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Cutting complexity
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07/11/2008
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Industrial applications require more and more computing power, provided by dsps, fpgas, digital asics and microcontrollers. However, supply voltages are decreasing, supply currents are increasing and these devices usually require separate voltages for the core and I/O structures and precise sequencing so they will not latch up.
A solution is embedded dc/dc converters, but these must have excellent efficiency and the space available for them is small – particularly challenging for the thermal design, as embedded converters rely heavily on copper areas around the components on the pcb to improve thermal resistance. This is worsened by increasing load currents, since the power dissipated increases with the square of the current. Hence, power switches with low Rds(on) and low switching losses are required. There is, however, a trade off to be made: devices with the lowest possible Rds(on) have higher parasitic capacitances, hence switching losses, and so may cause higher power dissipation.
Another requirement is low emi. The noise generated by these converters can disturb surrounding circuitry and must be kept to a minimum. Yet, switching large currents at high speed inevitably leads to strong switching noise, both conducted and radiated. As a consequence, special care must be taken to optimise power stage component selection and layout, as well as the driver connections.
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Author
Ingrid Kugler and Alfred Hesener
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