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