Choosing right Gate driver for MOSFET ?

Discussion in 'Power Electronics' started by mishra87, Aug 3, 2019.

  1. mishra87

    Thread Starter Active Member

    Jan 17, 2016
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    Hi All,

    I want to drive 24V@3A dc pump using MOSFET through microcontroller.

    Now I have some confusion in gate driver selection.

    I do not know when to choose Mosfet gate driver.

    Selecting dedicated gate driver IC costing more.
    Could anybody suggest me some low cost solutions on the same.

    Regards,
     
  2. jpanhalt

    Expert

    Jan 18, 2008
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    How are your mosfets configured? Which mosfets do you plan to use?
     
  3. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
    3
    Mosfet is going to use mcu digital out pin.

    TSM900N06 I have chosen this for my application.

    Regards
     
  4. jpanhalt

    Expert

    Jan 18, 2008
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    That is an N-channel mosfet. Are you using a full-bridge, half-bridge, or just single mosfet? Will its source by ground/common or connected to the load? Please show your circuit.

    What will be the switching frequency?
     
  5. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
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    No switching frequency . it is to be driven from MCU DO at 3.3V logic level.
    e.g.
    upload_2019-8-3_17-49-39.png
     
  6. jpanhalt

    Expert

    Jan 18, 2008
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    The datasheet I found did not show performance for Vgs for less than 4.5 V. Do you have its characteristics for a gate voltage of 3.3V? If not, you will probably need to use a driver. Since you apparently are just using it as an on/off switch (i.e., switching speed is not that important), a simple level shifter to 5.0 volts may work, or find a mosfet that is characterized for your voltage.

    As with most devices, the package you use will make a difference in the power it can dissipate. So, tell us the package.
     
  7. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
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    VGS(th) = 1.2V min so i think mosfet will turn ON with 1.2V
    SO my question when i should mosfet drive

    upload_2019-8-3_18-35-7.png
     
  8. OBW0549

    Distinguished Member

    Mar 2, 2015
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    No, it will not. Read the data sheet CAREFULLY: note that it defines Vgs(th) as the gate-to-source voltage which will cause the drain current to be 250 μA. In other words, Vgs(th) is the gate voltage at which the MOSFET begins to conduct-- not the gate voltage which will allow it to conduct 3 amps, which is what you need.

    If your logic is operating at 3.3 volts, you will definitely need to use a gate driver of some sort to boost the drive voltage.
     
    shortbus likes this.
  9. crutschow

    Expert

    Mar 14, 2008
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    If your particular MOSFET has the minimum VGS(th) of 1.2V it may turn on sufficiently at 3.3V to carry the motor current, but if you happen to get one with the maximum VGS(th) of 2.5V, it won't.

    You can use an NPN BJT to level shift your 3.3V signal to a higher voltage.
    Do you have any higher voltages available besides the motor 24Vdc?
     
  10. tindel

    Well-Known Member

    Sep 16, 2012
    655
    219
    Are you in love with that transistor? There are other transistors that will do 3A all day long with a 3.3V drive. This one has an Rds on of 68mohm @ 2.5V Vgs. This would save you the expense of an additional part, and you'd get a smaller footprint than with your original transistor.

    You probably also want a resistor ~1kohms to limit the current through the micro during turn-on to an acceptable level. The gate of the transistor looks like a capacitive short when it charges. This will slow the turn-on but not to an appreciable level.

    If you need a higher power transistor (due to high temp operation/derating) here is a list of about 45 others that might fit the bill.

     
    Last edited: Aug 3, 2019
  11. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
    3
    No i have only 24Vdc and 5vdc on the board.
    could you share NPN bjt schematic for my better understanding.

    At-least i want mosfet with 4 times higher rating than rated current to avoid any stress.

    Regards,
     
  12. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
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    I do not understand mosfet is able supply 3A current at 1.2V VGS(th) and not at VGS(th)=2.5V.
     
  13. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
    3
    I am not biased with that MOSFET.

    I am free to select new part if somebody suggest good low cost part.

    Vds should be 60V and ID=11/12 with low Rds ON

    Regards
     
  14. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
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    Most of MOSFET manufacture says ID at ambient 25 degC.

    So it would be better if we choose some higher rated mosfet to provide enough headroom over temperature.

    Regards,
     
  15. bertus

    Administrator

    Apr 5, 2008
    19,787
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    Hello,

    There are also manufacturers that show the absulute maximum currents at 25 °C and 100 °C.
    Have a look at the IRL540 datasheet.

    Bertus
     
  16. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
    3
    this part pat and 36A rating over design the system as i think.

    Regards,
     
  17. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
    3
    maybe you can suggest some gate driver using discrete components to reduce bom cost.
     
  18. crutschow

    Expert

    Mar 14, 2008
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    Because a voltage of 3.3V-2.5V = 0.7V is not enough voltage over the threshold value to fully turn on the MOSFET.
    It would need a higher applied Vgs to fully turn on.
    it's the voltage above the threshold value that determines how well the MOSFET is turned on.
    Below is an example circuit that uses a NPN BJT to level translate the signal without signal inversion.

    R1 and R2 reduce the Vgs ON volage to keep it below the MOSFET maximum value (typically 20V).

    upload_2019-8-3_11-18-45.png
     
  19. mishra87

    Thread Starter Active Member

    Jan 17, 2016
    508
    3
    Still i do not agree with you on MOSFET Turn ON condition.

    VGS>VGS(th)

    So VG-VS>VGS(th)

    3.3-0V> (2.5V)
    3.3>2.5V so i assume mosfet gets fully turned ON.

    Thanks for sharing simulation results.
    Could you suggest some good mosfet rated for 11/12A ID with VDS=60V

    Regards,

    Regards,
     
  20. jpanhalt

    Expert

    Jan 18, 2008
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    If you know that to be the case, then why are you concerned about a gate driver?
     
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