Circuit description

TDA7293

8/21

Doc ID 6744 Rev 8

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

behaviour 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.

3.2

Protection

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

protection of the device from short circuit or overload conditions. Due to the absence of the

2nd breakdown phenomenon, 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.

In addition to the overload protection described above, the device features a thermal

shutdown circuit which initially puts the device into a muting state (@ T

ϕ = 150 °C) and then

into stand-by (@ Tj = 160 °C).

Full protection against electrostatic discharges on very pin is included.

3.3

Other Features

The device is provided with both standby and mute functions, independently driven by two

CMOS logic compatible input pins.

The circuits dedicated to the switching on and off of the amplifier have been carefully

optimized to avoid any kind of uncontrolled audible transient at the output.

The sequence that we recommend during the on/off transients is shown in Figure 8. The

application of figure 9 shows the possibility of sing only one command for both st-by and

mute functions. On both the pins, the maximum applicable range corresponds to the

operating supply voltage.