DEMO MANUAL DC2393A LT8304 Micropower No-Opto Isolated Flyback Converter with 150V/2A Switch DESCRIPTION Demonstration circuit 2393A is a micropower no-opto The LT8304 is a simple to use monolithic micropower isolated flyback converter featuring the LT 8304. This isolated flyback converter. By sampling the isolated output demo circuit outputs 5.0V, and maintains tight regula- voltage directly from the primary-side flyback waveform, tion with a load current from 20mA up to 4.2A and over the part requires no third winding or opto-isolator for an input voltage from 18V to 72V. The output current regulation. The output voltage is programmed with two capability increases with the input voltage, as shown in external resistors and a third optional temperature compen- the Performance Summary table. sation resistor. By integrating the loop compensation and soft-start inside, the part reduces the number of external The DC2393A needs less than 0.5% of its full output power components. Boundary mode operation provides a small as a minimum load to maintain good output voltage regu- magnetic solution with excellent load regulation. Low lation. On the DC2393A, in order to avoid pre-loading, a ripple Burst Mode operation maintains high efficiency + 5.6V Zener diode is placed between its V and V to OUT OUT at light load while minimizing the output voltage ripple. A serve as a minimum load. 2A, 150V DMOS power switch is integrated along with all Transformer leakage inductance causes a voltage spike the high voltage circuitry and control logic into a thermally on the primary side after the power switch turns off. To enhanced 8-lead SO package. limit this leakage inductance spike within MOSFET volt- The LT8304 data sheet gives a complete description of age rating of 150V, an RC snubber and a TVS clamp are the part, operation and application information. The data installed to damp the ringing and clamp the MOSFET drain sheet must be read in conjunction with this quick start voltage to a safe level. guide for demo circuit 2393A The Performance Summary table summarizes the perfor- Design files for this circuit board are available at mance of the demo board at room temperature. The demo DEMO MANUAL DC2393A QUICK START PROCEDURE Demonstration circuit 2393A is easy to set up to evalu- Note: The LT8304 requires very small minimum load ate the performance of the LT8304. Refer to Figure 1 for to maintain good output voltage regulation. A Zener proper measurement equipment setup and follow the diode is placed on the output to clamp the voltage to procedure below: 5.6V. This Zener can be replaced with a 249 resistor at the trade off of lower efficiency. 1. With power off, connect the input power supply to the board through V (E1) and GND (E2) terminals. Connect 4. Once the proper output voltage is established, adjust IN + the load to the terminals V (E3) and V (E4) on the input voltage and load current within the operating OUT OUT the board. range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 2. Turn on the power at the input. Increase V slowly IN to18V. NOTE: When measuring the input or output voltage ripples, care must be taken to avoid a long ground lead on the Note: Make sure that the input voltage is always within oscilloscope probe. Measure the input or output voltage spec. To operate the board with higher input/output ripple by touching the probe tip directly across the V (E1) IN voltage, input capacitor, output capacitor and output + and GND (E2), or V (E3) and V (E4) terminals. OUT OUT diode with higher voltage ratings are needed. See Figure 2 for proper scope probe technique. 3. Check for the proper output voltages. The output should be regulated at 5.0V (5%). Figure 1. Proper Measurement Equipment Setup dc2393af 2