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Philips Semiconductors
4
40 W BTL quad car radio power
amplifier
FUNCTIONAL DESCRIPTION
The TDA8571J contains four identical amplifiers which can
be used for bridge applications. The gain of each amplifier
is fixed at 34 dB.
Mode select switch (pin MODE)
Standby: low supply current (<100 A)
Mute: input signal suppressed
Operating: normal on condition.
Since this pin has a low input current (<80 A), a low cost
supply switch can be applied.
To avoid switch-on plops, it is advised to keep the amplifier
in the mute mode during 150 ms (charging of the input
capacitors at pins IN1, IN2, IN3 and IN4. When switching
from standby to mute, the slope should be at least 18 V/s.
This can be realized by:
Microprocessor control
External timing circuit (see Fig.3).
Diagnostic output (pin V
D
D
D
YNAMIC
ISTORTION
ETECTOR
At the onset of clipping of one or more output stages, the
dynamic distortion detector becomes active and pin V
goes LOW. This information can be used to drive a sound
processor or DC volume control to attenuate the input
signal and so limit the distortion. The output level of
pin V
is independent of the number of channels that
DIAG
are clipping (see Fig.4).
V P
handbook, halfpage
Fig.3 Mode select switch circuitry.
2002 Mar 05
)
DIAG
(DDD)
10 k
MODE
47 F
BZX79C/3.9V
MGD959
S
-
HORT
CIRCUIT DIAGNOSTIC
When a short-circuit occurs at one or more outputs to
ground or to the supply voltage, the output stages are
switched off until the short-circuit is removed and the
device is switched on again, with a delay of approximately
10 ms after removal of the short-circuit. During this
short-circuit condition, pin V
When a short-circuit occurs across the load of one or more
channels, the output stages are switched off during
approximately 10 ms. After that time it is checked during
approximately 50 s to determine whether the short-circuit
is still present. Due to this duty cycle of 50 s/10 ms the
average current consumption during this short-circuit
condition is very low.
During this short-circuit condition, pin V
10 ms and HIGH for 50 s (see Fig.5). The protection
circuits of all channels are coupled. This means that if a
short-circuit condition occurs in one of the channels, all
channels are switched off. Consequently, the power
dissipation in any short-circuit condition is very low.
T
EMPERATURE PRE
When the virtual junction temperature T
pin V
goes LOW.
DIAG
DIAG
O
-
PEN
COLLECTOR OUTPUTS
The diagnostic pin has an open-collector output, so more
devices can be tied together. An external pull-up resistor is
needed.
V o
handbook, halfpage
0
V 9
V P
0
Fig.4 Distortion detector waveform.
5
Product specification
TDA8571J
is continuously LOW.
DIAG
DIAG
-
WARNING
reaches 145 C,
vj
is LOW for
MGG155
t
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