SNVSB97A December 2018 – September 2021 LM34936-Q1
The output side MOSFETs QH2 and QL2 see the output voltage of 12 V and additional transient spikes at SW2 during switching. Therefore, QH2 and QL2 should be rated for 20 V or more. The gate plateau voltages of the MOSFETs should be smaller than the minimum input voltage of the converter, otherwise the MOSFETs may not fully enhance during startup or overload conditions.
The power loss in QH2 in the buck mode of operation is approximated by:
The rise (tr) and the fall (tf) times can be based on the MOSFET datasheet information or measured in the lab. Typically, a MOSFET with smaller RDSON (lower conduction loss) has longer rise and fall times (larger switching loss).
The power loss in QH2 in Boost mode of operation is shown in Equation 34: