ZHCSNG6 November 2021 UCC28781-Q1
PRODUCTION DATA
Due to different capacitance non-linearity between Si and GaN power FETs as well as different propagation delays of their drivers, the SET pin is provided to program critical parameters of UCC28781-Q1 for the two different power stages.
Firstly, this pin sets the zero-voltage threshold (VTH(SWS)) at the SWS input pin to be one of two different auto-tuning targets for ZVS control. When SET pin is tied to AGND, VTH(SWS) is set at its low level of 4 V for realizing full ZVS, which allows the low-side switch (QL) to be turned on when the switch-node voltage drops close to 0 V. When SET pin is tied to REF pin, VTH(SWS) is set at 8.5 V for implementing partial ZVS, which makes QL turn on at around 8.5 V.
Secondly, the SET pin also selects the current-sense leading-edge blanking time (tCSLEB) to accommodate different delays of the gate drivers; 110 ns for VSET = 0 V and 190 ns for VSET = 5 V.
Thirdly, the minimum PWML on-time (tON(MIN)) in low-power mode and standby-power mode is 110 ns for VSET = 0 V, and is 100 ns for VSET = 5 V.
Finally, the maximum PWML on-time to detect CS pin fault (tCSF) is adjusted. tCSF for VSET = 5 V (tCSF1) is set at 2 μs. tCSF for VSET = 0 V (tCSF0) depends on the value of RRDM. tCSF0 is configured to 2 μs when RRDM ≥ RRDM(TH) and to 1 μs when RRDM < RRDM(TH).