TDA7370B Datasheet, PDF (11/17 Pages) STMicroelectronics – QUAD POWER AMPLIFIER FOR CAR RADIO

TDA7370B
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 reduce the voltage drop
across the input resistors, which appears ampli-
fied at the outputs.
Gain Internally Fixed to 20dB in Single Ended,
26dB in Bridge
Advantages of this design choice are in terms of:
components and space saving
output noise, supply voltage rejection and dis-
tortion optimization.
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. The normal working is restored by a re-
start circuit going into action as soon as the short
circuit is removed.
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 unpleasantacoustic 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.
Load Dump Voltage Surge
The TDA7370B has a circuit which enables it to
withstand a voltage pulse train on pins 3 and 13,
of the type shown in fig. 22.
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. 21.
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.
Figure 21
Easy Single Ended to Bridge Transition.
The change from single ended to bridge configu-
rations is made simply by means of a short circuit
across the inputs, that is no need of further exter-
nal components.
Figure 22
High Application Flexibility
The availability of 4 independent channels makes
it possible to accomplish several kinds of applica-
tions ranging from 4 speakers stereo (F/R) to 2
speakers bridge solutions.
In case of working in single ended conditions the
polarity of the speakers driven by the inverting
amplifier must be reversed respect to those
driven by non inverting channels.
This is to avoid phase inconveniences causing
sound alterations especially during the reproduc-
tion of low frequencies.
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