• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 214 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

CSD86356Q5D: CSD86356Q5D

Esteban Montes
Prodigy 10 points
Part Number: CSD86356Q5D
Other Parts Discussed in Thread: LM393

Tool/software:

Hello. 

I have a circuit I have been working on to act as a low-voltage cutoff for a 21V battery to cut the power to the tool once the battery output is 16V. I am using a LM393 comparator to send the signal to the mosfet's gate and allow the current to flow through to the tool. I don't have much experience with mosfets and so I do not know what exactly to look for to pick the proper one or this application. I ordered a variety pack from amazon but none of the mosfets in that pack are able to do the job at 21V. If someone could help me understand what I need to look for it would be greatly appreciated. Thank you. 

  • 0
    TI__Mastermind 38200 points

    Hello Esteban,

    Thanks for your interest in TI FETs. From your description, it sounds like the FET is being used as a high side switch to connect the battery to the tool during normal operation and to disconnect when the battery voltage reaches the cutoff voltage of 16V. In this configuration, the drain is connected to the battery and the source is connected to the tool. Is this correct? In this application, the gate voltage must be driven higher than the battery voltage by the minimum value of VGS where Rds(on) is specified in the MOSFET datasheet. When the FET turns on, drain and source are at approximately the same voltage and the gate must be driven higher.

    Basic FET selection uses voltages (VDS & VGS), current (ID) and package to narrow down the choices. Does the FET have to block current in both directions? This may occur when the FET is supposed to be off but the source voltage exceeds the drain voltage causing the body diode to conduct when it is forward biased. If this is the case, then you would want to use back-to-back FETs in an anti-series configuration to block the current.  For a 21V you will need to use a 25V - 30V FET. How much current does the FET need to conduct when it is on? How are you going to drive the gate of the FET?

    I'm including a link below to an app note that has links to all of TI's MOSFET web based technical information including FET selection and tools for FET selection. The Excel-based load switch tool allows you to input your requirements and compare up to 3 different TI FET solutions. Please review and let me know if you have any difficulties.

    https://www.ti.com/lit/an/slvafg3f/slvafg3f.pdf

    Best Regards,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    TI__Mastermind 38200 points

    Hello Esteban,

    Following up to see if your issue has been resolved. Please let me know.

    Best Regards,

    John

  • 0 in reply to John Wallace1
    TI__Mastermind 38200 points

    Hello Esteban,

    Since I have not gotten a response from you, I assume your issue has been resolved and will close this thread.

    Best Regards,

    John