4 Noise Coupling

The high-voltage input and fast switching of the power device and related snubber can lead to a high dv/dt switching node, which generates a large amount of noise. Other sources of high dI/dt loops or high dV/dt nodes in a HV DC-DC converter are gate drive, secondary-side rectifier, and transformer windings.

The voltage rating for the current sense pin must be considered when designing the backup flyback converter. A higher current sense (CS) voltage rating provides robustness against false CS pin triggering when operating across an ultra-wide input voltage range, and in a noisy environment.

The high dv/dt nodes must be kept small and away from quiet areas, such as the current sense circuitry, to reduce noise coupling. Poor layout can prevent the design from meeting the mechanical and electrical specifications needed to guarantee safe and predictable operation.