DEMO MANUAL DC1891A LTC3862-2 Low Noise PolyPhase SEPIC DC/DC Converter DESCRIPTION Demonstration circuit 1891A is a 2-phase high efficiency Also, the DC1891A can be optimized for specific input volt- nonisolated SEPIC (single ended primary inductor con- ages. The narrowing of input voltage range can increase verter) converter featuring the LTC 3862-2 switching the converters efficiency. Therefore, a narrow input voltage controller. The DC1891A converts a 6V to 60V input to range is more desirable. a 12V output and provides 6A of output current. The The LTC3862-2 can be synchronized to an external clock converter operates at 300kHz (600kHz output ripple) with of up to 400kHz. Please refer to LTC3862-2 data sheet for efficiency around 90%. With a proper amount of airflow, design details and applications information. the DC1891A converter can generate over 6A of output Design files for this circuit board are available at current. The DC1891A can be easily modified to generate DEMO MANUAL DC1891A QUICK START PROCEDURE Demonstration circuit 1891A is easy to set up to evaluate 4. Once the proper output voltage is established, adjust the the performance of the LTC3862-2 circuit. Refer to Figure 1 load within the operating range and observe the output for proper measurement equipment setup and follow the voltage regulation, ripple voltage, efficiency and other procedure below: parameters. NOTE: When measuring the input or output voltage 5. The DC1891A is equipped with an input capacitor C IN4 ripple, care must be taken to avoid a long ground lead that is optional and is used to help with filtering when on the oscilloscope probe. Measure the input or output the board is connected to the lab supply with long leads. voltage ripple by touching the probe tip directly across The capacitor C can be removed if the input power IN4 the V or V and GND terminals. See Figure 2 for source is close and has low source impedance. IN OUT the proper scope probe technique. CHANGING THE OUTPUT VOLTAGE 1. With power off, connect the input power supply to V IN and GND. Make sure that the input power supply has To set the output voltage lower or higher than 12V, change sufficient current rating at minimum input voltage for the bottom voltage divider resistor connected to the FB the required output load. pin of U1 (see the Schematic Diagram). Also, check the MOSFET, output diode and capacitor voltage ratings if the 2. Turn on the power at the input. output voltage is set higher than 12V. NOTE: Make sure that the input voltage does not exceed The optional Q5 circuit is used to get the circuit running. 60V. Once the circuit is running, the 12V output is used to 3. Check for the proper output voltage. bias U1 via D2. The start-up circuit Q5 is turned off by Q6 V = 12V, 3%. when V gets to the level set by D3, R14 and R16 that OUT OUT activates Q6. Please contact the LTC factory for details. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. dc1891af 2