QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 506 500MA SPREAD-SPECTRUM, LOW NOISE, INDUCTORLESS STEP DOWN DC/DC CONVERTER LTC3251EMSE DESCRIPTION Demonstration circuit 506A is a two-phase, a low external parts count and requires only step down charge pump DC/DC converter four small surface mount capacitors. DC 506 featuring the LTC3251EMSE. It produces regu- demonstrates appropriate layout techniques lated 1.5V output voltage at up to 500mA of for the LTC3251 Inductorless DC-DC converter. output current from 3.2V to 5.5V input. A This power supply circuit is ideally suited for unique two phase, spread spectrum architec- space-constrained battery-powered applica- ture of the LTC3251 provides highly efficient tions that require small size and low operating and low noise operation. The burst and super- current. burst operating modes also reduce operating Design files for this circuit board are available. current at light load conditions. The circuit has Call the LTC factory. QUICK START PROCEDURE Demonstration circuit DC506 is easy to set up 5. Check for the proper output voltages. VOUT to evaluate the performance of the LTC3251. = 1.5V. Refer to Figure 1 for proper measurement If there is no output, temporarily disconnect equipment setup and follow the procedure the load to make sure that the load is not below: set too high. NOTE: When measuring the input or output 6. Once the proper output voltages are voltage ripple, care must be taken to avoid a established, adjust the loads up to 500mA long ground lead on the oscilloscope probe. and observe the output voltage regulation, Measure the input or output voltage ripple by input and output ripple voltage, efficiency touching the probe tip directly across the VIN and other parameters. or VOUT and GND terminals. See Figure 2 for NOTE: IOUT derates linearly to 200mA for VIN proper scope probe technique. less than 3.5V. 1. With power off, connect input power 7. For continuous mode operation, set opera- source to VIN and GND terminals. Input tion mode selector jumper JP1 in the VIN voltage range is limited to between 3.2V position, JP2 in the GND position. Please re- and 5.5V. fer Table1 for other modes of operation. 2. Place operation mode selector jumper JP1 in the GND position, JP2 in the VIN position Table 1. Modes of Operation: for Burst Mode operation. JP1 JP2 MODE 3. Connect load between the VOUT and GND GND GND SHUTDOWN terminals. GND VIN BURST 4. Turn on the power at the input. VIN GND CONTINUOUS NOTE: Make sure that the input voltage does VIN VIN SUPER BURST not exceed 5.5V. 1 GND VIN QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 506 500MA SPREAD-SPECTRUM, LOW NOISE, INDUCTORLESS STEP DOWN DC/DC CONVERTER + + + LOAD Figure 2. Scope Probe Placement for Figure 1. Proper Measurement Equipment Setup Measuring Input or Output Ripple F Figure 4. Input Ripple Figure 5. 1.5V Output Ripple F (VIN = 3.5V, IOUT = 500mA), 20MHz Bandwidth (VIN = 3.5V, IOUT = 500mA), 20MHz Bandwidth 2 + + +