DC1471A Analog Devices

DEMO CIRCUIT 1471 LT3990 QUICK START GUIDE LT3990 62V, 350mA Step-Down Regulator with 2.5A Quiescent Current and Integrated Diodes DESCRIPTION Demonstration circuit 1471 is a monolithic step- The catch diode and boost diode are integrated down DC/DC switching regulator featuring the to reduce the components count and solution LT3990. The switching frequency is adjustable size. The circuit consumes only 2.5A of quies- up to 2.2MHz. The demo circuit is designed for cent current. The current mode control scheme 5V, 350mA output from a 6.5V to 62V input. The creates fast transient response and good loop wide input range of the LT3990 allows a variety stability. The catch diode current is limited to of input sources including automotive batteries protect the part under short circuit and overvolt- and 24V industrial supplies. Low ripple Burst age conditions. Mode increases the efficiency at the light load The LT3990 datasheet gives a complete de- while keeping the output ripple below 5mV in a scription of the part, operation and application typical application. The part is in shutdown information. The datasheet must be read in con- when the EN pin is low and active when the pin junction with this quick start guide for demo cir- is high. The threshold of the EN pin is accurate cuit 1471. at 1V when Vin is above 4.2V. Adding a resistor Design files for this circuit board are avail- divider from Vin to EN can program the LT3990 able. Call the LTC factory. to regulate the output only when Vin is above a desired voltage. , LTC and LT are registered trademarks of Linear Technology Corporation. o Performance Summary (T = 25 C) A PARAMETER CONDITION VALUE Minimum Input Voltage 6.5V Maximum Input Voltage 62V Output Voltage V 5.04V 3% OUT Typical switching Frequency 400kHz Maximum Output Current 350mA Typical efficiency VIN=12V, Iout=350mA 83.27% Typical output voltage Ripple V =12V, I =350mA 15mV IN out QUICK START PROCEDURE NOTE. When measuring the input or output voltage ripple, care Demonstration circuit 1471 is easy to set up to must be taken to avoid a long ground lead on the oscilloscope evaluate the performance of the LT3990. Refer probe. Measure the input or output voltage ripple by touching the to Figure 1 for proper measurement equipment probe tip directly across the Vin or Vout and GND terminals. See Figure 2 for proper scope probe technique. setup and follow the procedure below: 1 GND VIN LT3990 1. Place JP1 on the ON position. 5. Once the proper output voltage is established, adjust the load within the 2. With power off, connect the input operating range and observe the out- power supply to Vin and GND. put voltage regulation, ripple voltage, 3. Turn on the power at the input. 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 Figure 2. Measuring Input or Output Ripple 2