DC676A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC676 USB POWER SOLUTION IN QFN 4X4 LTC4055 DESCRIPTION Demonstration circuit DC676 is a complete power con- in faster charging and lower power loss than the charger troller for a USB powered device. DC676 is based on the fed topology. All this functionality consumes only 2 LTC4055 and provides the following functions 700mA 100mm of PCB area. CC/CV timer terminated temperature qualified charger suitable for Li-Ion cells, a USB power manager that in- Design files for this circuit board are available. Call sures compliance with the USB power specification and the LTC factory. power path management for the battery. The LTC4055 uses the intermediate bus voltage topology that results Table 1. Performance Summary PARAMETER CONDITION VALUE Input Voltage 4.3-5.5V Battery Charger Iout Vin = 5V, Vbat = 3.6V 700mA +/- 7% Float voltage Vin = 5V 4.20V +/- 1% Trickle Charge threshold V = 5V 2.9V +/- 0.1V IN Recharge threshold Vin 5V Vfloat 60mV Vfloat - 150mV USB Current Input Current 500mA mode Vin = 5V USB Active, 500mA mode 500mA max Input Current 100mA mode Vin = 5V USB Active, 100mA mode 100mA max Input Current suspend mode Vin =5V USB suspend 300uA max OPERATING PRINCIPLES Demo DC676 is based on the LTC4055. This chip man- the adapter, then USB and finally if required from the ages the power supplies that would be typical for a USB battery via an ideal diode. The battery charger is a CC/CV powered device. Power is input from either the USB timer terminated type capable of charge currents of up cable or an adapter to an intermediate voltage bus. The to 800mA and is roughly equivalent to the LTC4053. intermediate voltage bus is preferentially powered from QUICK START PROCEDURE Demonstration circuit DC676 is easy to set up to evalu- 1. Connect input power supply, meters and output load ate the performance of the LTC4055. Refer to Figure 1 as shown in figure 1. for proper measurement equipment setup and follow the USB Charging procedure below: 2. Place the MASTER ON/OFF jumper in the ON position. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC676 USB POWER SOLUTION IN QFN 4X4 3. Place the USB ON/OFF jumper in the ON position. drawing current from the USB and switch over to the Place the USB CURRENT jumper in the 500mA posi- wall adapter. tion. Set the battery simulator voltage to zero, slowly 8. Note that the charge current to the battery has in- raise the USB INPUT voltage. When the supply volt- creased to 700mA. age exceeds 4.3V the charger should activate and the 9. Increase the battery voltage to 4.2V and note that the charge LED will illuminate. The battery will be in charge current falls to 0 this illustrates the constant trickle charge mode. Increase the battery voltage to voltage portion of the charging characteristic. 3.6V. At about 2.9V the battery charge current will in- crease to 485mA. Note that the input current from Battery powered Operation the USB does not exceed the USB spec of 500mA. 10. Set Both USB INPUT voltage and the ADAPTER INPUT 4. Now increase the load on the SYSTEM LOAD voltage to zero. The battery will now power the load OUTPUT. Note that as the output load is increased on the SYSTEM LOAD OUTPUT, illustrating the ideal the charging current is decreased and the USB cur- diode function of the LTC4055. Note that the battery rent remains within the 500mA limit. is now being discharged. 5. Place the USB CURRENT jumper in the 100mA posi- tion and note that USB INPUT current falls to maintain Other compliance with the USB input current spec. Also 11. Pins are provided to all control functions in order to note that as the external load is increased the battery simplify wiring of the demo circuit into a system will start to discharge into the SYSTEM LOAD board. OUTPUT, illustrating the ideal diode function of the LTC4055 12. NTC function provision has been made for connec- tion of an external 10k NTC, for temperature qualified 6. Place the USB ON/OFF jumper in the OFF position and charging. To use this feature set the NTC jumper in note that the USB current falls to under 300uA to the external position and connect the external NTC to comply with the USB suspend mode current. the NTC terminal and ground. Adapter Charging 7. Ramp up the wall adapter voltage. When the wall adapter exceeds 4.3 volts the LTC4055 will cease 2