TDA7374

Output stage

13/19

3.4

Built-in protection systems

3.4.1

Full protection of device and loudspeakers against AC/DC short

Reliable and safe operation in presence of all kinds of short circuit involving the outputs is

assured by a built-in protection system that operates in the following way:

In case of overload, a SCR is activated as soon as the current flowing through the output

transistors overcomes a preset threshold value depending on the chip temperature. The

SCR causes an interruption of the supply current of the power transistor.

3.4.2

Load dump voltage surge

The TDA7374 has a circuit which enables it to withstand a voltage pulse train on pins 3 and

13, of the type shown in Figure 20. If the supply voltage peaks to more than 50V, then an LC

filter must be inserted between the supply and pins 3 and 13, in order to assure that the

pulses at pins 3 and 13 will be held within the limits shown.

A suggested LC network is shown in Figure 19. With this network, a train of pulses with

amplitude up to 120 V and width of 2ms can be applied at point A. This type of protection is

ON when the supply voltage (pulse or DC) exceeds 18 V. For this reason the maximum

operating supply voltage is 18 V.

Figure 19.

A suggested LC network

Figure 20.

Voltage pulse train on pins 3 and 13

3.4.3

Polarity inversion

High current (up to 10 A) can be handled by the device with no damage for a longer period

than the blow-out time of a quick 2 A fuse (normally connected in series with the supply).

This features is added to avoid destruction, if during fitting to the car, a mistake on the

connection of the supply is made.