QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1292 NO RSENSE STEP-DOWN DC/DC CONVERTER LTC3878EGN DESCRIPTION Demonstration circuit 1292 is a NO RSENSE STEPDOWN DC/DC CONVERTER featuring the LTC3878EGN. Its output supplies 1.2V @ 18A and its input voltage range is 4.5V to 14V. The demo board uses a high density, two sided drop-in layout. The power components, excluding the bulk output capacitors and bulk input capacitors, fit within a 0.94” x 0.63” area on the top layer. The control circuit on the bottom layer has a footprint of 0.63” x 0.40”. The fixed on-time valley current mode architecture of the LTC3878EGN provides a very fast load step response. Other features of the board include a RUN/SS pin, a PGOOD pin and jumper to select either CCM or DCM operation at light load. Design files for this circuit board are available. Call the LTC factory. PowerPath is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE Minimum Input Voltage 4.5V Maximum Input Voltage 14V Output Voltage VIN = 4.5V to 14V, IOUT = 0A to 18A Maximum Output Current 1.2V ±2% 18A Typical Output Voltage Ripple VIN = 12V, IOUT = 18A (20MHz BW) 17mVp-p Nominal Switching Frequency 100% load, VIN = 12V, IOUT = 18A 340kHz Efficiency (see Figure 3 for efficiency curves) VIN = 12V, 100% load 88.4% Typical QUICK START PROCEDURE Demonstration circuit 1292 is easy to set up to evaluate the performance of the LTC3878EGN. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE: When measuring the input or output voltage rip- ple, care 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. 1. Place jumpers in the following positions: JP1 RUN ON JP2 MODE CCM 2. With power off, connect the input power supply to Vin and GND. 3. Turn on the power at the input. 4. Check for the proper Vout = 1.176V to 1.224V output voltages. 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 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1292 NO RSENSE STEP-DOWN DC/DC CONVERTER Figure 1. Proper Measurement Equipment Setup + COUT VOUT - GND Figure 2. Measuring Output Voltage Ripple 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1292 NO RSENSE STEP-DOWN DC/DC CONVERTER Fsw = 340kHz, mode = CCM 95 Efficiency 90 85 80 Parameters: Qtop = RJK0305DPB Qbottom = RJK0330DPB L = Pulse PA0515.471NLT Ron = 499K Design optimized for a 12V input 75 70 0 2 4 6 8 10 12 14 16 18 20 Load current (Amps) Vin = 12V Vin = 5V Figure 3. Typical efficiency curves 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1292 NO RSENSE STEP-DOWN DC/DC CONVERTER 4