Rds(on) graph in MOSFET data sheet

Discussion in 'General Electronics Chat' started by strantor, Sep 25, 2011.

  1. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    I'm looking at the IRFP4110PbF datasheet and trying to figure out what my Rds(on) will be @ a junction temp of 120C. The "rated" typical value is 3.7mΩ and the "max" is 4.5mΩ, but when I look at the graph, 120C corresponds to about 1.75. That makes me think it is a multiplier, but if I multiply 3.7 * 1.75 I get 6.5mΩ. so what gives?
     
  2. Pencil

    Active Member

    Dec 8, 2009
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    I am just guessing, but my observation is that
    the Rds On Typ and Max are given at Tj=25C,
    and the graph passes through 1 at what looks to
    be 25C. This supports your theory of the value
    being a multiplier. The Rds ON of a MOSFET
    increases with temperature, this is a characteristic
    of MOSFETS that makes them ideal for paralleling to
    share current, it helps to prevent thermal runaway
    and "current hogging".

    Just my observation.
     
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  3. vrainom

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    Sep 8, 2011
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    The typical and max value variation is from one device to another, measured at 25ºC. One device can have an Rds on of 3.7mΩ and the next one as high as 4.5mΩ at 25º but those values go up with temperature.
     
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  4. strantor

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    Right, but go up to what; is what I'm trying to figure out.
    If 4.5 is worst case then I assume, according to the graph, that figure would be multiplied by 1.75 for a Rds(on) of 7.87mΩ. do you concur?
     
  5. vrainom

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    Sep 8, 2011
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  6. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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