QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1020 HIGH EFFICIENCY USB POWER MANAGER + TRIPLE STEP-DOWN DC/DC LTC3555 DESCRIPTION Demonstration Circuit 1020 is a High Efficiency all of the 2.5W available from the USB port to the USB Power Manager + Three Step-Down DC/DC system load with minimal power wasted as heat. This feature allows the LTC3555 to provide more Converters featuring the LTC3555. The power to the application and eases the constraint of LTC3555 is a highly integrated power manage- thermal budgeting in small spaces. Two of the three ment and battery charger IC for Li-Ion/polymer bat- general purpose switching regulators can provide up tery applications. It includes a high efficiency cur- to 400mA and the third can deliver 1A. The entire rent limited switching PowerPath manager with product can be started from an external push button automatic load prioritization, a battery charger, an 2 and subsequently controlled via I C. The LTC3555 ideal diode and three general purpose synchronous is available in the 28-pin (4mm 5mm 0.75mm) step-down switching regulators. Designed specifi- QFN surface mount package. cally for USB applications, the LTC3555s switch- Design files for this circuit board are available. Call ing power manager automatically limits input cur- the LTC factory. rent to a maximum of either 100mA or 500mA for , LTC and LT are registered trademarks of Linear Technology Corporation. USB applications or 1A for AC-powered applica- PowerPath is a trademark of Liner Technology Corporation. tions. Unlike linear PowerPath controllers, the LTC3555s switching input stage transmits nearly TABLE 1. TYPICAL SPECIFICATIONS (25C) Input Voltage Range VBUS 4.35V to 5.5V VOUT 3.4V to 4.7V (Mode and load dependent) LDO3V3 3.3V (Load and VOUT dependent) Output Float Voltage VBAT (constant voltage mode) 4.2V Output Charge Current IBAT (constant current mode) 0.5A, (RPROG = 2.00K) VOUT1 3.3V, 400mA VOUT2 3.0V-1.6V, 400mA VOUT3 1.5V-0.8V, 1A QUICK START PROCEDURE Demo Circuit 1020 is best evaluated using a Li-Ion Complete the Quick Start Procedure outlined in or Li-Polymer battery. When using a battery simu- the Quick Start Guide for Demo Circuit 590 avail- lator for evaluation, oscillations must be verified able from the Linear Technology Web Site, prior with a real battery at the same conditions because to proceeding. it is difficult to match the impedance of a real bat- Refer to Figure 2 for the proper measurement tery. Capacitor C15 was added to simulate the low equipment setup and jumper settings and follow impedance of a real battery. It will allow proper the procedure below. NOTE: When measuring the input or output voltage ripple, operation of the demo circuit with or without a care must be taken to avoid a long ground lead on the oscil- battery and even with a battery simulator consist- loscope probe. Measure the input or output voltage ripple by ing of a power supply in parallel with a 3.6 Ohm touching the probe tip directly across the VBUS or VOUT(x) resistor. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1020 HIGH EFFICIENCY USB POWER MANAGER + TRIPLE STEP-DOWN DC/DC LTC3555 and GND terminals. See Figure 3 for proper scope probe tor between the J2-3 terminal and the GND technique. terminal. Then set the NTC jumper to EXT. 1. After following the software installation pro- 4. Set JP2 and JP3 (ILIM0 and ILIM1 respec- cedure in the DC590 Quick Start Guide, con- tively) to LO. At Power-up, the average in- nect the DC1020, the DC590 and the Host PC put current setting will be equal to the value set as shown in Figure 1. The following demon- 2 by the position of JP2 and JP3 until an I C stration software should pop-up as soon as the command is received and over-writes that de- DC1020 board is connected to the Host PC. fault value. TABLE 2. Input Current Limit Settings ILIM1 ILIM0 CURRENT LIMIT 0 0 100mA (1X) 0 1 1A (10X) 1 0 0.5mA (SUSP) 1 1 500mA (5X) 5. Connect a 0 to 25mA adjustable load in series with an ammeter between the LDO3V3 and GND terminals. Connect a voltmeter between the LDO3V3 and GND terminals. 6. Connect a 0 to 2A adjustable load in series with an ammeter between the VOUT terminal and the GND terminal. Connect a voltmeter between the VOUT and GND terminals. 7. Connect a 0 to 400mA adjustable load in series FIGURE 1: Graphical User Interface Demon- stration Software for DC1020. with an ammeter between the VOUT1 and GND terminals. Connect a voltmeter between 2. If using an external supply, connect a 0 to 6V, the VOUT1 and GND terminals. 1.5A supply with voltage adjusted to 0V be- 8. Connect a 0 to 400mA adjustable load in series tween the VBUS and GND terminals. Connect with an ammeter between the VOUT2 and a voltmeter across the VBUS and GND termi- GND terminals. Connect a voltmeter between nals. If using the USB input option, have cable the VOUT2 and GND terminals. ready to plug in for when all loads and jumpers 9. Connect a 0 to 1.0A adjustable load in series are set. Connect the positive terminal of a with an ammeter between the VOUT3 and voltmeter to CLPROG and the negative termi- GND terminals. Connect a voltmeter between nal to GND to measure the average input cur- the VOUT3 and GND terminals. rent. The voltage on CLPROG will reach 1.188 10. Connect a Li-Ion or Li-Polymer battery with Volts when the average input current limit is the positive lead to the BAT terminal and the reached. Do not use the USB input and an negative lead to a GND terminal. Connect the external supply at the same time. positive lead of a voltmeter to the BAT termi- 3. Set JP1, NTC jumper to INT to use the demo nal and the negative lead to the GND terminal. board resistor network. To use an external Connect the positive terminal of a voltmeter to NTC resistor, connect the external NTC resis- PROG and the negative terminal to GND to measure the current flowing into the battery. 2