QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 531 LI-ION BATTERY CHARGER LTC4052 DESCRIPTION Demonstration circuit 531 is a complete pulse battery charger designed to charge one Lithium-Ion cell. DC531 features the LTC4052 Li-Ion pulse charger with internal MOSFET suitable for charging at a maximum current of 1A. Other Features include: Preset float voltage of 4.2V ±1% Constant Current set by wall adapter current limit Over current protection 3-hour charge termination timer. This timer can be set for other time periods through a capacitor change. For instance, you may want to use a much shorter period (on the order of 30 seconds) when evaluating the board with a battery simulator instead of a Li-Ion battery. Trickle charge for deeply discharged batteries Auto recharge when battery voltage drops below 4.05. Low battery drain current when the input supply is removed Input Power OK LED indicator (ACPR) C/10 Charge LED indicator (CHRG) Small surface mount components are used to minimize board space and height with the circuitry occupying approximately 0.15 square inches of board space with a height of 0.054 inches (1.4mm). Design files for this circuit board are available. Call the LTC factory. Table 1. Performance Summary PARAMETER VALUE Input Voltage Range 4.5V to 10V Output Voltage VBAT 4.2V ±1% Output Current IBAT (constant current mode) Up to 1A (determined by input supply current limit) Output Current IBAT (trickle current mode) 24mA ±40% C/10 CHRG LED Threshold Level 10% Duty Cycle Trickle Charge Threshold Voltage 2.45V Battery Drain Current with VIN Removed 1µA QUICK START PROCEDURE Demonstration circuit 531 is easy to set up to evaluate the performance of the LTC4052. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. Before connecting the input power supply to the de- mo board, adjust the power supply current limit to 1A. Adjust the output voltage to 0V and then connect the power supply to the Vin and GND pins of the demo board. 2. Set the battery simulator to 0V, and then connect it to the BAT and GND pins. 3. Connect the digital voltmeters as shown in the setup 4. Begin increasing the input voltage to 6V and keep the battery simulator power supply at 0V. Both LEDs (CHRG and ACPR) should have come on at approximately 2V, and the charge current should be approximately 24mA. This is the trickle charge mode for a deeply discharged battery. Typically, a battery that has not been charged for a long time. 5. Starting from 0V, slowly increase the battery simula- tor power supply (VBAT), observing the charger’s output voltage on the DVM. When the charger’s output voltage exceeds approximately 2.5V, the charger will suddenly enter the Constant current portion of the charge cycle resulting in an abrupt increase in charge diagram to measure the input voltage VIN, charger 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 supply. This is the constant current mode. 6. Continue to slowly increase the battery simulator power supply until the charge current pulsing begins. Approximately 3 seconds after the pulsing stops, the CHRG LED turns off and stays latched off. NOTE: When an actual battery is used, the battery volt- 4.260V. The 60mV overvoltage is due to the (measured) 60mΩ resistance of the internal ESR of the battery simulator power supply and associated wiring, and the 1A of charge current. The pulsing stops when the lower portion of the charger voltage exceeds 4.200V ±1% or the timer ends the charge cycle. 7. After the timer has timed out, slowly decrease the age rises much slower than the battery simulator, resulting in a very gradual decrease in pulse duty cycle. When the duty cycle drops to 10%, the CHRG LED goes off, though there is still 40µA flowing through the LED. battery simulator power supply. At approximately 4.05V the charge current resumes and a new charge cycle begins. This is the Recharge Threshold Voltage. When the timer ends (3 hours for a 0.1µF timing capacitor) the charge cycle ends and the CHRG pin becomes high impedance. Connecting a new battery or cycling the input power turns on the CHRG LED, starting a new charge cycle. A new charge cycle also begins if the battery voltage drops below 4.05V, though the CHRG LED is not on. creased from the programmed 3 hours to approximately 30 seconds by reducing the timer capacitor (C4) from 0.1µF to 270pF When the charger is in the pulse mode, the DVM reading appears to exceed the 4.2V Li-Ion float voltage. This is because when the charger is pulsing, the LTC4052 monitors the charger’s output voltage when the charge current is not flowing. Because of the battery and pack protection ESR, wiring and connector resistance, the charger’s output voltage will exceed the 4.2V float voltage when the charge current is flowing. Figure 2 shows typical waveforms when the battery is near the end of the charge cycle. The charger output voltage, when charge current is flowing, approaches NOTE: For evaluation purposes, the time can be de- 8. To verify battery drain current, remove the input sup- ply voltage. The ammeter that was reading charge current now reads the battery drain current. A typical value is less than 1µA. 9. To verify the overcurrent protection feature, adjust the battery simulator power supply to approximately 3.5V. Increase the current limit of the input power supply to approximately 2.5A. When the charge current reaches the overcurrent threshold of approximately 1.9A, the charge current immediately stops, waits for 640ms, then rises again, resulting in short pulses of current at approximately 1.6Hz. These short pulses of current represent an average current of approximately 1% of the overcurrent level of 1.9A. Figure 3 shows the waveforms. 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 531 LI-ION BATTERY CHARGER MEASURE CHARGE CURRENT (IBAT) + + + VBAT + – INPUT POWER SUPPLY 4.5V–10V 2.5A WITH ADJUSTABLE CURRENT LIMIT – RECOMMENDED LI-ION BATTERY SIMULATOR* + 2Ω 10W PRELOAD – – BATTERY SIMULATOR BENCH POWER SUPPLY 0V–4.3V 2A WITH COURSE AND FINE VOLTAGE ADJUSTMENT – * CAN USE A LI-ION BATTERY, THOUGH TESTING TAKES MORE TIME Figure 1. Proper Measurement Equipment Setup NOTE: Although it would take more time, this charger can also be evaluated using a rechargeable Li-Ion battery in place of the battery simulator pictured here. If you use an actual battery, keep the DC resistance between the charger and the battery to a minimum, as this will affect the charge current in the constant voltage mode. 6V INPUT VOLTAGE 5V 4V THIS AMPLITUDE IS A RESULT OF THE TOTAL ESR AND 1A OF CHARGE CURRENT 4.25V CHARGER OUTPUT VOLTAGE 4.20V 4.15V TOTAL ESR = 60mΩ AC ADAPTER = 5.8V AC ADAPTER CURRENT LIMIT = 1A 1.0A CHARGE CURRENT 0.5A 0A Figure 2. End of Charging Cycle 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 531 LI-ION BATTERY CHARGER 6V INPUT VOLTAGE 5V 4V 4.25V CHARGER OUTPUT VOLTAGE 4.20V 4.15V 1.0A CHARGE CURRENT 0.5A 0A Figure 3. Overcurrent Protection 4 5 4 3 2 1 D D VIN +VIN 4.5V-10V 1A Limit E1 D2 GRN ACPR D1 RED CHRG R2 750 R1 750 R4 10K U1* 3 LTC4052EMS8E C1 0.047uF 25V +VIN C2 0.022uF 25V CHRG C 2 ACPR GND C3 1.0uF 16V 7 GATE 6 R5 4.7 R3 0.04 1206 SENSE 1 BAT 8 C E3 BAT TIMER 4 5 GND E2 Single Li-lon Cell C4 0.1uF 16V GND E4 B B CONTRACT NO. * VERSION TABLE A VERSION Battery Voltages DC531A-A 4.2V APPROVALS DRAWN U1 LTC4052EMS8E-4.2 June Wu DATE 5/3/02 CHECKED TECHNOLOGY TITLE DESIGNER 5/3/02 SIZE CAGE CODE Thursday, February 20, 2003 SCALE: 4 A LTC4052EMS8E, Li-Ion Battery Pulse Charger APPROVED ENGINEER Fran Hoffart 5 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 3 DWG NO FILENAME: 2 REV DC531A SHEET A 1 1 OF 1