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UCC27714: level shift inquiry

Howard Zou
Genius 12365 points
Part Number: UCC27714

Hi,

in the internal circuit for HI to HO level shift. It's two Vss/HS level shift, but I'm confused, why it has to be two Vss/HS level shift?

Is the left Vss/COM level shift, and the right side is COM/HS level shift?

Besides, could you please explain the two MOSFETs connected to the right Vss/HS level shift from HB to COM. How does it work and what's the purpose of these 2 MOSFETs?

  • 0
    TI__Guru**** 189401 points
    Hi, Howard, Ni hao! The two MOSFETs, coupled with the resistors connected to their drains are what is doing the physical level shifting. I’ll ask Richard to explain the other blocks next week when he is back in the office.
  • 0
    TI__Mastermind 23135 points

    Hello Howard,

    I see why you ask the question. for the VSS to HS level shift there is logic that generates a pulse for the driver input rising edge and another pulse for the driver input falling edge. The open drains and pull up resistors are the level shifting method from COM to HS. The turn on pulse sets the driver in the high state and the turn off pulse sets (resets) the driver in the off state.

    Confirm if this addresses your questions or you can post additional questions on this thread.

    Regards,

  • 0 in reply to Richard Herring
    TI__Genius 12365 points

    Richard,

    sorry but my question is about the two red circle part.

    If the left side is already Vss/HS level shift, why there is another the same level shift at the right side?

    We would only need one Vss/HS level shift.

    So I guess we name it wrongly, the left side is Vss/COM level shift, and the right side is then COM/HS level shift, these two combine together achieves Vss/HS level shift.

  • 0 in reply to Howard Zou
    TI__Mastermind 23135 points

    Hello Howard,

    I believe your statement is correct on the left being the Vss to COM and the right the high voltage level shift to HS, although the FETs are part of the HS level shifter.

    Confirm if this addresses your questions, or you can post additional questions on this thread.

    Regards,