This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Need to find a suitable N-mosfet

Other Parts Discussed in Thread: DRV8328, CSD17573Q5B, CSD18510Q5B, CSD18512Q5B, CSD18510KTT, CSD18540Q5B

Hi Team,

I would like to find a  new N-Mos here for power tools motor control part. 

I would like to use MCU+DRV8328+Mos in this system. The target power level is 18V/800W~1000W.

It will be better if it is a MOSFET with small packge and high efficiency(low Rdson)

Do you have any suitable recommendation?

Thanks

Jenson

  • Hey Jenson,

    From a BLDC perspective, when selecting a MOSFET, our major concerns are:

    1. Voltage rating (VDS): This should be able to account for maximum drain voltage with some room for safety.
    2. Drain current (ID): Be suited for the expected motor current to prevent damage.
    3. QGD: The rise/fall time of the MOSFET is dependent on QGD. Trise/fall = QGD/ Isource/sink.
    4. Gate to source threshold voltage (VGS (th)): The gate drive voltage of driver should be able to turn on the FET.

    Our EVM used CSD18536KTTT.

    I will let the FET team provide additional recommendations.

    Best,

    Akshay

  • Hello Jenson,

    Thanks for your interest in TI FETs. Please see link below to an app note that includes links to all of TI's  MOSFET technical information. Under the Tools section, you will find a link to a BLDC motor drive FET selection tool that allows the user to enter their system requirements and compare up to 3 TI FET solutions based on power loss, package and $1ku price. The tool also allows you to use parallel FETs to reduce conduction loss and spread the power dissipation in multiple packages if so desired. You will probably want to use at least a 30V FET for 18V input. Our lowest on resistance 30V FET for this type of application is the CSD17573Q5B in 5x6mm SON package. The FET used on the EVM is a 40V device in D2PAK package which is much higher cost and larger. If 40V is required, then the CSD18510Q5B is the lowest on resistance in 5x6mm SON. A lower cost 40V FET would be the CSD18512Q5B but on resistance and power loss are higher. Please let me know if you have any questions.

    https://www.ti.com/lit/an/slvafg3a/slvafg3a.pdf

    Best Regards,

    John Wallace

    TI FET Applications

  • Hi John,

    Thanks for your comments here,

    I check the CSD18510Q5B but I see continuous Drain Current is only 42A.(RθJA = 40°C/W on a 1-in2 , 2-oz Cu pad on a 0.06-in thick FR4 PCB)

    I think this is a good cooling condition, we can't achieve such a good condition in our system. Do you think that this XX will be smaller, so that it cannot meet the requirements of my system.

    Do you have any comments on this?

    Thanks!

    Jenson

  • Hi Jenson,

    The continuous drain current is calculated at Tamb = 25°C & Tj = 150°C using Rθja = 40°C/W as explained in the blog at the first link below. The PCB and Cu pad are standards on which we test all of our FETs. I'm including a second link on how TI tests and specs thermal impedance. The effective Rθja in the customer's application depends on PCB layout and stackup. With a good layout on a multilayer PCB the effective Rθja can be reduced 15°C/W to 20°C/W. I used the BLDC FET selection tool (attached) to estimate the FET power loss and make the FET recommendations. As shown in the third link, the maximum power dissipation of a 5x6mm SON package is around 3W on a multilayer PCB with a good layout. It's about 4W for the D2PAK.The tool shows estimated power loss for the CSD18510Q5B is around 1.6W per FET. The CSD18510KTT uses the same FET die in a D2PAK. Let me know if you have any questions.

    https://e2e.ti.com/blogs_/b/powerhouse/posts/understanding-mosfet-data-sheets-part-3

    https://e2e.ti.com/blogs_/b/powerhouse/posts/understanding-mosfet-data-sheets-part-6-thermal-impedance

    https://e2e.ti.com/blogs_/b/powerhouse/posts/selecting-the-right-power-mosfet-power-block-package-for-your-application

    MOTOR-DRIVE-FET-LOSS-CALC_Rev1.xlsm

    Thanks,

    John

  • Hi John,

    Thanks for your comments here,

    I want to make sure my understanding is correct. In the CSD18510Q5B data sheet, 42A is at Rθja = 40°C/W. I wonder why the FET loss is close to 3W in the case of 42A? I wonder if there is only one layer of copper in this test?
    According to the calculation of motor control excel, the power loss is about 1.6W, which means that if Rθja = 40°C/W, the temperature rise is only 64°C. Is it right?
    In addition, how do I know the Rθja of the PCB I have drawn?

    Thanks!

    Jenson

  • Hi Jenson,

    The max power dissipation in the datasheet is calculated: PDmax = (TJmax - Tamb)/Rθja = (150°C - 25°C)/(40°C/W) = 3.1W. This is reduced at elevated temperature. The thermal resistance (j-c and j-a) is measured on standard, single layer board with the min and max PCB pad areas as shown in the datasheet. Yes, if Rθja = 40°C/W, then ΔTj = 1.6W x 40°C/W = 64°C. Please take a look at DRV8305EVM at the link below for a good example of a PCB layout using TI FETs in 5x6mm SON packages. The EVM uses the CSD18540Q5B 60V, 1.8mΩ N-channel FET in a 3-phase BLDC motor drive application. You can download the design documents at the second link below.

    https://www.ti.com/tool/BOOSTXL-DRV8305EVM

    https://www.ti.com/lit/zip/slvc626

    Best Regards,

    John