TDA7374 datasheet(8/13 Pages) STMICROELECTRONICS

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Offset Control

The quiescent output voltage must be as close as

possible to its nominal value, so that less undis-

torted power would be available.

For this reason an input bias current compensa-

tion is implemented to riduce the voltage drop

across the input resistors, which appears ampli-

fied at the outputs.

Gain Internally Fixed to 26dB

Advantages of this design choice are in terms of:

components and space saving

output noise, supply voltage rejection and dis-

tortion optimization.

Silent Turn On/Off and Muting/Stand-by Func-

tion

The stand-by can be easily activated by means of

a CMOS level applied to pin 7 through a RC filter.

Under stand-by condition the device is turned off

completely (supply current= 1

µA TYP ; output at-

tenuation= 90 dB TYP).

Every ON/OFF operation is virtually pop free.

Furthermore, at turn-on the device stays in muting

condition for a time determined by the value as-

signed to the SVR capacitor (T= Csvr * 7,000).

While in muting the device outputs becomes in-

sensitive to any kinds of signal that may be pre-

sent at the input terminals. In other words every

transient coming from previous stages produces

no unpleasant acoustic effect to the speakers.

Another situation under which the device is totally

muted is whenever the supply voltage drops

lower than 7V. This is helpful to pop suppression

during the turn-off by battery switch.

BUILT-IN PROTECTION SYSTEMS

Full Protection of Device and Loudspeakers

Against AC/DC Short Circuits (to Gnd, to Vs,

across the Speakers).

Reliable and safe operation in presence of all

kinds of short circuit involving the outputs is as-

sured 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 transis-

tors overcomes a preset threshold value depend-

ing on the chip temperature. The SCR causes an

interruption of the supply current of the power

transistor.

Load Dump Voltage Surge

The TDA 7374 has a circuit which enables it to

withstand a voltage pulse train on pins 3 and 13,

of the type shown in fig. 16.

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 fig. 15.

With this network, a train of pulses with amplitude

up to 120V and width of 2ms can be applied at

point A. This type of protection is ON when the

supply voltage (pulse or DC) exceeds 18V. For

this reason the maximum operating supply volt-

age is 18V.

Polarity Inversion

High current (up to 10A) can be handled by the

device with no damage for a longer period than

the blow-out time of a quick 2A fuse (normally

connected in series with the supply). This fea-

tures is added to avoid destruction, if during fitting

to the car, a mistake on the connection of the

supply is made.

Open Ground

When the radio is in the ON condition and the

ground is accidentally opened, a standard audio

amplifier will be damaged. On the TDA7374B pro-

tection diodes are included to avoid any damage.

Inductive Load

A protection diode is provided to allow use of the

TDA7374B with inductive loads.

Figure 15

Figure 16

TDA7374B

8/13

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