MOSFETs meet Class D audio amplifier needs

28th June 2006

ES Admin

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A new generation of trench MOSFETs from Zetex Semiconductors has been introduced to provide the high efficiency, cool running and quality audio reproduction demanded by Class D output stages. Rated at 70V, and offered in SOT223 and DPAK packages, these N- and P-channel devices ensure reliable, safe operation in higher power audio applications including flat panel TV and 5.1 surround sound systems. The selection will suit single-ended and bridge-tied-load output stages using either complimentary or all N-channel MOSFET configurations.

The higher drain-source voltage of the ZXM N/P 7 series MOSFETs offers designers extra headroom, when compared to the alternative 60V parts, which serves to accommodate any significant variation in supply and gate ringing. Their low on-resistances, typically 130m? at 10V for the N-channel and 160m? at 10V for the P-channel, means losses are kept low ensuring high efficiency operation and cool running.

The MOSFETs’ low RDS(on) combined with fast switching and low gate charge characteristics enable output stage efficiency to be optimised, to more than 90% in well-designed circuits. Turn-off time and gate drain charge for the N- and P-channel devices when operating at 10V, are specified as 17ns / 1.8nC and 35ns / 3.6nC respectively.

Handling a high drain current, the MOSFETs are able to achieve maximum power delivery for single FET operation, while the low gate drive requirement also means paralleling of FETs is possible in applications where higher power levels are demanded by the load. Maximum drain currents for SOT223 and DPAK packages are 3.8 and 6.1 Amps for N-channel types and 3.7 and 5.7 Amps for P-channel types.