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UCC23513: PWM control for motors with MOSFET

Ivan Vargas
Prodigy 65 points
Part Number: UCC23513

Tool/software:

Hi all,

We are developing a PWM controller for 24V motors and I have some questions.

 

  1. To calculate R_EXT I don't quite understand the ROH_buf parameter.
  2. I need to know if I am choosing the right Rg for the MOSFET or are there other considerations to take into account?

 

I appreciate your help in advance

Thank you very much!

  • 0
    TI__Mastermind 23196 points

    Hi Ian,

    Is R_EXT R33 or R32 in your schematic image?

    The SN74 buffer has a 40mA source current with 1V across it, which is roughly 25 ohms of output resistance (figure 5 below). You can use this as a ROH_buf estimated value.

    Your calculation of 112 is about right. The series combination of ROH_buf, R33 and R26 just need to limit the input current from 3.3V into the ~2.2V input diode to IF=~10mA. The Vf of the input diode depends on temperature, but there is a wide If tolerance to account for this variation. As long as the input current stays above 5mA and below 20mA, the device will work fine. 

    R32 is the gate resistor, and the lower value you use, the higher the switching speed and efficiency. Your might want to experiment with lower values if your switching frequency is high.

    Best regards,

    Sean