STCMB1 datasheet(29/59 Pages) STMICROELECTRONICS

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STCMB1

Application information

Figure 14. Block diagram of the HB resonant controller in the STCMB1

A special feature of this IC is that it is able to automatically adjust TD within a range so that

it best fits the transition time of the half-bridge midpoint (adaptive deadtime). This allows the

user to optimize the design of the resonant tank so that soft-switching can be achieved with

a lower level of reactive energy (e.g.: magnetizing current), hence optimizing efficiency

under a broader load range, from full to the light-load.

To perform converter's output voltage regulation the device is able to operate in different

modes, depending on the load conditions:

Variable frequency with 50% duty cycle at the heavy and medium load. A relaxation

oscillator (see Section 7.18: HB: oscillator on page 33 for more details) generates

a sawtooth, which MOSFETs' switching is locked to. The frequency of this waveform is

regulated by:

A current that is modulated by the feedback circuitry (as in DFC systems)

A control of the amount of time elapsing from a zero crossing of the tank current to

the next switching of the half-bridge (timeshift control - TSC)

Burst mode with no or a very light-load. When the load falls below a value, the

converter enters a controlled intermittent operation, where series of a few switching

cycles at a nearly fixed frequency (bursts) are spaced out by idle periods where both

MOSFETs are in off-state. A further load decrease will be translated into shorter bursts

and longer idle periods and then into a reduction of the average switching frequency.

STCMB1 Datasheet(PDF) 29 Page - STMicroelectronics