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Recommend TI MOSFETs to relace with AO3400 and wsf40n06

Jiandong Liu
Intellectual 1801 points
Other Parts Discussed in Thread: CSD18543Q3A, CSD17585F5, CSD18537NQ5A, CSD18514Q5A

AO3400 is used as the load switch to control a fan, which must have 2A, 24V capacity;

wsf40n06 is used as the load switch to control the heating resistor, which must have 20A, 24V capacity;

The expected volume of these MOSFETs are quite large, so could you give me some advices with lowest cost?

  • 0
    TI__Mastermind 38190 points

    Hi Jiandong,

    Thanks for promoting TI FETs. AO3400 is in a SOT23 package and we don't make any FETs in this package. As an alternative, I would recommend CSD17585F5 FemtoFET. The wsf40n06 is in a DPAK which we also don't make. As an alternative, I would recommend CSD18537NQ5A in 5x6mm QFN or CSD18543Q3A in 3x3mm QFN. Both are lower rds(on) than the competition.

  • 0 in reply to John Wallace1
    TI__Intellectual 1801 points

    Hi John,

    Thanks for your recommendation.

    The first figure is  from wsf40n06 datasheet, the second one is from  CSD18543Q3A.

    When we compare these two devices, which parameters should we focus?

    And the customer required the heating current is abbout 20A, but I'm not sure about which parameter indicate this requirment? Both for TI and WINSOK device.

    By the way, is CSD18514Q5A also a good choice? Considering the MOSFET only works at 24V condition.

  • 0 in reply to John Wallace1
    TI__Intellectual 1801 points

    Also, compared with SOT23 or DPAK, does FemtoFET and QFN package have any selling points?

  • 0 in reply to Jiandong Liu
    TI__Mastermind 38190 points

    Hi Jiandong,

    Let's start with current ratings. The numbers in the datasheet are usually calculated based on thermal impedance and on resistance. Is the heating current of 20A continuous or is it pulsed? If it is pulsed, what is the pulse width and duty cycle? If it is pulsed, then we need to use the transient thermal impedance curves in the datasheet to determine if the FET can handle the current. A 5x6mm QFN (or as TI calls it SON) package can dissipated a maximum of about 3W with a good layout and depends on ambient temperature and airflow (if there is any). The QFN includes a large thermal drain pad on the backside of the package which can be used to dissipate heat into the PCB. The FemtoFET is a family of LGA parts in very small packages and is much smaller than a SOT23. It can dissipate about 0.5W maximum with a good layout. For more information, please check here: .

    Please check this blog:

    Understanding MOSFET data sheets, Part 3 - Continuous current ratings
    Welcome back, fellow FET enthusiasts to part three of the " Understanding MOSFET Data Sheets " blog series! Today I’ll be talking about MOSFET current ratings and how they’re not real. Ok, so maybe a better…
    By in Technical articles > Power management
    .

    The CSD18514Q5A may work for the heating application. Of course, it is a 40V BVDSS and that usually means a larger die size than a 30V FET for the same rds(on). The maximum power dissipation with VGS = 10V and Tcase = 25C: PD = I2 x rds(on) = (20A)(20A) x 4.9mOhm = 1.96W. The on resistance increases with temperature (see Figure 8 in the datasheet) so at Tcase = 100C, the dissipated is multiplied by 1.5 or 2.94W. This is pushing the limits of what the 5x6 QFN package can dissipate. Please review and let me know if you have any additional questions. There is a 6 part blog series for understand MOSFET datasheets here: e2e.ti.com/.../MOSFET+Blog+Series

  • 0 in reply to John Wallace1
    TI__Intellectual 1801 points

    Hi John,

    Thanks very much for your supporting.

    Best regards.

    Jiandong LIU

  • 0 in reply to Jiandong Liu
    TI__Mastermind 38190 points

    Hi Jiandong,

    Thanks again for promoting TI FETs at your customers. I am going to close out this thread and we can continue our discussion on regular email.