DEMO CIRCUIT 1050 LT3503 QUICK START GUIDE LT3503 1.2A, 2.2MHz Step-Down Switching Regulator in 2mm×3mm DFN DESCRIPTION Demonstration circuit 1050 is a monolithic step-dow n DC/DC sw itching regulator featuring LT3503. The demo board is designed for 3.3V output from a 4.5V to 20V input. The w ide input range of the LT3503 allow s a variety of input sources. The typical sources are automotive batteries, w all adaptors and industrial supplies. The 2.2M H 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 internal compensation reduces the component count and solution size. 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. A charge pump consisting of a diode and capacitor on the demo board performs the boost function. The SH DN pin can be used to set the part in micropow er shutdow n mode, reducing the supply current to less than 2uA. The SH DN pin can also be used to program soft start. In this mode, the SH DN 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. Cycle by cycle current limit, frequency foldback and thermal shutdow n provide the protection against shorted outputs. The LT3503 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 1050. Design files for this circuit board are available. Call the LTC factory. ,LTC and LT are registered trademarks ofLinear Technology Corporation. ThinSOT and Pow erPath are trademarks ofLinear Technology Corporation. Performance Summary ( TA = 25oC ) PAR AM ETER FO R STEP-DO W N CON VERTER M inimum input voltage M aximum input voltage O utput voltage VOUT M aximum output current M aximum output current Typical sw itching frequency CO N DITIO N VALU E 4.5V 20V 3.3V +/- 4% 1A 1.2A 2.2M H z VIN = 5.5V VIN = 8.5V QUICK START PROCEDURE Demonstration circuit 1050 is easy to set up to evaluate the performance of the LT3503. 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 in 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 pow er at the input. NOTE. M ake sure that the input voltage does not exceed 20V. 4. Check for proper output voltages. NOTE. Ifthere is no output,temporarily disconnect the load to make sure that the load is not set too high. 1 LT3503 O nce the proper output voltages are established, adjust the loads w ithin the operating range and observe A _+ _ _ + + V the output voltage regulation, ripple voltage, efficiency and other parameters. Load A V _ + _ 5. + _ + Figure 1. Proper M easurem ent Equipm ent Setup GND VIN Figure 2. M easuring Input or Output Ripple 2 LT3503 3