Philips TDA8567Q - Manual (Page 5)

1998 Sep 23 5
Philips Semiconductors Product specification
4
×
25 W BTL quad car radio power
amplifier
TDA8567Q
FUNCTIONAL DESCRIPTION
The TDA8567Q contains four identical amplifiers which
can be used for bridge applications. The gain of each
amplifier is fixed at 26 dB.
Mode select switch (pin 15)
•
Standby: low supply current (<100
µ
A)
•
Mute: input signal suppressed
•
Operating: normal on condition.
Since this pin has a low input current (<80
µ
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 10, 11, 13 and 14). 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 9)
D YNAMIC D ISTORTION D ETECTOR (DDD)
At the onset of clipping of one or more output stages, the
dynamic distortion detector becomes active and pin 9
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 9
is independent of the number of channels that are clipping
(see Fig.4).
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 9 is continuously LOW.
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
µ
s to determine whether the short-circuit
is still present.
Due to this duty cycle of 50
µ
s/10 ms the average current
consumption during this short-circuit condition is very low.
During this short-circuit condition, pin 9 is LOW for 10 ms
and HIGH for 50
µ
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 - WARNING
When the virtual junction temperature T
vj
reaches 145
°
C,
pin 9 goes LOW.
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.
Fig.3 Mode select switch circuitry.
handbook, halfpage
+
VP
MODE
MGD959
BZX79C/3.9V
10 k Ω
47 µ F
Fig.4 Distortion detector waveform.
handbook, halfpage
V9
0
VP
Vo
0
t
MGG155