Logic level MOSFET (3.3v)

Discussion in 'Analog & Mixed-Signal Design' started by daman, Jun 27, 2016.

  1. daman

    Thread Starter New Member

    Jun 14, 2012
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    Hi,

    I'm trying to drive 4A load (@18V) from 3.3V MCU. There's not that many MOSFETs (N) that can do it but I found this one and it looks promising:
    2SK4043LS http://media.digikey.com/pdf/Data Sheets/ON Semiconductor PDFs/2SK4043LS.pdf
    Could somebody have a look ant tell me if it's suitable...?
    I also found the following: CPH3442 (http://datasheet.octopart.com/CPH3442-TL-E-Sanyo-datasheet-7588503.pdf) and IRF7467 (http://www.irf.com/product-info/datasheets/data/irf7467.pdf) but none of the suppliers have CPH3442 and IRF7467 seems to be discontinued...
    Anyway - any advice...? Also - assuming that 2SK4043LS is suitable - what's the best/safest way of driving it from the MCU pin...?

    Thanks,
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Looks OK, EXCEPT:
    upload_2016-6-27_15-54-4.png
    18V @4A can't be run DC. You are limited to about 100 ms on times for a single pulse. Don't know the duty cycle.

    John
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Quite a few logic level Mosfets by IR/Vishay etc that should do it IRL series.
    Max.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    The 2SK4043LS will be fine as long as you are using it as a switch for the 18V, 4A load.
    The safe-area chart limitation that John posted is only a problem if you simultaneously have both 18V and 4A at the transistor for more that 100ms.
    For normally switching times, the maximum power dissipation occurs for less than a microsecond.
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    Another parameter of interest is the Vgs(th) or threshold voltage. It must be much less than the logic supply voltage or you will fail to turn the MOSFET on completely. Doing this is the road to perdition. You must ensure that the MOSFET is completely on when Vgs ≈ 3.3VDC.

    Last thing to understand is Qgs of 3.9 nC. This will slow down the switching speed, which means you will be spending time in the linear region and the device will get hot. Direct switching from the microcontroller can exacerbate this problem. Switching with a current source/sink is the usual solution.
     
    Last edited: Jun 27, 2016
    cmartinez likes this.
  6. crutschow

    Expert

    Mar 14, 2008
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    Better than looking at Vgs(th) and trying to determine how low is low enough, is to look at the Vgs voltage used to characterize the ON resistance in the MOSFET data sheet, which was a Vgs of 4V and 2.5v for the 2SK4043LS.

    upload_2016-6-27_13-59-22.png
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    A good quantitative alternative to using Vgs(th)
     
  8. daman

    Thread Starter New Member

    Jun 14, 2012
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    Thanks! I'll try that 2SK4043LS...
    @MaxHeadRoom: can you list one or two of IRL series hat could possibly do it? I've been looking at them and couldn't really find anything...
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    In D-Pak SMT there is IRLR014/24/110/120.
    In TO-220 there is IRLZ14/24/34/44/
    IRL510/520/530/540.
    Max.
     
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