What are the considerations when designing MOSFET gate drive for synchronous rectification switching converters?
Shoot-through current is a potential problem for MOSFETs used in synchronous rectification. Because the gate driver must turn on and off not only the power switch but also the rectifier switch, a low impedance may be presented to the input voltage source during switching transitions. This low transition impedance can allow a shoot-through current to be conducted through both the power-switching MOSFET and the synchronous-rectifier MOSFETs. High shoot-through currents result in greater electromagnetic interference, more noise on the input voltage source, lower efficiency, and reduced reliability. Some gate-driver ICs include a non-overlap circuit that prevents shoot-through current. Other ICs specify a minimum amount of nonoverlap, or dead-time. That is, a minimum time at the switching transitions (two per operating cycle) where both MOSFETs are turned off. Maintaining the dead-time prevents the problem of shoot-through current but reduces circuit efficiency from its optimum value.
