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UCC21732-Q1: the function of Hybrid pull-up structure

Part Number: UCC21732-Q1

Dear team,

The datasheet said that this structure is to achieve rail to rail output. Can't a single NMOS or PMOS achieve rail to rail output? At the first, the NMOS takes in charge until the output increase to VDD-3, then the PMOS takes in charge. Why NMOS don't continue to take in charge when output>VDD-3?

Thanks & Best Regards,


  • Hi Sherry,

    Welcome to E2E!

    The initial stage, when both NMOS and PMOS are active, allows to drive a higher current. Once the output reaches VDD-3V the NMOS will shutdown because it needs a VGS>3V (threshold voltage) to operate.

    Best regards,

    Andy Robles