Enhancing buck converter power density

3rd June 2015

Aimed at increasing the power density of DC-DC converters, the DMC1028UFDB complementary MOSFET pair - introduced by Diodes Incorporated - integrates an N-channel MOSFET and a P-channel MOSFET in a single DFN2020 package.

The design is customised for point-of-load (POL) converters that step down from 3.3V to 1V for core voltage supply to ASICs. Target applications are Ethernet network controllers and processors used in such equipment as routers, network interface controllers (NICs), switches, digital subscriber line (DSL) adaptors, servers, and set-top boxes (STBs).

Buck converters implemented using a separate PWM controller and external MOSFETs enhance design flexibility and provide for distributed heat dissipation from the switching elements.

The performance parameters of the DMC1028UFDB MOSFETs have been optimised to maximise efficiency in 3.3V to 1V buck converters while driving loads up to 3A. These include: a low 19mOhm Rds(on) at Vgs=3.3V for the low-side N channel MOSFET, which is mostly on for two-thirds of the switching cycle; and a low gate charge (Qg) of 5nC at Vgs=3.3V for the P channel MOSFET, to minimize switching losses.

The DMC1028UFDB uses a P channel MOSFET to implement the high-side switching element, which simplifies the design and reduces the component count compared to an N-channel MOSFET that would require a charge pump. Overall power density is doubled by combining the P-channel and N-channel devices, as a complementary MOSFET pair, in a single DFN2020 package relative to individual MOSFETs in the same footprint package.




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