QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1311 TELECOM DC/DC CONVERTER LTC3805/-5 DESCRIPTION Demonstration circuit 1311 is a Telecom isolated output voltage is increased, the maximum DC/DC converter featuring the LTC3805/-5 constant output current must be reduced to limit the frequency current mode flyback controller. The output power to no more than 10W. Higher DC1311 converts 18V to 72V input voltage to an output voltages and currents can be achieved by isolated 3A of output current at 3.3V. The 300kHz changing the MOSFET, transformer and output constant frequency operation is maintained down to capacitors. Please consult LTC factory for details. very light load to reduce low frequency noise The DC1311 has a small circuit footprint. It is a high generated over a wide range of load current. The performance and cost effective solution for Telecom, converter provides high output voltage accuracy Automotive and Power over Ethernet applications. (typically 2%) over wide load range with no minimum load requirement. Design files for this circuit board are available. Call The DC1311 also provides non-isolated design by the LTC factory. removing opto coupler and LTC4430 circuit. The demonstration circuit can be easily modified to LTC and LT are registered trademarks of Linear Technology Corporation. generate different output voltages up to 15V. As QUICK START PROCEDURE Demonstration circuit 1311 is easy to set up to power components with higher voltage ratings evaluate the performance of the LTC3805/-5. For should be used. proper measurement equipment setup refer to 4. Check for proper output voltage. Vout=3.3V. Figure 1 and follow the procedure below. If there is no output, temporarily disconnect the When measuring the input or output voltage ripple, load to make sure that the load is not set too high. care must be taken to minimize the length of the 5. To shut the converter down, move the RUN switch oscilloscope probe ground lead. Measure the input or into OFF position output voltage ripple by connecting the probe tip directly across the V or V and GND terminals, IN OUT 6. To synchronize converter to external clock, set see Figure 2. jumper JP2 (SYNC) to EXT position, apply signal to FSET pin. See LTC3805/-5 datasheet for 1. With power off, connect the input power supply to synchronization signal parameters. +Vin and -Vin. 7. Once the proper output voltage is established, 2. Move the J1 (RUN) switch to ON position. adjust the load within 3.0A range and observe the 3. Turn the input power source on and slowly output voltage regulation, ripple voltage, efficiency increase the input voltage. Be careful not to exceed and other parameters. 72V. Make sure that the input voltage V does not IN exceed 72V. If higher operating voltage is required, 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1311 TELECOM DC/DC CONVERTER Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2