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UCC23513: The switching timing of the MOSFET in the UCC23513 pull-up

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Prodigy 10 points
Part Number: UCC23513

Tool/software:

This is a question about the switching timing of the MOSFET in the UCC23513 pull-up.
When does the ON resistor switch from ROH || RNMOS to ROH?

Does it switch with time? Or will it be switched by voltage?

  • 0
    TI__Genius 15856 points

    Hi,

    It is switched depending on OUT voltage. The output stage has a PMOS in parallel with an NMOS, as shown in Figure 8-1 (below). ROH is the resistance of the PMOS, and RNMOS is the resistance of the NMOS. The NMOS is initially driven with a gate voltage of 5V above the output. But when the output rises up to <5V from the rail, the pre-driver is unable to provide a full 5V to keep the NMOS ON, and the NMOS drive reduces. When the output is 2V away from the rail, the NMOS is fully pinched off, and only the PMOS is the path from OUT to Vdd. 

    Best regards,

    Sean