QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1318 HIGH INPUT VOLTAGE AND HIGH CURRENT DENSITY STEP-DOWN CONVERTER LTC3611EWP DESCRIPTION Demonstration circuit 1318 is a Synchronous StepDown Converter featuring the LTC®3611, the high efficiency, high density DC/DC regulator. The input voltage range of DC1318 is from 9V to 32V and the output voltage is jumper selectable from 1.5V to 3.3V, although LTC®3611 has an input range from 4.5V to 32V and the output voltage range is from 0.6V. The rated load current is 10A. The regulator includes the controller and power MOSFETs in the 9mm by 9 mm QFN package. The constant on time valley mode current control structure delivers very low duty cycle with excellent load transient response. The MOSFET RDS(on) sensing eliminates external sensing resistor and improves supply efficiency. Discontinuous mode operation and continuous mode at light load is also jumper selectable. A forced continuous control reduces noise and RF interference while discontinuous control provides high efficiency at light loads. Design files for this circuit board are available. Call the LTC factory. LTC is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE Minimum Input Voltage 9V Maximum Input Voltage 32V Output Voltage VOUT Jumper selectable (open for 0.6V) 1.5V, 1.8V, 2.5V, 3.3V ± 2% Maximum Continuous Output Current De-rating is necessary for certain VIN, VOUT, and thermal conditions, see datasheet 10ADC Operating Frequency Programmable 500kHz default Efficiency VIN=24V, VOUT =2.5V, IOUT =10A 87.8%, See Figure 3 VIN=24V, VOUT =3.3V, IOUT =10A 89.1%, See Figure 3 VIN=24V, VOUT =1.8V See Figure 5 Load Transient QUICK START PROCEDURE Demonstration circuit 1318 is easy to set up to evaluate the performance of the LTC3611. Please refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. Place jumpers in the following positions for a typical 1.8VOUT application: Vout Select RUN FCB 1.8V ON CCM 2. With power off, connect the input power supply, load and meters as shown in Figure 1. Preset the load to 0A and Vin supply to be less than 32V. 3. Turn on the power at the input. The output voltage should be 1.8V ± 2%. 4. Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. Output ripple should be measured across the output bulk capacitor as shown in Figure 2. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1318 HIGH INPUT VOLTAGE AND HIGH CURRENT DENSITY STEP-DOWN CONVERTER + – A V Vout + Vin – – + – V – Iout Load 0 -10A Vin A + – + Iin put transient current can be monitored at BNC connector J6 (5mV/A). Output voltage transient response should be measured at J5 with a BNC cable. + 5. For optional load transient test, apply adjustable pulse signal between IOSTEP CLK and GND pins. Pulse amplitude sets the current step. The pulse signal should have very small duty cycle (<5%) to limit the thermal stress on the transient load circuit. The out- Optional 5V Bias Figure 1. Proper Measurement Equipment Setup (EXTVCC Bias Supply is Optional) + Input or Output Capacitor Figure 2. Scope Probe Placements for Measuring Input or Output Ripple. 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1318 HIGH INPUT VOLTAGE AND HIGH CURRENT DENSITY STEP-DOWN CONVERTER 32Vin Efficiency vs. Load Current 90% 90% 85% 85% 80% 80% 75% 75% Efficiency Efficiency 24Vin Efficiency vs. Load Current 70% 65% 65% 1.5Vo 1.5Vo 1.8Vo 60% 70% 60% 1.8Vo 2.5Vo 55% 2.5Vo 3.3Vo 55% 50% 0 1 2 3 4 5 6 7 8 9 10 Load Current (A) 11 12 3.3Vo 50% 0 1 2 3 4 5 6 7 8 9 10 11 12 Load Current (A) Figure 3. Measured Supply Efficiency with Different VIN and VOUT Figure 4. Thermal image of DC1318 Vin = 24V Vout =1.8V Iout = 10A Tambient = 25°C, no forced airflow Cross 1: MOSFETs Cross 2: Inductor 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1318 HIGH INPUT VOLTAGE AND HIGH CURRENT DENSITY STEP-DOWN CONVERTER Vo(AC) 200mV/DIV Istep 4A/DIV Vin = 24V Vout =1.8V 2.5A to 7.5A LOAD STEP Cout = 2 X 22uF ceramic, X5R, 0805, 2X100uF ceramic, X5R, 1812 Figure 5. Measured Load Transient Response (2.5-7.5A Step, 25% to 75%) 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1318 HIGH INPUT VOLTAGE AND HIGH CURRENT DENSITY STEP-DOWN CONVERTER 5