DEMO CIRCUIT 1471 LT3990 QUICK START GUIDE LT3990 62V, 350mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes DESCRIPTION Demonstration circuit 1471 is a monolithic stepdown DC/DC switching regulator featuring the LT3990. The switching frequency is adjustable up to 2.2MHz. The demo circuit is designed for 5V, 350mA output from a 6.5V to 62V input. The wide input range of the LT3990 allows a variety of input sources including automotive batteries and 24V industrial supplies. Low ripple Burst Mode increases the efficiency at the light load while keeping the output ripple below 5mV in a typical application. The part is in shutdown when the EN pin is low and active when the pin is high. The threshold of the EN pin is accurate at 1V when Vin is above 4.2V. Adding a resistor divider from Vin to EN can program the LT3990 to regulate the output only when Vin is above a desired voltage. Performance Summary (TA = 25oC) PARAMETER Minimum Input Voltage Maximum Input Voltage Output Voltage VOUT Typical switching Frequency Maximum Output Current Typical efficiency Typical output voltage Ripple The catch diode and boost diode are integrated to reduce the components count and solution size. The circuit consumes only 2.5µA of quiescent current. The current mode control scheme creates fast transient response and good loop stability. The catch diode current is limited to protect the part under short circuit and overvoltage conditions. The LT3990 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 1471. Design files for this circuit board are available. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. CONDITION VIN=12V, Iout=350mA VIN=12V, Iout=350mA VALUE 6.5V 62V 5.04V ±3% 400kHz 350mA 83.27% 15mV QUICK START PROCEDURE Demonstration circuit 1471 is easy to set up to evaluate the performance of the LT3990. 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 LT3990 1. 2. 3. Place JP1 on the ON position. 5. With power off, connect the input power supply to Vin and GND. Turn on the power at the input. Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. NOTE. Make sure that the input voltage does not exceed 62V. 4. Check for the proper output voltage. NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 2 OFF ON EN/UVLO PG GND E5 E6 E4 E3 VIN 6.5V - 62V JP1 3 2 1 (Opt) R8 VOUT C4 10uF 100V VIN + VIN 100K 0402 R6 C3 2.2uF 100V 1210 R7 (Opt) 3 5 7 10 12 15 4 14 6 NC NC NC NC NC NC EN/UVLO PG VIN 8 17 GND GND U1 LT3990EMSE RT FB FB BD BOOST SW 16 1 2 13 11 9 R5 374K 1% 0402 (400kHz) C2 0.22uF 16V 0603 L1 33uH LPS6225-333ML R2 316K 1% R1 1.00M 1% C5 22pF C1 22uF 10V 1206 VOUT E2 E1 GND VOUT 5V / 350mA LT3990 3