DEMO CIRCUIT 1188 LT3684 QUICK START GUIDE LT3684EMSE 2A, 34V Step-Down Switching Regulator DESCRIPTION Demonstration circuit 1188 is a monolithic step-dow n DC/DC sw itching regulator featuring the LT3684. The demo circuit is designed for a 3.3V output from a 4.5V to 34V input. The w ide input range of the LT3684 allow s a variety of input sources. The typical sources are automotive batteries, w all adaptors and industrial supplies. The programmed 800kH z sw itching frequency allow s the use of small, low cost inductor and ceramic capacitors, resulting in low , predictable output ripple. The current mode control scheme creates fast transient response and good loop stability. The gate drive of the internal sw itch is boosted to a voltage that is higher than the Vin to ensure saturation of the sw itch. The LT3684’s integrated boost diode reduces the parts count. The R U N /SS pin can be used to set the part in micropow er shutdow n mode, reducing the supply current to less than 1uA. The R U N /SS pin can also be used to program soft start. In this mode, the R U N /SS pin is driven through an external R C filter to create a voltage ramp on this pin. The soft start function reduces the input current surge during start-up. The LT3684 datasheet gives a complete description of the part,operation and application information. The datasheet must be read in conjunction w ith this quick start guide for demo circuit 1188. Design files for this circuit board are available. Call the LTC factory. ,LTC and LT are registered trademarks ofLinear Technology Corporation. Perform ance Sum m ary for Step-dow n Sw itching Regulator (TA = 25oC ) PAR AM ETER FO R BU CK R EG U LATO R M inimum Input Voltage M aximum Input Voltage O utput Voltage VOUT M aximum O utput Current Typical Sw itching Frequency CO N DITIO N VALU E 4.5V 34V 3.3V +/- 4% 2A 800kH z QUICK START PROCEDURE Demonstration circuit 1188 is easy to set up to evaluate the performance of the LT3684. R efer to Figure 1 for proper measurement equipment setup and follow the procedure below : NOTE. W hen measuring the input or output voltage ripple,care must be taken to avoid a long ground lead on the oscilloscope probe. M easure 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 R U N position: 2. W ith pow er off,connect the input pow er supply to Vin and G N D. 3. Turn on the pow er at the input. NOTE. M ake sure that the input voltage does not exceed the maximum input voltage. 4. Check for the proper output voltage. NOTE. Ifthere is no output,temporarily disconnect the load to make sure that the load is not set too high. 5. O nce the proper output voltage is established, adjust the load w ithin the operating range and observe the output voltage regulation,ripple voltage,efficiency and other parameters. 1 LT3684 A A + + _ + V _ + _V + Load _ _ Figure 1. Proper M easurem ent Equipm ent Setup GND VIN Figure 2. M easuring Input or Output Ripple 2 LT3684 3