DEMO CIRCUIT 1527 LT3971 QUICK START GUIDE LT3971 38V, 1.2A Micropower Buck Regulator DESCRIPTION Demonstration circuit 1527 is a monolithic step-down The circuit consumes only 2.8A of quiescent current. DC/DC switching regulator featuring the LT3971. The The boost diode, control and logic circuit are inte- switching frequency is adjustable up to 2MHz. The grated to reduce the components count and solution demo circuit is designed for 3.3V, 1.2A output from a size. The current mode control scheme creates fast 4.5V to 38V input. The wide input range of the LT3971 transient response and good loop stability. allows a variety of input sources including automotive The LT3971 datasheet gives a complete description of batteries and 24V industrial supplies. Low ripple Burst the part, operation and application information. The Mode increases the efficiency at the light load while datasheet must be read in conjunction with this quick keeping the output ripple below 15mV. The part is in start guide for demo circuit 1527. shutdown when the EN pin is low and active when the Design files for this circuit board are available. Call pin is high. The threshold of the EN pin is accurate at the LTC factory. 1V with 30mV of hysteresis. When Vin is above 6V, adding a resistor divider from Vin to EN can program , LTC and LT are registered trademarks of Linear Technology Corporation. the LT3971 to regulate the output only when Vin is above a desired voltage. o Performance Summary (T = 25 C) A PARAMETER CONDITION VALUE Minimum Input Voltage 4.5V Maximum Input Voltage 38V Output Voltage V 3.3072.5% OUT Typical switching Frequency 800kHz Maximum Output Current 1.2A Typical efficiency V =12V, I =1.2A 82.43% IN out Typical output voltage Ripple V =12V, I =1.2A 10mV IN out QUICK START PROCEDURE Demonstration circuit 1527 is easy to set up to 1. Place JP1 on the ON position. evaluate the performance of the LT3971. Refer to 2. Place JP2 on the RT FREQ position. Figure 1 for proper measurement equipment setup 3. With power off, connect the input and follow the procedure below: power supply to Vin and GND. NOTE. When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. 4. Turn on the power at the input. Measure the input or output voltage ripple by touching the probe tip NOTE. Make sure that the input voltage does not exceed 38V. directly across the Vin or Vout and GND terminals. See Figure 2 for proper scope probe technique. 5. Check for the proper output voltage. 1 GND VIN LT3971 NOTE. If there is no output, temporarily disconnect the load to voltage regulation, ripple voltage, effi- make sure that the load is not set too high. ciency and other parameters. 6. Once the proper output voltage is es- tablished, adjust the load within the op- erating range and observe the output Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2