TDA7385

Application hints

Doc ID 8160 Rev 6

13/17

frequency. In other words, this feature offers the means to counteract the extremely sound-

damaging effects of clipping, caused by a sudden increase of odd order harmonics and

appearance of serious inter-modulation phenomena.

Figure 16.

Clipping detection waveforms

Another possible kind of distortion control could be the setting of a maximum allowable THD

limit (e.g. 0.5%) over the entire audio frequency range. Besides offering no practical

advantages, this procedure cannot be much accurate, as the non-clipping distortion is likely

to vary over frequency.

In case of Overheating, pin 25 will signal out the junction temperature proximity to the

thermal shut-down threshold. This will typically start about 2°C before the thermal shut-

down threshold is reached.

As various kind of diagnostics information is available at pin 25 (clipping, shorts and

overheating), it may be necessary to operate some distinctions on order to treat each event

separately. This could be achieved by taking into account the intrinsically different timing of

the diagnostics output under each circumstance.

In fact, clipping will produce pulses normally much shorter than those present under faulty

conditions. An example of circuit able to distinguish between the two occurrences is shown

by Figure 18.

3.5

Stability and layout considerations

If properly layouted and hooked to standard car-radio speakers, the TDA7385 will be

intrinsically stable with no need of external compensations such as output R-C cells. Due to

the high number of channels involved, this translates into a very remarkable components

saving if compared to similar devices on the market.

To simplify pc-board layout designs, each amplifier stage has its own power ground

externally accessible (pins 2,8,18,24) and one supply voltage pin for each couple of them.

Even more important, this makes it possible to achieve the highest possible degree of

separation among the channels, with remarkable benefits in terms of cross-talk and

distortion features.

About the layout grounding, it is particularly important to connect the AC-GND capacitor (C5)

to the signal GND, as close as possible to the audio inputs ground: this will guarantee high

rejection of any common mode spurious signals.

The SVR capacitor (C6) has also to be connected to the signal GND.

Supply filtering elements (C7, C8) have naturally to be connected to the power-ground and

located as close as possible to the Vs pins.