DEMO MANUAL DC1725A LT3759 Wide Input Voltage Range Boost/SEPIC/Inverting Controller DESCRIPTION The LT3759 is a current mode DC/DC controller operating Demonstration circuit 1725A features LT3759 in a 485kHz over an input range of 1.6V to 42V, making it well suited boost converter, designed for a 5V/2A output from a 1.8V for applications ranging from single-cell lithium-ion bat- to 4.5V input. The demo circuit configures the shutdown tery portable electronics to high voltage automotive and voltage at typical 1.70V, which means that the input volt- industrial power supplies. It also exhibits low shutdown age can be dropped to as low as 1.70V, once it starts up. quiescent current of 1A, making it an ideal fit for battery The start-up voltage is set at 2.5V but can be adjusted by operated systems. Thanks to a novel FBX pin architecture, changing R1 and R2 values. the LT3759 can be connected directly to a divider from The LT3759 data sheet gives a complete description of the either a positive or negative output feedback voltage to part, operation and application information. The data sheet ground. It also packs many popular features such as soft- must be read in conjunction with this quick start guide. start, input undervoltage lockout, adjustable frequency and Design files for this circuit board are available at synchronization in a small 12-lead exposed pad MSOP DEMO MANUAL DC1725A QUICK START PROCEDURE Demo circuit 1725A is easy to set up to evaluate the per- NOTE: Make sure that the input voltage does not exceed formance of LT3759. Refer to Figure 1 for proper measure- 4.5V. If higher operating voltage is required, power ment equipment setup and follow the procedure below. components with higher voltage ratings should be used. 1. With power off, connect the input power supply, load 3. Once the proper output voltage is established, adjust and meters as shown in Figure 1. Preset the load to 0A, the input voltage and load within the operating range and V supply to be 0V. Place jumpers in the following and observe the output voltage regulation, ripple volt- IN positions for a typical 5V application: age, efficiency and other parameters. Typical efficiency curve is shown in Figure 3. EN (JP1) SYNC (JP2) NOTE: When measuring the input or output voltage ON OFF ripples, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or 2. Turn on V and increase slowly to 2.5V. Check for proper IN output voltage ripple by touching the probe tip directly output voltages. The output should be regulated at 5V across the V and GND, or V and GND terminals. IN OUT (3%). The switching frequency should be about 485kHz. See Figure 2 for proper scope probe technique. NOTE: If there is no output, or the output is out of spec, temporarily disconnect the load to make sure that the load is not set too high, and the power supply current capability is above 7A. Minimize voltage drop over the input wires. dc1725af 2