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LM2727: Deadtimes and low side MOSFET body diode reverse recovery

Maarten Verhage46
Prodigy 100 points
Part Number: LM2727
Other Parts Discussed in Thread: LM2737

Dear people of TI,

I was working on a design with a competitor buck synchronous switching controller. A little back ground on my design goals: input voltage is fixed 19V, output voltage should be controllable between 1V and 14V or s. And I'm looking for a fast one > 2MHz. This to be able to use a small inductor as well as using ceramic capacitors only on the input and output. Also the package have to be hand solder-able

But I realized their deadtimes where too long. Having both the body diode reverse recovery charge release and conduction losses. The LM2727 seems to be a better part in this regard. But little is told about the timing of the mosfet drives, hence the deadtimes in the datasheet.

My goal is to maximize power efficiency and I'm looking for a way to prevent the reverse recovery Qrr of the low side body diode to happen. My question is does the LM2727 already take care of this? As I did not found an equation like Pqrr = Qrr * Vds * Fsw, in the efficiency calculations in the datasheet.

Also I did not understand the specification that the LM2727 is not able to handle an input voltage above 16V. I know I should provide 5V to the chip Vcc pin, no problem. But why should the LM272 care if I provide 19V on the top mosfet drain pin? Could you explain that please?

Best regards,

Maarten Verhage

  • 0
    Prodigy 100 points
    Oh yeah, if TI can recommend better suitable parts for this application. That surely is welcome too!
  • 0 in reply to Maarten Verhage46
    TI__Mastermind 23815 points
    Hi Maarten,

    How about this one?
    www.ti.com/.../lmr33630.pdf

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Prodigy 100 points

    Hi Arief,

    Thanks for this suggestion. However I'd prefer one with external switches. So, as far as I can see the LM2727 or LM2737 looks the best. I hope TI is willing to answer my original questions to verify suitability for my application. I hope there is still knowledge within TI on this organically National Semiconductor part.

    On the first page of the datasheet I read: "The adaptive, nonoverlapping MOSFET gate-drivers and high-side bootstrap structure helps to further maximize efficiency." This looks to me as the original designers had already the intention to design it in such a way to prevent the body diode charge release Qrr. Now I hope this question will be handled by whoever is needed to answer this with confidence. If that is you, great. If that is not you, please forward this to the appropriate person.

    Best regards,

    Maarten Verhage