2002 Jan 14
7
Philips Semiconductors
Preliminary specification
4
×
44 W into 4
Ω
or 4
×
75 W into 2
Ω
quad BTL car radio power amplifier
TDA8591J
7
FUNCTIONAL DESCRIPTION
The TDA8591J is an audio power amplifier with four
independent Bridge Tied Load (BTL) amplifiers with high
output power and low distortion. The gain of each amplifier
is fixed at 26 dB. The TDA8591J has two-pin mode control
which allows the amplifiers to be switched to standby (off)
with the STBY pin, and the MUTE/ON pin to be used to
switch between mute mode (input signal suppressed) and
amplifier operating mode.
Special attention is paid to dynamic behaviour:
•
A fast mute that switches all amplifiers to mute mode at
low supply voltage and suppresses noise during engine
start
•
No plops when switching between standby and mute
modes
•
Slow offset change when switching from mute mode to
operating mode (can be adjusted by an external
capacitor)
•
A fast mute function by discharging the external mute
capacitor quickly
The following protection circuits are included to prevent
the IC from being damaged:
•
Thermal shutdown:
At junction temperature T
vj
> 170
°
C, all power stages
are switched off to prevent a further increase in
temperature
•
Soft thermal clipping:
At junction temperature T
vj
> 155
°
C, the gain reduces
as temperature increases, resulting in less output power
and decreasing temperature and therefore no thermal
shutdown (no break in the audio)
•
Short-circuit protection:
If a short-circuit to ground or supply voltage occurs at
one or more of the output pins, or across the load of one
or more of the channels, the following action occurs to
reduce power dissipation and case temperature
(see Figs 5 and 6):
– All amplifiers switch off for approximately 20 ms
– After 20 ms the amplifiers switch on again
– If the short-circuit persists, the amplifiers switch off for
another 20 ms period and the action repeats
•
ESD protection:
– Human body model 2000 V
– Machine model 200 V
•
Protection against open ground pins and outputs
short-circuited to supply ground (see Fig.30)
•
All outputs protected are against open power supply
pins and outputs short-circuited to power supply voltage
(see Fig.31)
•
With a reversed polarity power supply an external diode
conducts and a fuse blows and therefore the reversed
polarity voltage will not damage the device (see Fig.32).
7.1
Diagnostic facility
A diagnostic facility is available from the status of pin DIAG
for the following conditions:
•
In normal operation, the level on the DIAG pin is
continuously HIGH (see Fig.3)
•
When a temperature pre-warning occurs due to the
junction temperature T
vj
reaching 145
°
C, the DIAG pin
goes continuously LOW
•
When there is distortion over 2.5% because of clipping,
the DIAG pin has a pulsed output as shown in Fig.4
•
When a short-circuit is detected, the short-circuit
protection becomes active and DIAG goes continuously
LOW for the period of the short-circuit (see Figs 5 and 6)
•
With an extreme output offset, input leakage current
causes a DC output offset voltage and results in power
dissipation in the loudspeakers. Therefore, if the
DC output offset voltage of a bridge is larger than 2 V,
DIAG is pulled LOW to indicate an error condition.
The DIAG pin has an open-drain output to allow several
devices to be tied together. An external pull-up resistor is
needed.
