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LM5145EVM-HD-20A: Question on Schottky diode used with synchronous rectifier

Chris Cencula38
Prodigy 120 points
Part Number: LM5145EVM-HD-20A
Other Parts Discussed in Thread: LM5145

The evaluation board has a Schottky diode in parallel with the lower FET (synchronous rectifier), but the WebBench tools and also LM5145 DC-DC Controller Design Tool (Spreadsheet) don't show use of such part.

Why is this part incorporated on the evaluation board (but not in online design tool references)?

Under what circumstances is it useful (or not)?

Best regards,
Chris Cencula

  • 0
    TI__Genius 10720 points

    Hi Chris,

    The Schottky diode placed across the lower FET (LSFET) actually creates a lower loss conduction path for current to flow when the higher FET (HSFET) turns off.  Rather than allowing current to flow through the LSFET body diode during dead time, the current will flow through the Schottky diode which has a forward voltage drop lower than that of the LSFET body diode. When the LSFET turns ON fully, the Schottky will cease to conduct. In other words, the Schottky reduces switching losses.

    I hope this answers your question. Feel free to post a follow-up if you have additional questions.

    Regards,

    Harrison Overturf