width considerations for MOSFET switch

Discussion in 'General Electronics Chat' started by arunkps, Feb 12, 2014.

  1. arunkps

    Thread Starter New Member

    Jan 28, 2014
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    What are the Width Length design considerations for the switch MOSFET (PMOS or NMOS) in synchronous buck converter?
     
  2. pwdixon

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    Oct 11, 2012
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    Odd question. Are you really asking about the physical size of the device?
     
  3. tshuck

    Well-Known Member

    Oct 18, 2012
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    ...or are you referring to the channel dimensions used in the semiconductor?
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    or maybe PCB trace/track width/length considerations?
     
    tshuck likes this.
  5. ScottWang

    Moderator

    Aug 23, 2012
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    Probably you are asking about the heat sink for the MOSFET, if the answer is yes then what are the W/V/I?
     
  6. mcgyvr

    AAC Fanatic!

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    "size doesn't matter" :)
     
  7. GopherT

    AAC Fanatic!

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    It's funny that the big MOSFETS never say that, just the small ones.
     
  8. pwdixon

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    Oct 11, 2012
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    Nice to see the originator of this thread hasn't even bothered to come back and ask a sensible question.
     
  9. ScottWang

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    Aug 23, 2012
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    Why you said that nice to see the OP ...
     
  10. pwdixon

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    Ironic .
     
  11. arunkps

    Thread Starter New Member

    Jan 28, 2014
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    Hi,

    Sorry, for the delay and it is because of my internet problem. Meanwhile, people presumed about my absence.

    Ok, here I give the detail. Basically I am designing a synchronous buck converter and have planned to do a layout in 180nm in Cadence. Initially, when I simulated a simple buck converter power stage in Cadence, I faced problem in the switching section i.e., both HSS (High Side Switch) and LSS (Low Side Switch). So when I tried to simulate a MOSFET (PMOS or NMOS) alone, I noticed that the MOSFET not acting as switch until I increased the width of the MOSFET to enormous value (100um). It is my understanding from the simulations; that inorder to act the MOSFET as switch, the width should be made very large such that the ON resistance become very small and the VDS ON will be very less and the complete input voltage can be seen at the output of the MOSFET.
    My simulations files are there for your reference. However the simulations are of the asynchronous buck converter.

    The designed component values are for the spec
    vin=1.8v
    vout=500mv
    Load current=1mA
    switching frequency=1MHz
    output Iripple=100uA
    Output Vripple=500uv

    Please help me in simulating this power stage.
     
  12. arunkps

    Thread Starter New Member

    Jan 28, 2014
    16
    0
    Hi,

    Sorry, for the delay and it is because of my internet problem. Meanwhile, people presumed about my absence.

    Ok, here I give the detail. Basically I am designing a synchronous buck converter and have planned to do a layout in 180nm in Cadence. Initially, when I simulated a simple buck converter power stage in Cadence, I faced problem in the switching section i.e., both HSS (High Side Switch) and LSS (Low Side Switch). So when I tried to simulate a MOSFET (PMOS or NMOS) alone, I noticed that the MOSFET not acting as switch until I increased the width of the MOSFET to enormous value (1000um). It is my understanding from the simulations; that in order to act the MOSFET as switch, the width should be made very large such that the ON resistance become very small and the VDS ON will be very less and the complete input voltage can be seen at the output of the MOSFET.
    My simulations files are there for your reference. However the simulations are of the asynchronous buck converter.

    The designed component values are for the spec
    vin=1.8v
    vout=500mv
    Load current=1mA
    switching frequency=1MHz
    output Iripple=100uA
    Output Vripple=500uv

    Please help me in simulating this power stage.
     
  13. crutschow

    Expert

    Mar 14, 2008
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    What type of help do you need with the simulation?
     
  14. arunkps

    Thread Starter New Member

    Jan 28, 2014
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    0
    I am not getting the desired 500mv output voltage.
     
  15. crutschow

    Expert

    Mar 14, 2008
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    Output voltage on which schematic? Show us the voltages at all the nodes.
     
  16. arunkps

    Thread Starter New Member

    Jan 28, 2014
    16
    0
    Hi,

    Attachment in the buck converter circuit. I have designed the component values to get Vo of 500 mv. I will be thankful, if you can simulate it in 180nm (preferably CADENCE).
     
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