DEMO CIRCUIT 1544 LT3957 QUICK START GUIDE LT3957 Boost, SEPIC, Flyback and Inverting Converter with 5A, 40V Switch DESCRIPTION Demonstration circuit 1544 is a Boost, SEPIC, Flyback datasheet must be read in conjunction with this Quick and Inverting Converter with 5A, 40V Switch featuring Start Guide for demonstration circuit 1544A. The LT3957 the LT3957. The LT3957 can be configured as a boost, is assembled in a 36-lead plastic UHE package with two flyback, SEPIC, and inverting converter, but the demon- thermally enhanced pads for SW and GND. Proper board stration circuit is assembled as a boost. The input volt- layout is essential for both proper operation and maxi- age range is 4.5V to 20V and the output voltage is 24V mum thermal performance. See the datasheet section with 600mA over the entire input voltage range. Layout Considerations. The LT3957 has an internal n-channel 5A, 40V power switch for high voltage, power, and efficiency. The dual paddle package provides excellent heat dissipation for the internal power switch. The LT3957 current-mode dc/dc converter features adjustable switching frequency, soft-start, compensation, shutdown and undervoltage lockout with hysteresis, and a feedback pin (FBX) that can be used in both positive and negative applications. A SYNC input can be used to synchronize the switching at a frequency higher than the IC is programmed. The demonstration circuit features small 1210 case size Figure 1. DC1544A 12VIN Efficiency ceramic input and output capacitors. The internal n- channel power switch provides efficiency as high as 95% Design files for this circuit board are available. Call in typical boost applications with 14.4W output. the LTC factory. The LT3957 datasheet gives a complete description of L, LT are trademarks of Linear Technology Corporation. the part, operation and applications information. The PARAMETER CONDITIONS UNITS Minimum Input Supply Voltage 4.5 V Maximum Input Supply Voltage 20 V Output Voltage Programmed V = 4.5V-20V, I 600mA 24 V IN LOAD Switching Frequency R = 41.2k 300 kHz T Guaranteed Maximum Output current V = 4.5V-20V 600 mA IN Input Undervoltage Lockout (falling) R1=200k, R2=95.3k 3.8 V Input Turn-on Voltage (rising) R1=200k, R2=95.3k 4.2 v Efficiency V = 12V, I = 600mA 95 % IN LOAD 1 LT3957 QUICK START PROCEDURE NOTE. Connect power to GND, not SGND. Demonstration circuit 1544 is easy to set up to evaluate the performance of the LT3957. Refer to Figure 2 for 3. Connect a load of 600mA or less to VOUT and GND proper measurement equipment setup and follow the terminals (not SGND). procedure below: 4. Turn on the power at the input. NOTE. When measuring the input or output voltage ripple, care must be NOTE. Make sure that the input voltage does not exceed 20V. 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 5. Check for the proper output voltage (24V). Vin or Vout and GND terminals. NOTE. If there is no output, temporarily disconnect the load to make 1. Place jumpers in the following positions: sure that the load is not set too high. JP1 NO SYNC 6. Once the proper output voltage is established, adjust the load and input within the operating ranges and 2. With power off, connect the input power supply to observe the output voltage regulation, ripple voltage, VIN and GND. efficiency and other parameters. Figure 2. Proper Measurement Equipment Setup 2