DEMO MANUAL DC2736A LTC7800EUDC High Frequency Synchronous Buck Converter with GaN Transistors DESCRIPTION Demonstration circuit 2736A is a single output high volt- The LTC7800 features two integrated 5V gate drivers with age nonisolated synchronous step-down converter that 20ns dead time which is good for GaN transistors or logic- drives all GaN transistor power stage. It features the level MOSFETs to maximize efficiency. The EXTV pin CC LTC 7800, a low quiescent current high frequency (pro- permits the LTC7800 to be powered from the output of grammable fixed frequency from 320kHz up to 2.25MHz) the switching regulator or other available source, reducing synchronous step-down DC/DC controller housed in a power dissipation and improving efficiency. Please refer small 3mm 4mm QFN package. to the LTC7800 data sheet for a complete description of the part operation and application information. This DC2736A operates over an input voltage range from 30V to 55V, while the LTC7800 can operate up to 60V. This Design files for this circuit board are available at demo board produces a 12V output voltage with up to 20A DEMO MANUAL DC2736A QUICK START PROCEDURE Demonstration circuit 2736A is easy to set up to evaluate Notes: the performance of the LTC7800. Refer to Figure 1 for 1. When measuring the output or input voltage ripple, the proper measurement equipment setup and follow the do not use the long ground lead on the oscilloscope procedure below. probe. See Figure 2 for the proper scope probe tech- 1. With board not connected, adjust the input power sup- nique. Short, stiff leads need to be soldered to the (+) ply to 48V, then turn off the input power supply. Make and () terminals of an output capacitor. The probes sure the input power supply is capable of 10A at 30V. ground ring needs to touch the () lead and the probe tip needs to touch the (+) lead. 2. With power off, connect the input power supply to V IN and GND terminal of the board. 2. Please set the electronic load in CR (constant resis- tance) mode for the evaluation of the board. The default 3. Connect the output load between V and GND (Initial OUT setup of the 2736A board is to have EXTV pin con- CC load: no load). Refer to Figure 1. nected to V . Some electronic load outputs nega- OUT 4. Connect the DVMs to the input and output. tive voltage when doing output overcurrent test of the board, which exceeds the absolute maximum rating 5. Check the default jumper/switch position: JP7: ON 0.3V on EXTV pin of LTC7800. CC JP13: CCM. 6. Turn on the input power supply. External EXTV Option CC NOTE: The input voltage range for the board is 30V to By default, the EXTV pin of LTC7800 on DC2736A board CC 55V. is connected to the output of the converter with R69 (0) for good efficiency and good thermal performance. Please 7. Check for the proper output voltage from V to OUT follow the below procedure if an external power supply is GND. The output voltage should be between 11.76V used to bias the LTC7800 EXTV pin (Do not float this CC to 12.24V. pin). 8. Once the proper output voltage is established, adjust 1. Remove R69 on the board. the loads within the operating range (0A to 20A) and observe the output voltage regulation, ripple voltage 2. Apply a DC voltage (recommend 5.5V 13V) on EXTV CC and other parameters. and GND turret after the input voltage is established. Make sure EXTV < V . CC IN 9. After completing all tests, adjust the load to 0A, turn off the input power supply. 3. Turn off the DC bias on the EXTV before powering CC off the input power supply. dc2736af 2