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CSD87501L: Driving Two N Channel MOSFET with Common Drain

Ali Movahedi
Intellectual 840 points
Part Number: CSD87501L

Tool/software:

Dear all,

I am planning to use CSD87501L in my design.  I had a quick question please.  Can I connect Gate 1 and Gate 2 together and turning both transistors ON by a GPIO from MSP430, please?

Thanks, fin advance for your reply,

A.Tesla.

  • 0
    TI__Mastermind 35520 points

    Hello Ali,

    Thanks for your interest in TI FETs. Driving the gates directly from a GPIO from MSP430 is probably not going to work. In most applications, the source of one FET is connected to a DC voltage and the source of the other FET is connected to the load. The gate of each FET must be driven at least 4.5V higher than its source to guarantee the on resistance of the FET. For example, if the DC input voltage is 12V, then the gate must be driven to at least 16.5V to guarantee the FET is on. The gates can be tied together as long as both Vg1s1 & Vg2s2 >=4.5V. Common applications for this device include USB-C power path switch and battery protection and the control IC normally includes a charge pump to generate the required gate drive voltage. Please let me know if you have any additional questions.

    Best Regards,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    Intellectual 840 points

    Dear John,

    Thank you for very well explained.  Yes, I have an additional question please.  I am connecting one end of the FET (source) to a Battery with nominal Voltage of 3.8V and the other source to a load.  If I connect Gate1 and Gate 2 together, how would I be able to charge and discharge the battery please.  Is not normally the current flowing from Drain to Source. Under what circumstance the current would flow from Source to Drain.

    Thanks, Ali.

  • 0 in reply to Ali Movahedi
    TI__Mastermind 35520 points

    Hi Ali,

    You will have to drive the gate of each FET independently to control charge and discharge. Current can flow in either direction thru the channel when the FET is on (i.e. VGS > 4.5V), When the FET is off, current can flow thru the body diode if it becomes forward biased. When both FETs are off, no current can flow because the body diodes of the two FETs are back-to-back and will block current in either direction.

    Thanks,

    John

  • 0 in reply to John Wallace1
    Intellectual 840 points

    Dear John,

    I thought in the N Channel MOSFET the current can not go in each direction (going from source to drain and vise versa) since the substrate is attached to the source?

    Warm Regards,

    ALi.

  • 0 in reply to Ali Movahedi
    TI__Mastermind 35520 points

    Hi Ali,

    When the N-channel FET is on, current can flow either direction thru the channel. When the FET is off the body diode blocks current flow from drain-to-source but if the source voltage is higher than the drain, the body diode will be forward biased and current will flow from source-to-drain.

    Thanks,

    John

  • 0 in reply to John Wallace1
    Intellectual 840 points

    Dear John,  Just one more question, please.  Would you introduce a driver that drive the gate of CSD87501L, please.

    Thanks, Ali.

  • +1 in reply to Ali Movahedi
    TI__Mastermind 35520 points

    Hi Ali,

    I am not aware of a gate driver specifically for a dual common drain FET. In most applications, this device is paired with a battery management IC or a USB-C controller that includes a charge pump and integrated gate drivers. Since this is a battery powered application, have you considered a TI battery management/charger solution? Alternatively, if you have 12V available on your board, you may be able to use a TI gate driver. I'm the applications engineer for TI's discrete and power block FETs but can reassign this thread to another applications team. Let me know if you would like me to assign this to our high performance drivers team or battery management team.

    Thanks,

    John