maximum current supported by NPN transistor

Discussion in 'General Electronics Chat' started by azerty1, Nov 18, 2014.

  1. azerty1

    Thread Starter New Member

    Apr 30, 2013
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    hello,
    I'm working on a circuit based on bipolar transistors, and I want to know what is the maximum current "ICmax" that can support an NPN transistor in 0.35μm BiCMOS technology or that of the 0.25μm technology.
    So is that you have an idea on the value of the maximum current or a method to determine that?
    Kind regards.
     
  2. wmodavis

    Well-Known Member

    Oct 23, 2010
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    It should be found on the manufacturer's data sheet for the device. That is the first place to check.
     
  3. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Also check Save Operating Area on the datasheet.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    Since you are talking about semiconductor processes, and not specific devices, the answer depends on how big you make the transistor and what effect is limiting the max current. You want to make a transistor that can handle tens of amps, that can be done. Might be expensive, but it can be done. Individual transistors in an IC tend to have fairly low current capability, so you put lots of them in parallel (sometimes hundreds or even thousands) to get the drive string you want.
     
  5. azerty1

    Thread Starter New Member

    Apr 30, 2013
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    I do not have a data sheet for these transistors, I have only a list of parameters as Is, BF, Rc, Rb .... But I can not find an indication for ICmax.
     
  6. azerty1

    Thread Starter New Member

    Apr 30, 2013
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    I am currently worked with 3mA to simulate my circuit, I am afraid that my transistor does not support it or i have chance to worke with more than 3mA.
    So my goal is to get that value in order not to exceed it and to know the maximum current that can withstand my circuit.
    A circuit that works more than 3mA is more powerful than other walking to 900μA.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    The transistor current rating is determined by how large the transistor is (which determines it's on resistance and power dissipation) and the current rating of the metalization traces. So the current rating is determined by the physical design of the layout.
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    You generally have a maximum current density in the various layers, which includes the transistor regions themselves, but also the contacts and the metal layers.
     
  9. azerty1

    Thread Starter New Member

    Apr 30, 2013
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    for example, for the following NPN transistor parameters, what it is the ICmax:
    « .MODEL NR100N NPN
    + IS=121E-018 BF=137.5 VAF=159.4 IKF=6.974E-3 ISE=36E-16
    + NE=1.713 BR=0.7258 VAR=10.73 IKR=2.198E-3 RE=1 RB=524.6 RBM=25 RC=50
    + CJE=0.214E-12 VJE=0.5 MJE=0.28 CJC=0.983E-13 VJC=0.5 MJC=0.3 XCJC=0.034
    + CJS=0.913E-12 VJS=0.64 MJS=0.4 FC=0.5 TF=0.425E-9 TR=0.425E-8 EG=1.206
    + XTB=1.538 XTI=2
    »
     
  10. BobTPH

    Active Member

    Jun 5, 2013
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    Are you really designing an IC at the individual transistor basis?

    Bob
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    The simulation model doesn't capture things like ICmax because the model is only intended to capture the information needed to accurately model the electrical behavior of the device.

    You need to look at the physical design rules to determine operating limits.
     
  12. azerty1

    Thread Starter New Member

    Apr 30, 2013
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    WBahn, you say that "You need to look at the physical design rules to determine operating limits."
    Can you tell me more information about this topic and there are a procedure or a method for determine this current.
     
  13. WBahn

    Moderator

    Mar 31, 2012
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    Each process comes with a set of design rules for that process. This is typically a very large document, particularly in a deep-submicron process, that can be hundreds to over a thousand pages long. Worse, the quality of the documentation varies drastically and is often very unfriendly until you've spent a lot of time deciphering how they word things.

    But part of this document, one way or another, are physical device limitations that allow the designer to size their devices so that they will satisfy a certain level of reliability. There are often several limitations, perhaps due to thermal concerns or electromigration or device punch through, that have to all be satisfied simultaneously and for different devices and different circuits the limiting factor will be different.

    Do you have the design rules for this process? These can be pretty hard to get your hands on unless you are registered with that fab and have signed all the non-disclosure agreements. But for some processes it is much easier to get this info, particularly for schools.
     
  14. azerty1

    Thread Starter New Member

    Apr 30, 2013
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    ok, thank you very much for your help.
     
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