2002 Jan 14
11
Philips Semiconductors
Preliminary specification
4
×
44 W into 4
Ω
or 4
×
75 W into 2
Ω
quad BTL car radio power amplifier
TDA8591J
7.3
Mute timer and single-pin mute control
The transition time from mute mode to operating mode can
be used to hide plops that occur during switching. This
transition time is determined by the value of the external
capacitor at the MUTE/ON input (see Fig.33). To
guarantee the mute suppression, the resistor value may
not be more than 15 k
Ω
. The switching can be controlled
by a transistor switch with an open-drain output or a
voltage output with a minimum high level of 5.5 V.
When controlling with an open-drain output, the high
voltage level also must be at least 5.5 V and should not be
clamped on a lower value by the ESD diode of the
microcontroller. If the minimum high voltage cannot be
guaranteed, an external open-drain transistor or switch to
ground can be used. Charging of the external capacitor at
the MUTE/ON input is done by an internal current source.
If muting is performed by the microcontroller, the mute
connection to the microcontroller can be omitted. The
mute on and off transitions during start-up and switch-off
are controlled by an internal push-pull current source and
the external capacitor at pin 8 (MUTE/ON).
Fast mute can be achieved by quickly discharging the
mute capacitor by means of an open-drain transistor
without a series resistor.
7.4
Output power
EIAJ power is a power rating which indicates the maximum
possible output power of a specific application at a nominal
supply voltage. The power losses caused by PCB layout,
copper area, connector block, coil, loudspeaker wires, etc.
depend on the applications.
Therefore, the EIAJ power is defined and measured at the
pins of the IC using the following test conditions:
•
The supply voltage is 14.4 V measured on the pins of
the TDA8591J
•
All channels are loaded with 4
Ω
and are driven
simultaneously
•
The input signal is a continuous (no burst) square wave:
V = 1 V (RMS); f = 1 kHz
•
RMS output power is measured immediately at the start
(cold heatsink) and after 1 minute of operation. The
mean value is the rated EIAJ power.
To have optimum output power performance, the external
heatsink should be chosen carefully. A small heatsink
causes a high junction temperature, resulting in an
increase of the drain-source on-state resistance (R
DSon
) of
the power amplifiers and a decrease of the maximum
output power.
The reason for using a square wave input signal for EIAJ
power measurement is illustrated in Fig.9.
Figure 9a shows a square wave signal with
Assuming this square wave is the output signal of an
amplifier, the EIAJ output power is given by
where:
R
L
= load resistor in
Ω
V
top
= maximum voltage across the load in V
f = frequency of the square wave in Hz
t
r
= rise time of the slope in s.
A sine wave has a lower slew rate than a square wave as
shown in Fig.9b, therefore EIAJ power measurement with
a sine wave will give a lower power value. The maximum
slew rate of a sine wave output signal is given by
where:
A = amplitude of the output sinewave in V
f = frequency of the output sinewave in Hz.
For a non-clipping sinewave output with amplitude
A = 13 V and frequency f = 1 kHz, the slew rate is
A faster slew rate can be obtained by increasing the
amplitude: for an amplitude of 28 V, the slew rate will
increase to 1.8
5
V/s. A supply voltage of V
P
= 14.4 V will
result in a clipped output with a shape similar to a square
wave but with a slower slew rate.
Figure 9c shows the dependency of P
EIAJ
on slew rate.
Using a square wave input signal, the EIAJ output power
is determined by the drop voltage and bandwidth of the
output stage.
slew rate
V
top
t
r
----------
=
P
EIAJ
V
top
2
R
L
-------------
1
8
3
---
V
top
×
f
×
–
slew rate
-------------------------------------------
×
=
δ
U
out
δ
t max
------------------
δ
A
sin
×
2
π
f
t
×
(
)
(
)
δ
t max
------------------------------------------------
2
π
f
A
×
=
=
δ
U
out
δ
t max
------------------
82
3
V/s
=
