Trickle charge for deeply discharged batteries C/10 CHRG LED Threshold Level 10% Duty Cycle Auto recharge when battery voltage drops below 4.05. Trickle Charge Threshold Voltage 2.45V Low battery drain current when the input supply is Battery Drain Current with V Removed 1A IN removed QUICK START PROCEDURE Demonstration circuit 531 is easy to set up to evaluate 4. Begin increasing the input voltage to 6V and keep the the performance of the LTC4052. Refer to Figure 1 for battery simulator power supply at 0V. Both LEDs proper measurement equipment setup and follow the (CHRG and ACPR) should have come on at approxi- procedure below: mately 2V, and the charge current should be approxi- mately 24mA. This is the trickle charge mode for a 1. Before connecting the input power supply to the de- deeply discharged battery. Typically, a battery that mo board, adjust the power supply current limit to has not been charged for a long time. 1A. Adjust the output voltage to 0V and then connect the power supply to the Vin and GND pins of the 5. Starting from 0V, slowly increase the battery simula- demo board. tor power supply (VBAT), observing the chargers output voltage on the DVM. When the chargers out- 2. Set the battery simulator to 0V, and then connect it to put voltage exceeds approximately 2.5V, the charger the BAT and GND pins. will suddenly enter the Constant current portion of the 3. Connect the digital voltmeters as shown in the setup charge cycle resulting in an abrupt increase in charge diagram to measure the input voltage V , charger IN voltage (VBAT) and the charge current (IBAT). 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 531 LI-ION BATTERY CHARGER current (IBAT) to the current limit of the input power 4.260V. The 60mV overvoltage is due to the (meas- supply. This is the constant current mode. ured) 60m resistance of the internal ESR of the bat- tery simulator power supply and associated wiring, 6. Continue to slowly increase the battery simulator and the 1A of charge current. The pulsing stops when power supply until the charge current pulsing begins. the lower portion of the charger voltage exceeds Approximately 3 seconds after the pulsing stops, the 4.200V 1% or the timer ends the charge cycle. CHRG LED turns off and stays latched off. 7. After the timer has timed out, slowly decrease the NOTE: When an actual battery is used, the battery volt- battery simulator power supply. At approximately age rises much slower than the battery simulator, re- 4.05V the charge current resumes and a new charge sulting in a very gradual decrease in pulse duty cycle. cycle begins. This is the Recharge Threshold Volt- When the duty cycle drops to 10%, the CHRG LED age. goes off, though there is still 40A flowing through the LED. NOTE: For evaluation purposes, the time can be de- creased from the programmed 3 hours to approxi- When the timer ends (3 hours for a 0.1F timing ca- mately 30 seconds by reducing the timer capacitor pacitor) the charge cycle ends and the CHRG pin be- (C4) from 0.1F to 270pF comes high impedance. Connecting a new battery or cycling the input power turns on the CHRG LED, start- 8. To verify battery drain current, remove the input sup- ing a new charge cycle. A new charge cycle also be- ply voltage. The ammeter that was reading charge gins if the battery voltage drops below 4.05V, though current now reads the battery drain current. A typical the CHRG LED is not on. value is less than 1A. When the charger is in the pulse mode, the DVM 9. To verify the overcurrent protection feature, adjust the reading appears to exceed the 4.2V Li-Ion float volt- battery simulator power supply to approximately 3.5V. age. This is because when the charger is pulsing, the Increase the current limit of the input power supply to LTC4052 monitors the chargers output voltage when approximately 2.5A. When the charge current reaches the charge current is not flowing. Because of the bat- the overcurrent threshold of approximately 1.9A, the tery and pack protection ESR, wiring and connector charge current immediately stops, waits for 640ms, resistance, the chargers output voltage will exceed then rises again, resulting in short pulses of current at the 4.2V float voltage when the charge current is flow- approximately 1.6Hz. These short pulses of current ing. represent an average current of approximately 1% of the overcurrent level of 1.9A. Figure 3 shows the Figure 2 shows typical waveforms when the battery is waveforms. near the end of the charge cycle. The charger output voltage, when charge current is flowing, approaches 2