Battery Voltage Battery Voltage Quick Start Manual For Linear Technology Demo Board DC384A LTC1730 Pulse Charger Demonstration board DC384A is complete Current Limited pulse battery charger designed to charge AC Adapter LTC1730 5V to 9V one 4.1V or 4.2V Lithium-Ion cell (Float voltage can be selected using jumpers on the Li-Ion + 1 Amp 1A demo board). The charge current is Cell determined by the current limit of the input 4.20V power supply (AC wall adapter) Please see the LTC1730 Data Sheet for additional information.. Figure 1. Basic LTC1730 Charger Concept THE INPUT SUPPLY TO THIS DEMO BOARD MUST HAVE CURRENT LIMITING. THE CURRENT LIMIT DETERMINES THE CHARGE CURRENT. The LTC1730 includes an overcurrent protection feature which 1.5A will protect itself and the battery from excessive current in the event that an AC wall adapter is used that has the incorrect 1.0A current limit, or no current limit. If the adapter current exceeds 0.5A 1.5A, the charger s internal switch immediately turns off, and will Charge Current 0 4.220V turn on again after several hundred milliseconds. If the high Battery Voltage current is still present, this condiion will continue. The average 4.200V charge current in this condition is very low. See Figure 2. 6V 4.180V At the begining of a typical charge cycle, if the battery voltage is 4V Input Voltage less than 2.45V, a trickle current of 35mA will slowly bring the 2V battery up to an acceptable voltage to start the full current 0 portion of the charge cycle. Once the battery exceeds 2.45V the internal switch turns on and passes the full constant current of Figure 2. Waveforms showing the wall adapter into the battery. overcurrent protection As the battery continues to charge, the battery voltage rises. When it is approximately 30mV below the programmed float 1.5A voltage of 4.1V or 4.2V, the internal switch begins to cycle off and on. This cycling continues until the battery voltage 1.0A (measured during the portion of the pulsing when no charge 0.5A current is flowing) reaches 4.200V. As the battery voltage Charge Current approaches the 4.2V threshold , the pulsing becomes less and 0 4.250V less frequent, until it finially stops pulsing entirely. The battery is 4.200V now fully charged. Typically, the pulsing will stop before the 3 Battery Voltage 6V 4.150V hour safety timer ends the charge cycle. See Figure 3. 4V Note: Because of the ESR of the battery and associated wiring 2V Input Voltage resistance, the battery voltage will rise when the internal switch is on and the current is flowing into the battery. The LTC1730 0 measures the battery voltage when the charge current is not flowing, and uses this voltage level to determine when to stop Figure 3. Waveforms showing pulsing. Because of this resistance, the voltage at the charger pulsing for a near full output will be greater than the programmed float voltage when charge battery condition the charge current is flowing. Figure 3 shows a 50mV jump in battery voltage with 1A of charge current flowing, which matches exactly with the 50m of DC resistance measured in the battery and associated wiring. To evaluate this demoboard, connect a 5 to 8 Volt, 1A current limited power source to the +VIN and GND terminals of Demoboard DC384A. Connect a 4.1 or 4.2V discharged Li-Ion battery to the BAT and GND terminals. (Select the appropriate jumper location for JP1). Minimize the DC resistance between the charger output and the battery. The full output current of the power source will flow into the battery for approximately 30 to 60 minutes (depending on the capacity of the battery) and then will begin pulsing until the battery voltage reaches the programmed float voltage, or the 3 hour timer ends the charge. 7/31/02 Charge Current Charge Current Input Voltage Input VoltageBattery Simulator To Test Charger Operation Without Having to Charge and Discharge a Battery, Use the following setup tor for testing the Battery Charger Demo Board. The battery simulator will will source and sink current, similar to an actual battery. Any level of charge from fully discharged to fully charged can be quickly simulated by simp ly changing the battery simulator power supply voltage. A fully discharged Li-Ion cell will be approx. 2.6V and a fully charged cell will be either 4.1V or 4.2V depending on the battery chemistry. When the cell is nearly fully charged, small changes in battery voltage will result in large changes in charge current . Measure Charge Current Current Sense Resistor Volt For a pulse charger, Li-Ion Battery Simulator Meter the power supply must have current limiting Battery Simulator Input Bench Power Supply 0.1 Power Supply 5V +V BAT + + IN 2.2V to 4.3V 2.5 Ohm Battery Charger 2.5A 10W Demo Board Preload GND - - GND 4.8V to 5.2V Course Fine 1A Voltage Adjust Volt Meter Measure Battery Voltage When testing switch mode chargers, use lower value current sense resistors to minimize the output ripple voltage. To determine the preload resistor value use Ohms law, R = E / I, with the following information where E is the fully discharged battery voltage, and I is the maximum charge current + 10%. To determine the maximum current required for the Battery Simulator Power Supply use Ohms law, I = E / R, where E = the maximum battery voltage, and R is the preload resistor value.