DEMO CIRCUIT 1450A QUICK START GUIDE LTC3854EDDB SMALL FOOTPRINT BUCK CONVERTER DESCRIPTION Demonstration circuit 1450A is a small foot print, high efficiency synchronous buck converter with 4.5V to 26V input range. It can supply 5A maximum load current at 2.5V output. The demo board features the LTC®3854EDDB controller. The controller features a 400kHz constant frequency current mode architecture. With a wide input range and output range, the LTC3854 is ideal for automotive, telecom, industrial and distributed DC power systems. This board has a compact solution size with dual So-8 MOSFETs, small inductor and capacitor footprints. The package of LTC3854EDDB is a small, low thermal impedance, 12-Lead (3mm x 2mm) plastic DFN. Table 1. The RUN/SS pin (JP1) provides both soft-start and enable features. To shut down the converter, one simple way is to force the RUN pin below 0.4V (JP1: OFF). Design files for this circuit board are available. Call the LTC factory. Performance Summary (TA = 25°C) PARAMETER CONDITION Input Voltage Range VALUE 4.5V to 26V Output Voltage, VOUT VIN = 4.5-26V, IOUT = 0A to 5A 2.5V ±2% Maximum Output Current, IOUT VIN = 4.5-26V, VOUT = 2.5V 5A Typical Efficiency VIN = 15V, VOUT = 2.5V, IOUT = 5A 89.5% Typical Switching Frequency 400kHz 1 LTC3854EDDB QUICK START PROCEDURE Demonstration circuit 1450A is easy to set up to evaluate the performance of the LTC3854EDDB. Refer to Figure 1 for the proper measurement equipment setup and follow the procedure below: 1. With power off, connect the input power supply to Vin (4.5V-26V) and GND (input return). 2. Connect the 2.5V output load between Vout and GND (Initial load: no load). 3. Connect the DVMs to the input and outputs. 4. Turn on the input power supply and check for the proper output voltages. Vout should be 2.5V+/-2%. 5. Once the proper output voltages are established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage and other parameters. Note: When measuring the output or input voltage ripple, do not use the long ground lead on the oscilloscope probe. See Figure 2 for the proper scope probe technique. Short, stiff leads need to be soldered to the (+) and (-) terminals of an output capacitor. The probe’s ground ring needs to touch the (-) lead and the probe tip needs to touch the (+) lead. 2 LTC3854EDDB Figure 1. Proper Measurement Equipment Setup + COUT VOUT - GND Figure 2. Measuring Output Voltage Ripple 3 LTC3854EDDB Figure 3. Efficiency vs load current 4 LTC3854EDDB 5