DEMO CIRCUIT 1341A L T3757 QUICK START GUIDE LT3757EDD HIGH EFFICIENCY SEPIC CONVERTER DESCRIPTION Demonstration circuit 1341A features LT3757EDD in a as soft-start, input undervoltage lockout, adjustable 300kHz SEPIC converter circuit, designed for 5V out- frequency and synchronization in a small 10-lead put from a 4.5V to 36V input. MSOP package or a 3mm 3mm QFN package. The LT3757EDD operates over an input range of 2.9V The LT3757EDD datasheet gives a complete descrip- to 40V, suitable for applications from single-cell lith- tion of the part, operation and application information. ium-ion battery portable electronics up to high voltage The datasheet must be read in conjunction with this automotive and industrial power supplies. It also ex- quick start guide for demo circuit 1341A. hibits low shutdown quiescent current of 1A, making Design files for this circuit board are available. Call them an ideal fit for battery-operated systems. The IC the LTC factory. integrates a high voltage, low dropout linear (LDO) regulator. Thanks to a novel FBX pin architecture, the , LTC and LT are registered trademarks of Linear LT3757EDD can be connected directly to a divider Technology Corporation. from either the positive output or the negative output to ground. They also pack many popular features such o Table 1. Performance Summary for 300kHz SEPIC Regulator ( TA = 25 C ) PARAMETER CONDITION VALUE Minimum Input Voltage 4.5V Maximum Input Voltage 36V Output Voltage V 5V +/-3% OUT Maximum Output Current 3A Typical Switching Frequency 300kHz QUICK START PROCEDURE Demonstration circuit 1341A is easy to set up to 3. Turn on the power at the input. evaluate the performance of the LT3757EDD. Refer NOTE. Make sure that the input voltage does not to Figure 1 for proper measurement equipment exceed the maximum input voltage. setup and follow the procedure below: 4. Check for the proper output voltages. NOTE. When measuring the input or output voltage NOTE. If there is no output, temporarily disconnect ripple, care must be taken to avoid a long ground the load to make sure that the load is not set too lead on the oscilloscope probe. Measure the input high. or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. Once the proper output voltages are established, See Figure 2 for proper scope probe technique. adjust the loads within the operating range and ob- serve the output voltage regulation, ripple voltage, 1. Place JP1 on the RUN position. efficiency and other parameters. 2. With power off, connect the input power supply to Vin and GND. 1 L T3757 Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2