DEMO CIRCUIT 1412A QUICK START GUIDE LT3758 LT3758EMSE FLYBACK CONVERTER DESCRIPTION Demonstration circuit 1412A features LT3758EMSE in a 300kHz Flyback converter circuit, designed for 3.3V output from a 18V to 75V input. The LT3758EMSE operates over an input range of 5.5V to 100V, suitable for automotive, telecom and industrial applications. It also exhibits low shutdown quiescent current of 1µA, making them an ideal fit for battery-operated systems. Thanks to a novel FBX pin architecture, the LT3758EMSE can be connected directly to a divider from either the positive output or the negative output to ground. It also packs many popular features such as soft-start, input under- voltage lockout, adjustable frequency and synchronization in a small 10-lead MSOP package or a 3mm × 3mm QFN package. The LT3758EMSE datasheet gives a complete description of the part, operation and application information. The datasheet must be read in conjunction with this quick start guide for demo circuit 1412A. Design files for this circuit board are available. Call the LTC factory. LT, LTC, LTM and are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. o Table 1. Performance Summary for 300kHz Flyback Regulator ( TA = 25 C ) PARAMETER CONDITION Minimum Input Voltage Maximum Input Voltage Output Voltage VOUT Maximum Output Current Typical Switching Frequency VALUE 18V 75V 3.3V +/-3% 3A 300kHz QUICK START PROCEDURE Demonstration circuit 1412A is easy to set up to evaluate the performance of the LT3758EMSE. 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. 1. Place JP1 on the ON position. 3. Turn on the power at the input. NOTE. Make sure that the input voltage does not exceed the maximum input voltage. 4. Check for the proper output voltages. NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 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. 2. With power off, connect the input power supply to Vin and GND. 1 LT3758 Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2 GND OFF ON E6 18V - 75V JP1 RUN 3 2 1 OPT R2 R7 1% 1% 105K R8 VIN 8.66K OPT C3 100pF C2 OPT 1% 36.5K R5 0 R6 U1 4 2 9 1 3 RT FB SYNC SENSE GATE I NTVCC VIN SHDN/U VLO VC SS LT3758EMSE C6 0.1uF R16 100V 1uF 100V 1uF CIN2 CIN1 5 6 7 8 OPT C16 R21 6.81K 1% R20 50V 4.7uF C1 4700pF C8 10K R9 0 R4 0 D5 2 2 E7 SYNC 4 Si4848DY Q2 BAS516 1 D2 BAV21W 1 220pF C10 51.1 1% R1 10K R3 3 4 0.040 RCS1 5 6 7 8 1 2 3 7 8 5 6 R10 OPT 2200pF 250V C9 2 1 BAS516 PS2801-1 U4 D3 PA1277NL 1 2 3 T1 0.47uF C7 1uF C4 499 1% R11 C15 OPT 0 R18 1 3 2 3 2 1 OC GND VI N FB COM P OPTO LT4430ES6 U3 BAT54C 4 5 10nF C5 VOUT 6.3V 100uF 1% 22.1K R13 4.22K 1% 1% 100K R14 0 E4 E1 270pF C12 VOUT Co3 R15 R12 OPT 6.3V 6.3V C11 100uF 100uF 6 Co2 Co1 D4 VOUT UPS840 D1 2 4 1 VIN 10 V IN GND 11 VIN 3 E5 SEC. RTN 3.3V / 3A +VOUT LT3758 3