DEMO CIRCUIT 1468A QUICK START GUIDE LTC3554EPD Micropower USB Power Manager with Two Step-Down Regulators DESCRIPTION Demonstration Circuit DC1468A is a Micropower USB Power Manager with Two Step-Down Regulators featuring the LTC 3554. 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 VOUT1 Output Voltage 1 I(VOUT1) 200mA 3.25 3.35 V VOUT2 Output Voltage 2 I(VOUT2) 200mA 1.15 1.25 V QUICK START PROCEDURE Refer to Figure 1 for the proper measurement 2. Set STBY (JP4) to OFF, PS1 to 5V. Observe equipment setup and jumper settings and follow the I(VBUS) (AM1), I(BAT) (AM2) and VPROG procedure below. (VM2). The STBY jumper is off, and the battery NOTE. When measuring the input or output voltage ripple, care charger is trying to charge the battery at 500mA, must be taken to avoid a long ground lead on the oscilloscope but the input current limit is keeping the charge probe. Measure the input or output voltage ripple by touching the probe tip directly across the VBUS or VOUT(x) and GND terminals. current at 100mA. See Figure 2 for proper scope probe technique. 3. Set HPWR (JP2) to 500mA. Observe I(VBUS) (AM1), I(BAT) (AM2) and VPROG (VM2). The 1. Set PS1 = 0V, PS2 = 3.6V. Press ON button input current limit is now 500mA, so the battery for > 0.5s. Observe I(BAT) (AM2), VOUT1 (VM5) charger is charging at 450mA, and the buck and VOUT2 (VM6). The regulator ENable lines regulators are unloaded. are low. Pressing the ON button turns on the 4. Set LD2 to 200mA, LD3 to 200mA. Observe regulators for 5s, via the pushbutton controller. VOUT1(VM5), VOUT2 (VM6) and I(BAT) (AM2). The regulator ENables are bootstrapped to the The buck regulators are each loaded at 200mA. outputs of the regulators, so regulators stay on These loads are reflected back to the VBUS input indefinitely. The STBY jumper is on, so the by the ratio of their output voltage to the VOUT LTC3554 draws only ~10A from the battery. Voltage. The buck regulators are higher priority 1LTC3554EPD than the battery charger, so the charger is only charging at the input current limit of 500mA mi- nus the reflected buck regulator loads, ~200mA. 5. Set LD2 to 0A, LD3 to 0A. Press OFF button. Observe VOUT1 (VM5) and VOUT2 (VM6). The OFF button momentarily brings the ENable lines low, shutting regulators off. The battery charge current should now return to 450mA. 6. Reset the Jumpers to their default position. 2