1998 Feb 23
5
NXP Semiconductors
Product specification
3 W mono BTL audio amplifier with DC
volume control
TDA7056AT
FUNCTIONAL DESCRIPTION
The TDA7056AT is a mono BTL output amplifier with DC
volume control. It is designed for use in TVs and monitors
but is also suitable for battery-fed portable recorders and
radios.
In conventional DC volume circuits the control or input
stage is AC-coupled to the output stage via external
capacitors to keep the offset voltage low. In the
TDA7056AT the DC volume control stage is integrated into
the input stage so that no coupling capacitors are required.
With this configuration, a low offset voltage is still
maintained and the minimum supply voltage remains low.
The BTL principle offers the following advantages:
•
Lower peak value of the supply current
•
The frequency of the ripple on the supply voltage is twice
the signal frequency.
Consequently, a reduced power supply with smaller
capacitors can be used which also results in cost
reductions. For portable applications there is a trend to
decrease the supply voltage, resulting in a reduction of
output power at conventional output stages. Using the BTL
principle increases the output power.
The maximum gain of the amplifier is fixed at 35.5 dB.
The DC volume control stage has a logarithmic control
characteristic.
The total gain can be controlled from +35.5 to
−
44 dB.
If the DC volume control voltage is below 0.3 V, the device
switches to the mute mode.
The amplifier is short-circuit proof to ground, V
P
and
across the load. A thermal protection circuit is also
implemented. If the crystal temperature rises above
+150
°
C the gain will be reduced, thereby reducing the
output power. Special attention is given to switch-on and
switch-off clicks, low HF radiation and a good overall
stability.
Power dissipation
Assume V
P
= 12 V; R
L
= 16
Ω
.
The maximum sine wave dissipation is 1.8 W.
The R
th vj-a
of the package is 60 K/W.
Therefore T
amb(max)
= 150
−
60
×
1.8 = 42
°
C.
LIMITING VALUES
In accordance with the Absolute Maximum Rating System (IEC 134).
THERMAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN.
MAX.
UNIT
V
P
supply voltage
−
18
V
V
5, 7
input voltage pins 5 and 7
−
5
V
I
ORM
repetitive peak output current
−
1.25
A
I
OSM
non-repetitive peak output current
−
1.5
A
P
tot
total power dissipation
T
case
<
60
°
C
−
1.5
W
T
amb
operating ambient temperature
−
40
+85
°
C
T
stg
storage temperature
−
55
+150
°
C
T
vj
virtual junction temperature
−
150
°
C
t
sc
short-circuit time
−
1
h
SYMBOL
PARAMETER
CONDITIONS
VALUE
UNIT
R
th(j-a)
thermal resistance from junction to ambient
in free air
60
K/W
