Friday, July 11, 2008

Supertex Class-D driver for high power audio amplifiers

Californian high voltage chip firm Supertex has introduced a Class-D driver for high power audio amplifiers.

"The MD7120 has been optimised for parameters critical to Class-D audio performance such as high efficiency and low EMI," said marketing v-p Ahmed Masood.

"Additionally, this Mosfet driver provides up to a 3.A peak driving current with matched output resistance and channel-to-channel propagation delay for lower total harmonic distortion and noise."

Powered from between 200V and 12V, amplifiers can be built with over 100W output with 90 per cent efficiency.

Dead time matching is ±5ns with rise or fall times under 30ns into a typical 1nF load. Four N-channel output mosfets are required, driven from normal logic level inputs by directly coupled internal level translators.

On-chip is control logic, level translators, a bootstrap-powered high side gate driver and over-temperature, under-voltage and current protection circuits.

"The thresholds of the current protection for both the high and low sides are resistor-programmable," said Supertex.

An associated application note AN-H61 (PDF) describes demo board with a self-oscillating 750kHz second-order modulator using the driver. The board delivers 50W into 8Ω with 0.01 per cent THD+noise from ±35V. Claimed efficiency of the power stage is over 80 per cent at 10 to 20W.


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