QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A USB POWER SOLUTION IN DFN 3X4 LTC4085 DESCRIPTION Demonstration circuit DC937A is a complete power controller for a USB powered device. It is based on the LTC4085 and provides the following functions: 700mA CC/CV timer terminated temperature qualified charger suitable for Li-Ion cells, a USB power manager that insures compliance with the USB power specification and power path management for the battery. The LTC4085 uses the intermediate bus voltage topology that results in faster charging and lower power loss than the charger fed topology. All this functionality consumes less than 2 56mm of PCB area. Design files for this circuit board are available. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. Table 1. Performance Summary PARAMETER CONDITION VALUE Input Voltage 4.5V - 5.5V Battery Charger Iout VIN = 5V, Vbat=3.6V 700mA +/- 7% Float Voltage Vin = 5V, battery disconnected from BATT pin 4.20V+/- 35mV Trickle Charge Threshold VIN = 5V 2.9V +/-0.1V Recharge Threshold VIN = 5V (Vfloat – 130mV) to (Vfloat-60mV) Input Current 500mA Mode VIN = 5V, USB Active 500mA Mode 475mA typical, 500mA max Input Current 100mA Mode VIN = 5V, USB Active 100mA Mode 93mA typical, 100mA max Input Current Suspend Mode VIN =5V, USB Suspend 300uA max USB Current OPERATING PRINCIPLES DC937A is the demo board for LTC4085. This chip manages the power supplies that would be typical for a USB powered device. Power is input from either the USB cable or an adapter to an intermediate voltage bus. The intermediate voltage bus is preferentially powered from the adapter, then USB and finally if required from the battery via an ideal diode. The battery charger is a CC/CV timer terminated type capable of charge currents of up to 1500mA. QUICK START PROCEDURE Demonstration circuit DC937A is easy to set up to evaluate the performance of the LTC4085. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. Connect input power supply, meters and output load as shown in Figure 1. USB Charging 2. Place the USB ON/OFF jumper (JP1) in the ON position. Place the USB current jumper (JP2) in the 500mA position. Set the battery simulator voltage to zero, slowly raise the USB input voltage. When the supply voltage exceeds 3.8V the charger should activate and the charge LED D2 will illuminate. The battery will be in trickle charge mode, IBAT is around 70mA. Increase the battery voltage to about 2.9V. The 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A USB POWER SOLUTION IN DFN 3X4 battery charge current (IBAT) will increase to 475mA. Note that the input current from the USB (IUSB) does not exceed the USB spec of 500mA. 3. 4. 5. Now increase the load on the SYSTEM LOAD OUTPUT (IOUT). Note that as the output load is increased the charging current is decreased and the USB current remains within the 500mA limit. Place the USB current jumper in the 100mA position and note that USB input current falls to maintain compliance with the USB input current spec. Also note that as the external load is increased the battery will start to discharge into the SYSTEM LOAD OUTPUT, illustrating the ideal diode function of the LTC4085 Place the USB ON/OFF jumper (JP1) in the OFF position and note that the USB current falls to under 300uA to comply with the USB suspend mode current. Adapter Charging 6. Ramp up the wall adapter voltage. When the wall adapter exceeds 4.3 volts the LTC4085 will cease drawing current from the USB and switch over to the wall adapter. Both the AC-present LED (D1, red) and charge LED (D2, green) are on. 7. Note that the charge current to the battery has increased to 700mA. 8. Increase the battery voltage to 4.2V and note that the charge current falls to 0. This illustrates the constant voltage portion of the charging characteristic. In the mean time, the charge LED (D2) turns off. Battery Powered Operation 9. Set Both USB input voltage and the adapter input voltage to zero. The battery will now power the load on the System Load Output, illustrating the ideal diode function of the LTC4085. Note that the battery is now being discharged. Other Frequency at charge timer cap C3 changes with charging current, indicating the adaptive feature to ensure the full charge of battery. 10. Pins are provided to all control functions in order to simplify wiring of the demo circuit into a system board. 11. NTC function; provision has been made for connection of an external 10k NTC, for temperature qualified charging. To use this feature set the NTC jumper in the external position and connect the external NTC to the NTC terminal and ground. 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A USB POWER SOLUTION IN DFN 3X4 Figure 1. Proper Measurement Equipment Setup 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC937A USB POWER SOLUTION IN DFN 3X4 4