DC867A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC867 DUAL INPUT USB / AC ADAPTER STANDALONE LI-ION CHARGER LTC4075XEDD DESCRIPTION Demonstration circuit DC867 features the to be floating or pulled low to enable AC adapter LTC4075X standalone linear charger that is capa- mode charging. ble of charging a single-cell Li-Ion battery from There are two LED indicators (the third LED is for both AC adapter and USB inputs. DC867 is de- optional USB power indication) for battery signed to demonstrate the LTC4075X capability to charge status and input power status. The automatically select the appropriate power source CHRG LED will be turned on when LTC4075X is for charging. DC867 is set up so that when the charging and it will be turned off when charging is USB source is used as the input, the charge cur- terminated or the LTC4075X is disabled. The rent is set to 500mA and when the AC adapter is PWR LED will be turned on when the input available, regardless of the USB input connection, source is sufficient to begin charging. The PWR the charge current increases to 800mA. LED will be turned off when the input source is not The enable operation of the LTC4075X changes present or the input source is below the under with different input sources. When the LTC4075X voltage lockout threshold (Typically 4.2V for AC is charging from the AC adapter source, a logic adapter and 4V for USB inputs). low enables the charger and when the USB input The charge currents for both USB and AC adapter is used for charging, logic high is needed to acti- charging modes and termination current setting vate the LTC4075X. DC867 is design to start can be easily adjusted by changing the program charging with AC adapter as default mode. For resistors. Please refer to the LTC4075X datasheet USB input charging, the JP1 jumper has to be set for more information. to the USB on position or the USB ENABLE pin Design files for this circuit board are available. (turret) has to be pulled above 1V. The jumper Call the LTC factory. setting can be USB on for AC adapter charging mode but the USB ENABLE terminal (turret) has LTC is a trademark of Linear Technology Corporation Table 1. Performance Summary (T = 25C unless otherwise noted) A PARAMETER FOR LED DRIVER CONDITION VALUE Input Voltage Range AC adapter and USB 4.3V to 6V Output Float Voltage VBAT (constant voltage mode) Over The Full Operating Temperature 4.2V +/- 1% Range (0C to 85C) Charge Current AC adapter R4 = 1.24K 800mA Charge Current USB Input R3 = 2.10K 476mA (500mA max, 0C to 85C) Charge Termination R5 = 2.00K 50mA 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC867 DUAL INPUT USB / AC ADAPTER STANDALONE LI-ION CHARGER QUICK START PROCEDURE stant voltage portion of the charging character- Demonstration circuit 867 is easy to set up to istic. evaluate the performance of the LTC4075X. Refer to Figure 1 for proper measurement equipment 4. Set both power supply and battery simulator setup and follow the procedure below: back to 0V and connect the power supply (or USB source) to USB INPUT and GND termi- The charger can be evaluated using an actual nals and LI-ION+ and GND terminals as Lithium Ion battery or a battery simulator. The bat- shown in Figure 1 to test the USB charging tery simulator is faster because all battery state-of- mode. Make sure that the USB ENABLE charge conditions can be quickly simulated. jumper is set to USB ON position for ena- bling USB input charging mode. A battery simulator consists of an adjustable power supply with a load resistor across the power 5. Increase the battery voltage to 3.6V. Observe supply output. The resistor value is selected that the 476mA battery charge current (measured will provide approximately 1A when the power at input). Start to increase the USB input volt- supply is set for 2.5V and power supply must pro- age. When the input supply voltage exceeds vide at least 1.7A when adjusted for 4.2V. An ex- 4V the charger should activate and the CHRG ample for battery simulator would be a 2 Ohm, 10 LED will illuminate. Watt power resistor connected to the output of a 6. Test the USB shutdown mode by placing the 5V, 5A bench supply. USB ENABLE jumper to USB OFF position. 1. With the input power supply and battery simu- Note that the input current (or USB current) lator power supply adjusted to 0V, connect the falls to under 30uA to comply with the USB two power supply outputs to the ADAPTER shutdown mode. INPUT and GND terminals and LI-ION+ and 7. Place jumper back to USB ON position for GND terminals as shown in Figure 1 to test AC enabling USB charging. Increase the battery adapter charging mode. Make sure that USB voltage to 4.2V and note that the charge cur- ENABLE terminal (turret) is floating or pulled rent falls to 0 and CHRG LED will be turned low for enabling AC adapter mode charging. off. This illustrates the constant voltage portion 2. Increase the battery voltage to 3.6V. Observe of the charging characteristic. Note that the the 800mA battery charge current (measured input current (or USB current) decrease down at input). Start to increase the adapter input to 50uA, which is the typical USB current un- voltage. When the input supply voltage ex- der standby mode (when the charging is termi- ceeds 4.2V, the charger should activate and nated). the PWR and CHRG LEDs will illuminate. 3. Increase the battery voltage to 4.2V and note that the charge current falls to 0 and CHRG LED will be turned off. This illustrates the con- 2