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UCC5310: input driving clarifications

Matteo Rigamonti
Expert 1170 points
Part Number: UCC5310

Hello,

I need a clarification about the input driving of the UCC5310M.

On paragraph 10.3.2 of datasheet I can read: "If any of the inputs are left open, 128 kΩ of internal pulldown resistance forces the IN+ pin low and 128 kΩ of internal resistance pulls IN– high. However, TI still recommends grounding an input or tying to VCC1 if it is not being used for improved noise immunity."

Accordingly to such sentence, the application example in paragraph 11.2 is:


Where I expect OUT goes to high when PWM signal goes to high.

But the functional table in paragraph 10.4 is:


With internall pull-up and pull-down resistors IN+ is normally tied to low and IN- is normally tied to high, so in the application schema above it seems impossible for the OUT to goes high.

Is that correct or am I misunderstanding anything?

Thank you in advance for any clarification

Best regards

Matteo

 

  • 0
    Guru 243180 points

    When the PWM input is low, IN+ is low, so the output is low.
    When the PWM input is high, IN+ is high, and IN− is low, so the output is high.

    The pull-up/-down resistors do not matter in this circuit because the connections to PWM or ground are much stronger. Neither input is left open.

  • 0
    TI__Intellectual 2805 points
    Thank you Clemens for jumping in and answering this post.

    I agree with Clemens here. The internal pull-up and pull-down resistors do not affect the state as much as the PWM signal.
    This internal structure ensures the UCC53x0 family is in a known state when the inputs are left open. (It is recommended to ground or tie the input to VCC1 if it is not being used, use table 5 to determine which)

    Let me know if you have any other questions!
    If you have a new unrelated question, please post another e2e thread.

    Regards,
    Mateo
  • 0 in reply to Mateo Begue
    Expert 1170 points

    Thank you to everybody for your confirmations.

    Best regards

    Matteo