STCMB1 datasheet(41/59 Pages) STMICROELECTRONICS

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STCMB1

Application information

Figure 23. Adaptive deadtime: principle schematic (left) and relevant timing diagrams (right)

Figure 24. Detail of deadtime during low-to-high transition of HB midpoint

Finally, it is worth stating that the adaptive deadtime function does not significantly increase

efficiency by itself. It is a degree of freedom that has to be exploited to this purpose when

designing the resonant tank. Essentially, it allows the use of a higher magnetizing

inductance in the transformer, which minimizes the magnetizing current and, then, the

conduction losses associated to it. Additionally, this may reduce the switched current IS to

the minimum required to achieve soft-switching, thus reducing turn-off switching losses in

MOSFETs. Efficiency at the medium and light-load will maximally benefit from this

optimization.

7.22

HB: hard switching prevention (HSP) and anti-capacitive

mode protection (ACP)

Resonant converters work in the capacitive mode when their switching frequency falls below

a critical value that depends on the loading conditions and the input-to-output voltage ratio.

They are especially prone to run into the capacitive mode when the input voltage is lower

than the minimum specified and/or the output is overloaded or short-circuited. Designing

a converter so that it never works in the capacitive mode, even under abnormal operating

conditions, is definitely possible but this might pose unacceptable design constraints in

some cases (e.g.: a transformer magnetizing current too big to comply with light-load

efficiency targets).

STCMB1 Datasheet(PDF) 41 Page - STMicroelectronics