DEMO MANUAL DC1722A LTC3864 55V Low I Step-Down Q DC/DC Converter with 100% Duty Cycle Capability DESCRIPTION Demonstration circuit 1722A is a high voltage, current for larger MOSFET and diode packages on the back of the mode DC/DC step-down converter featuring the LTC 3864. board for higher output current requirements. The board operates from an input range of 3.5V to 55V, This board is suitable for a wide range of automotive, and provides a 5V, 2A output when the input exceeds 5V. telecom, industrial, and other applications. The LTC3864 The PMOSFET architecture allows it to operate seamlessly is available in small 12-pin thermally enhanced MSOP and up to 100% duty cycle, and function as a saturated switch DFN packages. For other output requirements, see the below the regulation threshold, down to 3.5V . It operates LTC3864 data sheet or contact the LTC factory. IN at 350kHz and may be synchronized to an external clock. Design files for this circuit board are available at A soft-start feature controls output voltage slew rate at DEMO MANUAL DC1722A QUICK START PROCEDURE Demonstration circuit 1722 is easy to set up to evaluate 3. Turn on the power at the input. the performance of the LTC3864. Refer to Figure 1 for NOTE: Make sure that the input voltage never exceeds 55V. proper measurement equipment setup and follow the 4. Check for the proper output voltage of 5V. Turn off the procedure below: power at the input. NOTE: When measuring the output voltage ripple, care must 5. Once the proper output voltage is established, connect be taken to avoid a long ground lead on the oscilloscope a variable load capable of sinking 2A at 5V to the output probe. Measure the output voltage ripple by touching the terminals V and GND. Set the current for 0A. probe tip and ground ring directly across the last output OUT capacitor as shown in Figure 1. a. If efficiency measurements are desired, an ammeter or a resistor shunt that is capable of handling 2A 1. Set an input power supply that is capable of 3.5V to DC can be put in series with the output load in order to 55V to 6V. Then turn off the supply. measure the DC1722As output current. 2. With power off, connect the supply to the input terminals b. A voltmeter with a capability of measuring at least 5V V and GND. IN can be placed across the output terminals in order a. Input voltages lower than 3.5V can keep the converter to get an accurate output voltage measurement. from turning on due to the undervoltage lockout 6. Turn on the power at the input. feature of the LTC3864. NOTE: If there is no output, temporarily disconnect b. If efficiency measurements are desired, an ammeter the load to make sure that the load is not set too high. capable of measuring 2A or a resistor shunt can DC be put in series with the input supply in order to 7. Once the proper output voltage is again established, measure the DC1722As input current. adjust the load and/or input within the operating range and observe the output voltage regulation, ripple volt- c. A voltmeter with a capability of measuring at least age, efficiency and other desired parameters. 55V can be placed across the input terminals in order to get an accurate input voltage measurement. dc1722afa 2