JAJSDG8F July 2011 – March 2018 LM25118
PRODUCTION DATA.
A Schottky type recirculating diode is required for all LM25118 applications. The near ideal reverse recovery characteristics and low forward voltage drop are particularly important diode characteristics for high input voltage and low output voltage applications. The reverse recovery characteristic determines how long the current surge lasts each cycle when the buck switch is turned on. The reverse recovery characteristics of Schottky diodes minimize the peak instantaneous power in the buck switch during the turn-on transition. The reverse breakdown rating of the diode should be selected for the maximum VIN plus some safety margin.
The forward voltage drop has a significant impact on the conversion efficiency, especially for applications with a low output voltage. Rated current for diodes vary widely from various manufacturers. For the LM25118 this current is user selectable through the current sense resistor value. Assuming a worst-case, 0.6-V drop across the diode, the maximum diode power dissipation can be high. The diode should have a voltage rating of VIN and a current rating of IOUT. A conservative design would at least double the advertised diode rating because specifications between manufacturers vary. For the reference design, a 100-V, 10-A Schottky in a D2PAK package was selected.