The output stages of the UCC23511 family feature a pullup structure that delivers the highest peak-source current when it is most needed which is during the Miller plateau region of the power-switch turnon transition (when the power-switch drain or collector voltage experiences dV/dt). The output stage pullup 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 brief boost in the peak-sourcing current, enabling fast turnon. Fast turnon 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 on-resistance of this N-channel MOSFET (R_NMOS) is approximately 5.1 Ω when activated.

The R_OH parameter is a DC measurement and is representative of the on-resistance of the P-channel device only. This parameter is only for the P-channel device because the pullup 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 UCC23511 pullup stage during this brief turnon phase is much lower than what is represented by the R_OH parameter, yielding a faster turn on. The turnon-phase output resistance is the parallel combination R_OH || R_NMOS.

The pulldown structure in the UCC23511 is simply composed of an N-channel MOSFET. The output voltage swing between V_CC and V_EE provides rail-to-rail operation because of the MOS-out stage which delivers very low dropout.

Figure 8-4 Output Stage