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UCC27531: Need help validating a proposed schematic

HPB
Expert 1350 points
Part Number: UCC27531

I need to switch a N-MOSFET at 24V. The selected MOSFET is NTD5865NL. The current through the MOSFET will not exceed 5A and I'm trying to see if the UCC27531 would a good choice to drive this MOSFET. The proposed schematic is as shown below. There is a 12V zener at the EN pin to clamp it to 12V. If I've read the datasheet right, the max value at the EN and IN pins is 25V which is too close to the supply voltage for comfort. There is also a 12V zener on the gate of the MOSFET to clamp the Vgs at 12V since the supply voltage is more than the Vgs maximum permissible value. Can you please let me know if this schematic is designed right?

  • 0
    TI__Genius 13445 points

    Hello HPD, 

    Thanks for reaching out, my name is Mamadou Diallo and I will help address your inquiry.

    -Please add decoupling capacitors (1uF and 0.1uF) on pin 3. On PCB board, ensure these caps are placed directly across the pin to minimize noise.

    -You may simply tie EN to VCC through small current limiting resistance <5-Ohms and move the clamp to VCC pin or leave EN floating as it is internally pulled to Vref = 5.8V.

    -(Optional but recommended) please add small RC filter on IN pin R<=100-Ohms and C<=200pF for filtering input signal.

    -Good choice for R10 and D4, please ensure they placed closed to gate with little PCB traces.

    -Increase R4 to 1 to 5-Ohms depending on desired rise time. FET only has 29nC of total gate charge therefore no gate resistance on turn-on path will cause overshoot and EMI. You can also reduce this value if inappropriate.

    -Layout guidelines: place U1 as close as possible to Q1 to minimize PCB traces inductances and other parasitic.

    For more layout guidelines, please refer to the app note below:

    http://www.ti.com/lit/an/slua964/slua964.pdf

    Please let us know if you have further questions.

    Regards,

    -Mamadou