SLUSDO2C June 2020 – February 2021 UCC21540-Q1
The UCC21540-Q1 output stage features a pull-up structure which delivers the highest peak-source current when it is most needed: during the Miller plateau region of the power-switch turn on transition (when the power switch drain or collector voltage experiences dV/dt). The output stage pull-up structure features a P-channel MOSFET and an additional pull-up N-channel MOSFET in parallel. The function of the N-channel MOSFET is to provide a boost in the peak-sourcing current, enabling fast turn on. This is accomplished by briefly turning on the N-channel MOSFET during a narrow instant when the output is changing states from low to high.
The ROH parameter is a DC measurement and it is representative of the on-resistance of the P-channel device only. This is because the pull-up N-channel device is held in the off state in DC condition and is turned on only for a brief instant when the output is changing states from low to high. Therefore the effective resistance of the UCC21540-Q1 pull-up stage during this brief turn-on phase is much lower than what is represented by the ROH parameter.
The pull-down structure of the UCC21540-Q1 is composed of an N-channel MOSFET. The ROL parameter, which is also a DC measurement, is representative of the impedance of the pull-down state in the device. The output voltage swings between VDD and VSS for rail-to-rail operation.