QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1289 NO RSENSE STEP-DOWN DC/DC CONVERTER LTC3879EUD DESCRIPTION Demonstration circuit 1289 is a no rsense step-down The fixed on-time valley current mode architecture of the dc/dc converter featuring the LTC3879EUD. Its output LTC3879EUD provides a very fast load step response. supplies 1.2V 15A and its input voltage range is from Other features of the board include a RUN pin, a TRACK 4.5V to 14V. The demo board uses a high density, two pin, a PGOOD pin and a MODE jumper to select either sided drop-in layout. The power components, excluding CCM or DCM operation at light load. the bulk output capacitors and bulk input capacitors, fit Design files for this circuit board are available. Call within a 0.94 x 0.69 area on the top layer. The control the LTC factory. circuit on the bottom layer has a footprint of 0.40 x 0.50. Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Minimum Input Voltage 4.5V Maximum Input Voltage 14V Output Voltage V V = 4.5V to 14V, I = 0A to 15A 1.2V 2% OUT IN OUT Maximum Output Current 15A Typical Output Voltage Ripple V = 12V, I = 15A (20MHz BW) 18mV IN OUT PP Nominal Switching Frequency 100% load 430kHz Efficiency (see Figure 3 for efficiency curves) V = 12V, 100% load 87.7% Typical IN QUICK START PROCEDURE Demonstration circuit 1289 is easy to set up to evaluate 1. Place jumpers in the following positions: the performance of the LTC3879EUD. Refer to Figure 1 RUN ON for proper measurement equipment setup and follow the MODE CCM procedure below: 2. With power off, connect the input power supply to Vin NOTE: When measuring the input or output voltage rip- and GND. ple, care must be taken to avoid a long ground lead on the oscilloscope probe. See Figure 2 for proper scope 3. Turn on the power at the input. probe technique. Short, stiff leads should be soldered to 4. Check for the proper output voltages. the (+) and (-) terminals of an output capacitor. The Vout = 1.176V to 1.224V probes ground ring needs to touch the (-) lead and the probe tip needs to touch the (+) lead. 5. Once the proper output voltages are established, ad- just 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 1289 NO RSENSE STEP-DOWN DC/DC CONVERTER Figure 1. Proper Measurement Equipment Setup + - COUT VOUT GND Figure 2. Measuring Output Voltage Ripple 2