DEMO CIRCUIT 1244 QUICK START GUIDE LOW QUIESCENT CURRENT, DUAL OUTPUT HIGH VOLTAGE STEPDOWN CONVERTER DESCRIPTION Demonstration circuit 1244 is a Low Quiescent Current, Dual Output Synchronous Buck Converter featuring the LTC3890EGN-1. DC1244 converts a 4.5V-60V voltage source to 3.3V at 5.0A and 8.5V at 3.0A. When the input voltage is close or below 9V, 8.5V output enters into dropout mode. The main features of the board include an external 5V linear regulator for bias, RUN1, RUN2, PGOOD1 pins and a Mode selector that allows converter to run in CCM or Burst Mode operation. DC1244 supports also Pulse Skipping Mode, adjustable output voltage, Soft-Start and Tracking. Synchronization to an external clock is possible as well. The wide input voltage range of 4.5V to 60V is suitable for automotive or other battery fed application and Distributed DC Power Systems where low quiescent current is important. The LTC3890EGN-1 datasheet gives a complete description of these parts, operation and application informa- PARAMETER Minimum Input Supply Voltage Maximum Input Supply Voltage Output Voltage Range (VOUT1) Output Voltage Range (VOUT2) Typical switching frequency Typical Output Ripple (VOUT1, 3.3V) Typical Output Ripple (VOUT2, 8.5V) Efficiency Typical (VOUT1, 3.3V) Efficiency Typical (VOUT2, 8.5V) tion. The datasheets must be read in conjunction with this quick start guide for demo circuit 1244. The 60V avalanche rated MOSFETs, which are used on DC1244, can be operated at their rated voltage. However, if application derating requirements are stricter, MOSFETs with higher voltage rating can be used. Please note, MOSFETs with higher voltage ratings may affect the efficiency. If 60V MOSFETs are used, keep in mind that avalanche rating and testing is typically done with 30% over voltage margin (78V for 60V rated MOSFET). Please check with particular MOSFET manufacturer to ensure the avalanche voltage rating. Design files for this circuit board are available. Call the LTC factory. L, LTC, LTM, LT are registered trademarks of Linear Technology Corporation. CONDITIONS VIN = 4.5V to 60V, IOUT1 = 0A to 5A VIN = 9V to 60V, IOUT2 = 0A to 3A ILOAD = 5.0A ILOAD = 3.0A VOUT1 is ON, VOUT2 is OFF VOUT1 is OFF, VOUT2 is ON VALUE 4.5 60 3.3±2% 8.5±2% 225 40 60 92 96 UNITS V V V V kHz mV mV % % 1 QUICK START PROCEDURE Demonstration circuit 1244 is easy to set up to evaluate the performance of the LTC3890EGN-1. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE. When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the VIN or VOUT and GND terminals. See Figure 2 for proper scope probe technique. 2. With power off, connect the input power supply to VIN and GND. 3. Turn on the power at the input. Check for the proper output voltages VOUT1=3.23V to 3.37V, VOUT2 = 8.33V to 8.67V NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 1. Place jumpers in the following positions: 4. 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. JP4 RUN1 ON, JP3 RUN2 ON, Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or output Ripple 2 DC1244, LTC3890EGN-1, VIN 10V to 60V 100 95 90 % 85 10V 80 30V 60V 75 70 65 60 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 A Figure 3. 3.3V Output, Efficiency vs. Load DC1244, LTC3890EGN-1, VIN 10V to 60V 100 98 96 % 94 10V 92 30V 90 60V 88 86 84 82 0.5 1 1.5 2 2.5 3 A Figure 4. 8.5V Output, Efficiency vs. Load 3 4