QUICK START GUIDE FOR DC1550A LTC3553EPD: Micropower USB Power Manager with Li-Ion Charger, Buck DC/DC, and LDO Regulator DESCRIPTION Demonstration Circuit DC1550A is a Micropower USB Power Manager with Li-Ion Charger, Buck DC/DC, and LDO Regulator featuring the LTC 3553. PERFORMANCE SUMMARY Specifications are at T = 25C A SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VBUS Bus Input Voltage Range 4.35 6 V V(BAT) Battery Float Voltage Constant Voltage Mode 4.15 4.23 V I(BAT) Battery Charge Current Constant Current Mode, R = 1.87k 420 500 mA PROG VLDO LDO Output Voltage I(VLDO) 200mA 3.25 3.35 V VBUCK Buck Regulator Output Voltage I(VBUCK) 200mA 1.15 1.25 V QUICK START PROCEDURE Refer to Figure 1 for the proper measurement The LTC3553 is now operating in normal mode equipment setup and jumper settings and follow the drawing more current from the battery. However procedure below. the regulators are now capable of delivering over NOTE. When measuring the input or output voltage ripple, care 200mA each. Also, since VBUS is now available, must be taken to avoid a long ground lead on the oscilloscope the battery charger is operating, but charge cur- probe. Measure the input or output voltage ripple by touching the probe tip directly across the VBUS or VOUT(x) and GND terminals. rent is limited by the input current limit to See Figure 2 for proper scope probe technique. 100mA. 3. Set HPWR (JP2) to 500mA. Observe I(VBUS) 1. Set PS1 = 0V, PS2 = 3.6V. Press ON button (AM1), I(BAT) (AM2) and VPROG (VM2). for > 0.5s. Observe I(BAT) (AM2), VBUCK The input current limit is now 500mA, so the bat- (VM5) and VLDO (VM6). tery charger is delivering ~420mA to the battery. The LTC3553 is in STBY which reduces the bat- 4. Set LD2 to 200mA, LD3 to 200mA. Observe tery current to less than 15A, even with both VBUCK (VM5), VLDO (VM6) and I(BAT) (AM2). regulators running. In STBY the maximum cur- Each regulator is supplying 200mA, and since rent from regulators is reduced to as low as the efficiency is ~90%, drawing ~225mA. So, 10mA the battery charger is only delivering approxi- 2. Set STBY (JP6) to OFF, PS1 to 5V. Observe mately 50mA. This is because the input current I(VBUS) (AM1), I(BAT) (AM2) and VPROG limit is 500mA 225mA 225mA = 50mA. (VM2). 1 LTC3553EPD 5. Set LD2 to 0A, LD3 to 0A. Press OFF button. Observe VBUCK (VM5) and VLDO (VM6). The regulators are now off and therefore supply- ing 0 current. The battery charger is once again supplying ~ 420mA to the battery. 6. Reset the Jumpers to their default position. 2