DEMO CIRCUIT 1089 LT3502A QUICK START GUIDE LT3502A 2.2MHz, 500mA, Step-down Regulator in 2mm × 2mm DFN DESCRIPTION Demonstration circuit 1089 is a monolithic step-down DC/DC switching regulator featuring the LT3502A. The demo circuit is designed for 5V output from a 7V to 40V input. The wide input range of the LT3502A allows a variety of input sources including automotive batteries and 24V industrial supplies. The high switching frequency allows the use of tiny, low cost external components. Constant switching frequency above the AM band avoids interfering with radio reception. The current mode control scheme creates fast transient response and good loop stability. The boost diode is internal to reduce component count. The SHDN pin can also be used to program soft start. In this mode, the SHDN pin is driven through an external RC 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 and frequency foldback provide the protection against shorted outputs. DA pin can further protect the silicon under fault conditions by sensing the diode current. The LT3502A datasheet gives a complete description of the part, operation and application information. The datasheet must be read in conjunction with this quick start guide for demo circuit 1089. Design files for this circuit board are available. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. Performance Summary (TA = 25oC) PARAMETER Minimum Input Voltage Maximum Input Voltage Output Voltage VOUT Switching Frequency Maximum Output Current Efficiency Voltage Ripple CONDITION VIN = 12V, IOUT = 500mA VIN = 12V, IOUT = 500mA VALUE 7V 40V 4.98V ±3% 2.25MHz 500mA 84% 10mV QUICK START PROCEDURE Demonstration circuit 1089 is easy to set up to evaluate the performance of the LT3502A. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE. When measuring the input or output voltage ripple, care must be 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 VIN or VOUT and GND terminals. See Figure 2 for proper scope probe technique. 1. Place JP1 on the ON position. 2. With power off, connect the input power supply to Vin and GND. 3. Turn on the power at the input. NOTE. Make sure that the input voltage does not exceed 40V. 4. Check for the proper output voltages. NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 5. Once the proper output voltage is established, adjust the load within the operating range and observe the 1 LT3502A output voltage regulation, ripple voltage, efficiency and other parameters. Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 2 LT3502A TRANSIENT RESPONSE The demo board 1089 is optimized for size. A feedforward capacitor is used to ensure the good transient performance. Figure 3 shows the transient response of the demo board. The input voltage is 12V. The output voltage is 5V and the load current is stepped from 150mA to 400mA. IL 200mA/DIV Vout 100mV/DIV AC coupled 10μs/DIV Figure 3. Transient Response 3 LT3502A 4