QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 558A 3-PHASE HIGH EFFICIENCY DC/DC CONVERTER LTC3731CUH DESCRIPTION Demonstration circuit 558 is a high current step-down components are used and the power components is TM 2 PolyPhase converter featuring the LTC3731 three- within a 0.8 x 2.3 inch footprint area. phase synchronous buck controller. The demo circuit input voltage is from 5V to 14V and output is 1.5V/60A. Design files for this circuit board are available. Call To minimize the supply footprint size and improve the the LTC factory. thermal performance, the 5mm x 5mm QFN package LTC3731CUH controller is used. High density power Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Minimum Input Voltage 5V Maximum Input Voltage 14V V I = 0A to 60A 1.5V1% OUT OUT Maximum Continuous Load Current Without heat sink, without cooling fan 50A o (DT =50 C) Without heat sink, with cooling fan (300LFM) 60A MAX With heat sink, with cooling fan (300LFM) 70A Nominal Switching Frequency Set by resistor divider on demo boards 400kHz Typical Efficiency V = 12V, V = 1.5V, I = 60A, using external +5V for IC 82.4% IN OUT OUT bias QUICK START PROCEDURE Demonstration circuit 558 is easy to set up to evaluate 3. Connect the electronic load to Vout+ and Vout-. Pre- the performance of the LTC3731CUH. Refer to Figure 1 set the load current to be 0A. for proper measurement equipment setup and follow the 4. Turn on the power at the input. procedure below: 5. Check for the proper output voltages at no load and full load. Vout = 1.485V to 1.515V. Cooling fan is 1. Preset the following jumpers on the demo board: needed if the load current is higher than 50A. FCB-CCM, FREQ-INT PROG, 5V SEL-INT, DLC BIAS- 6. Adjust the loads and input voltage within the operat- OFF and DLC-OFF. With above jumpers setup, the ing range and observe the output voltage regulation, supply is running at about 400kHz phase frequency, efficiency and other parameters. and using the on board +5V bias supply. 7. (Optional) DC558A board has optional +5V bias input 2. Preset the voltage of the input power supply to be pins for better efficiency at 12V supply input voltage. 12V. Preset the current limit of input power supply to To use the external 5V bias voltage, set jumper 5V be large than 25A. With power off, connect the input SEL-EXT. Apply the supply input voltage before apply- power supply to Vin and GND. ing the +5V bias voltage. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 558A 3-PHASE HIGH EFFICIENCY DC/DC CONVERTER 8. (Optional) To perform the load transient test, set puts to oscilloscope inputs. Adjust R34 and R38 for jumpers DLC BIAS-ON and DLC-ON. Use coaxial ca- desired load current step and rising slope. Adjust R33 bles to connect LOAD STEP and Vout+ coaxial out- for desired load current falling slope. Optional +5V Bias Supply Figure 1. Proper Measurement Equipment Setup 2 VVoouutt VVV Iin V Current Shunt Current Shunt Load VV VV 60A Vin Iout Vin