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TDA7294S

This large-signal, high-power buffer must be capable of handling extremely high current and voltage levels

while maintaining acceptably low harmonic distortion and good behaviour over frequency response; more-

over, an accurate control of quiescent current is required.

A local linearizing feedback, provided by differential amplifier A, is used to fullfil the above requirements,

allowing a simple and effective quiescent current setting.

Proper biasing of the power output transistors alone is however not enough to guarantee the absence of

crossover distortion.

While a linearization of the DC transfer characteristic of the stage is obtained, the dynamic be-haviour of

the system must be taken into account. A significant aid in keeping the distortion contributed by the final

stage as low as possible is provided by the compensation scheme, which exploits the direct connection of

the Miller capacitor at the amplifier’s output to introduce a local AC feedback path enclosing the output

stage itself.

4.2 Protections

In designing a power IC, particular attention must be reserved to the circuits devoted to protection of the

the SOA of the power DMOS transistors is delimited only by a maximum dissipation curve dependent on

the duration of the applied stimulus.

In order to fully exploit the capabilities of the power transistors, the protection scheme implemented in this

device combines a conventional SOA protection circuit with a novel local temperature sensing technique

which " dynamically" controls the maximum dissipation.

Figure 6. Principle Schematic of a DMOS unity-gain buffer.

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