DEMO CIRCUIT 1323 LT3686 QUICK START GUIDE LT3686EDD 37V, 1.2A, Buck Regulator DESCRIPTION Demo circuit 1323 is a current-mode PWM step-down frequency at light loads, resulting in low, predictable out- DC/DC regulator with an internal 1.2A power switch fea- put ripple above the audio and AM bands. Internal com- turing the LT3686. The demo circuit is designed for 3.3V pensation and an internal boost diode reduce external output from a 5V to 37V input. The wide input range of component count. the LT3686 allows a variety of input sources. The typical The LT3686 datasheet gives a complete description of sources are automotive batteries and industrial supplies. the part, operation and application information. The data- Its high maximum frequency allows the use of tiny in- sheet must be read in conjunction with this quick start ductors and capacitors. Operating frequency above the guide for Demo Circuit 1323. AM band avoids interfering with radio reception, making LT3686 is available in 3mmx3mm DFN package. the LT3686 particularly suitable for automotive applica- tions. Design files for this circuit board are available. Call the LTC factory. Cycle by cycle current limit and DA current sense provide the protection against shorted outputs. Soft-start and , LTC, LTM, LT and uModule are registered trademarks of Linear Technology Corporation. frequency foldback eliminate input current surge during All other trademarks are the property of their respective owners. startup. An optional internal regulated active load at the output via the BD pin keeps the LT3686 at full switching o Performance Summary ( T = 25 C ) A PARAMETER CONDITION VALUE Minimum Input Voltage 5V Maximum Input Voltage 37V Output Voltage V 3.3V 3% OUT Switching Frequency 1MHz Maximum Output Current V =5~37V 1.2A IN Efficiency V =12V, I =1.0A 80.7% IN OUT Voltage Ripple V =12V, I =1.0A 20mV IN OUT 1 GND VIN LT3686 QUICK START PROCEDURE Demonstration circuit 1323 is easy to set up to evaluate 3. Turn on the power at the input. the performance of the LT3686. Refer to Figure 1 for NOTE. Make sure that the input voltage does not exceed 55V. proper measurement equipment setup and follow the 4. Check for the proper output voltage. procedure below: NOTE. If there is no output, temporarily disconnect the load to make NOTE. When measuring the input or output voltage ripple, care must be sure that the load is not set too high. 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. Once the proper output voltage is established, adjust Vin or Vout and GND terminals. See Figure 2 for proper scope probe the load within the operating range and observe the technique. output voltage regulation, ripple voltage, efficiency 1. Place JP1 on the ON position. and other parameters. 2. With power off, connect the input power supply to Vin and GND. Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2