RCT is connected to the CT terminal via VDD. The BU42xx series features an RCT of 10Ω (typ), 9Ω (min), and 11Ω (max). For an external leak of 1µA, there will be a drop of 11V max. at the CT terminal. As a result, it will be always OFF. Therefore, please select a delay terminal threshold voltage VCTH that will not turn the device OFF.