DEMO CIRCUIT 1345 QUICK START GUIDE WIDE INPUT VOLTAGE RANGE NO RSENSE STEP-DOWN DC/DC CONVERTER LTC3879EMSE DESCRIPTION Demonstration circuit 1345 is a wide input voltage range, no Rsense step-down dc/dc converter featuring the LTC3879EMSE. Its output voltage is 1.2V with a load rating of 12A and the input voltage range is 4.5V to 34V. The fixed on-time valley current mode architecture of the LTC3879EMSE provides a very fast load step response. Other features of the board include a RUN pin, a TRACK pin, a PGOOD pin and a MODE jumper to select either CCM or DCM operation at light load. Design files for this circuit board are available. Call the LTC factory. Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE Minimum Input Voltage 4.5V Maximum Input Voltage 34V Output Voltage VOUT VIN = 4.5V to 34V, IOUT = 0A to 12A 1.2V ±2% Maximum Output Current 12A Typical Output Voltage Ripple VIN = 12V, IOUT = 12A (20MHz BW) 20mVP–P Nominal Switching Frequency VIN = 12V, IOUT = 12A 300kHz Efficiency (see Figure 3 for efficiency curves) VIN = 12V, IOUT = 12A 90% Typical QUICK START PROCEDURE Demonstration circuit 1345 is easy to set up to evaluate the performance of the LTC3879EMSE. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. Place jumpers in the following positions: NOTE: When measuring the output voltage ripple, care 2. With power off, connect the input power supply to must be taken to avoid a long ground lead on the oscilloscope probe. See Figure 2 for proper scope probe technique. Short, stiff leads should 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. RUN ON MODE CCM Vin and GND. 3. Turn on the power at the input. 4. Check for the proper output voltages. Vout = 1.176V to 1.224V 5. Once the proper output voltages are established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 1 DEMO CIRCUIT 1345 QUICK START GUIDE Vin V A A Iin Iout Vin supply Load V Vout Figure 1. Proper Measurement Equipment Setup + COUT VOUT - GND Figure 2. Measuring Output Voltage Ripple 2 DEMO CIRCUIT 1345 QUICK START GUIDE Fsw = 300kHz, CCM 95 Vin=5V Vin=12V 90 Vin=24V Vin=34V Efficiency 85 80 75 Parameters: QT = Infineon BSC093N04LSG QB = Infineon BSC035N04LSG L = Wurth 744325072 0.72uH, DCR=1.3mΩ +/- 10% Ron = 576kΩ 70 65 60 0 2 4 6 8 10 12 14 Load current (Amps) Figure 3. Typical Efficiency Curves 3 DEMO CIRCUIT 1345 QUICK START GUIDE 4