TDA7298
28W Hi-Fi AUDIO POWER AMPLIFIER
WITH MUTE / STAND-BY
SUPPLY VOLTAGE RANGE UP TO
22V
SPLIT SUPPLY OPERATION
HIGH OUTPUT POWER
(UP TO 28W MUSIC POWER)
LOW DISTORTION
MUTE/STAND-BY FUNCTION
NO SWITCH ON/OFF NOISE
AC SHORT CIRCUIT PROTECTION
THERMAL SHUTDOWN
ESD PROTECTION
DESCRIPTION
The TDA7298 is a monolithic integrated circuit in
Heptawatt package, intended for use as audio
class AB amplifier in TV or Hi-Fi field application.
Thanks to the wide voltage range and to the high
out current capability it's able to supply the high-
est power into both 4
and 8
loads even in
presence of poor supply regulation.
The built in Muting/Stand-by function simplifies
the remote operations avoiding also switching on-
off noises.
May 1997
Heptawatt
ORDERING NUMBER: TDA7298
TEST AND APPLICATION CIRCUIT
1/11
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
V
S
DC Supply Voltage
22
V
I
O
Output Peak Current (internally limited)
4
A
P
tot
Power Dissipation T
case
= 70
C
30
W
T
op
Operating Temperature Range
0 to +70
C
T
stg
, T
j
Storage and Junction Temperature
-40 to +150
C
PIN CONNECTION (Top view)
BLOCK DIAGRAM
TDA7298
2/11
ELECTRICAL CHARACTERISTICS (Refer to the test circuit, G
V
= 32dB; V
S
+ 18V; f = 1KHz; T
amb
=
25
C, unless otherwise specified.)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
V
S
Supply Range
+6
+22
V
I
q
Total Quiescent Current
V
S
= +22V
20
40
70
mA
I
b
Input Bias Current
+0.5
A
V
OS
Input Offset Voltage
+15
mV
I
OS
Input Offset Current
+200
nA
P
O
Music Output Power
IEC268-3 Rules (*)
V
S
= + 20, R
L
= 8
,
d = 10%, t = 1s
28
W
P
O
Output Power (continuous RMS)
d = 10%
RL = 4
V
S
= +14V
R
L
= 8
20
20
24
24
W
W
d = 1%
R
L
= 4
V
S
= +14V
R
L
= 8
17
17
W
W
d
Total Harmonic Distortion
R
L
= 4
V
S
= +14V
P
O
= 0.1 to 10W;
f = 100Hz to 15KHz
R
L
= 8
P
O
= 0.1 to 10W;
f = 100Hz to 15KHz
0.1
0.1
0.7
0.5
%
%
SR
Slew Rate
3
5
V/
s
G
V
Open Loop Voltage Gain
80
dB
e
N
Total Input Noise
A Curve
f = 20Hz to 20KHz
2
3
10
V
V
R
i
Input Resistance
500
K
SVR
Supply Voltage Rejection
f = 100Hz, V
ripple
= 1V
RMS
40
50
dB
T
S
Thermal Shutdown
145
C
MUTE/STAND-BY FUNCTION (Ref. V
S
)
VT
ST-BY
Stand-by - Threshold
1
1.8
V
VT
PLAY
Play Threshold
2.7
4
V
I
q ST-BY
Quiescent Current @ Stand-by
V
pin 3
= 0.5V
1
3
mA
ATT
ST-BY
Stand-by Attenuation
70
90
dB
I
pin3
Pin 3 Current @ Stand-by
1
+10
A
Note (*):
MUSIC POWER CONCEPT
MUSIC POWER is ( according to the IEC clauses n.268-3 of Jan 83) the maximal power which the amplifier is capable of producing across the
rated load resistance (regardless of non linearity) 1 sec after the application of a sinusoidal input signal of frequency 1KHz.
According to this definition our method of measurement comprises the following steps:
1) Set the voltage supply at the maximum operating value -10%
2) Apply a input signal in the form of a 1KHz tone burst of 1 sec duration; the repetition period of the signal pulses is > 60 sec
3) The output voltage is measured 1 sec from the start of the pulse
4) Increase the input voltage until the output signal show a THD = 10%
5) The music power is then V
2
out
/R1
,
where V
out
is the output voltage measured in the condition of point 4) and R1 is the rated load impedance
The target of this method is to avoid excessive dissipation in the amplifier.
THERMAL DATA
Symbol
Description
Value
Unit
R
th j-case
Thermal Resistance Junction-case
Max
2.5
C/W
TDA7298
3/11
APPLICATIONS SUGGESTIONS (See Test and Application Circuit)
The recommended values of the external components are those shown on the application circuit. Differ-
ent values can be used; the following table can help the designer.
Comp.
Value
Purpose
Larger Than
Smaller Than
R1
22K
(*)
Input Impedance
Increase of Input
Impedance
Decrease of Input
Impedance
R2
560
Closed Loop Gain set to
32dB (**)
Decrease of Gain
Increase of Gain
R3
22K
(*)
Increase of Gain
Decrease of Gain
R4
22K
(*)
Input Impedance @ Mute
R5
22K
Stand-by Time Constant
R6
4.7
Frequency Stability
Danger of oscillations
Danger of oscillations
C1
1
F
Input DC Decoupling
Higher Low-frequency
cut-off
C2
10
F
Feedback DC Decoupling
Higher Low-frequency
cut-off
C3
10
F
Stand-by Time Constant
C4
0.100
F
Frequency Stability
Danger of Oscillations
C5, C6
1000
F
Supply Voltage Bypass
(*) R1 = R3 = R4 for POP optimization
(**) Closed Loop Gain has to be
30dB
Figure 1: Output Power vs. Supply Voltage
Figure 2: Distortion vs. Output Power
TYPICAL CHARACTERISTICS
TDA7298
4/11
Figure 3: Output Power vs. Supply Voltage.
Figure 4: Distortion vs. Output Power.
Figure 5: Distortion vs. Frequency.
Figure 6: Distortion vs. Frequency.
Figure 7: Quiescent Current vs. Supply Voltage
Figure 8: Supply Voltage Rejection vs. Frequency.
TDA7298
5/11
Figure 9: Bandwidth.
Figure 10: Output Attenuation & Quiescent Cur-
rent vs. V
pin3
.
Figure 11: Total Power Dissipation & Efficiency
vs. Output Power.
Figure 12: Total Power Dissipation & Efficiency
vs. Output Power.
TDA7298
6/11
Figure 13: P.C. Board and Components Layout of the Circuit of Fig. 14 (1:1 scale)
Figure 14: Demo Board Schematic.
TDA7298
7/11
MUTE/STAND-BY FUNCTION
The pin 3 (MUTE/STAND-BY) controls the ampli-
fier status by three different thresholds, referred
to -V
S
.
When its voltage is lower than the first threshold
(1V, with a +70mV hysteresis), the amplifier is in
STAND-BY and all the final stage current gener-
ators are off. Only the input MUTE stage is on in
order to prevent pop-on problems.
At V
pin3
=1.8V the final stage current generators
are switched on and the amplifier operates in
MUTE.
For V
pin3
=2.7V the amplifier is definitely on
(PLAY condition)
Figure 15.
TDA7298
8/11
SHORT-CIRCUIT PROTECTION
The TDA7298 has an original circuit which pro-
tects the device during accidental short-circuit be-
tween output and GND / -Vs / +Vs, taking it in
STAND-BY mode, so limiting also dangerous DC
current flowing throught the loudspeaker.
If a short-circuit or an overload dangerous for the
final transistors are detected, the concerned SOA
circuit sends out a signal to the latching circuit
(with a 10
s delay time that prevents fast random
spikes from inadvertently shutting the amplifier
off) which makes Q
1
and Q
2
saturate (see Block
Diagram). Q
1
immediately short-circuits to ground
the A point turning the final stage off while Q
2
short-circuits to ground the external capacitor
driving the pin 3 (Mute/Stand-by) towards zero
potential.
Only when the pin 3 voltage becomes lower than
1V, the latching circuit is allowed to reset itself
and restart the amplifier, provided that the short-
circuit condition has been removed. In fact, a win-
dow comparator is present at the output and it is
aimed at preventing the amplifier from restarting if
the output voltage is lower than 0.35 Total Supply
Voltage or higher than 0.65 Total Supply Voltage.
If the output voltage lies between these two
thresholds, one may reasonably suppose the
short-circuit has been removed and the amplifier
may start operating again.
The PLAY/MUTE/STAND-BY function pin (pin 3)
is both ground- and positive supply-compatible
and can be interfaced by means of the R
5
, C
3
net
either to a TTL or CMOS output (
-Processor) or
to a specific application circuit.
The R
5
, C
3
net is fundamental, because connect-
ing this pin directly to a low output impedance
driver such as TTL gate would prevent the correct
operation during a short-circuit. Actually a final
stage overload turns on the protection latching
circuit that makes Q
2
try to drive the pin 3 voltage
under 0.8 V. Since the maximum current this pin
can stand is 3 mA, one must make sure the fol-
lowing condition is met:
R
5
(
V
A
-
0.7V
)
3mA
that yields: R
5, min
= 1.5 K
with V
A
=5V.
In order to prevent pop-on and -off transients, it is
advisable to calculate the C
3
, R
5
net in such a
way that the STAND-BY/MUTE and MUTE/PLAY
threshold crossing slope (positive at the turn-on
and vice-versa) is less than 100 V/sec.
Figure 16: Thermal Protection Block Diagram
THERMAL PROTECTION
The thermal protection operates on the 125
A
current generator, linearly decreasing its value
from 90
C on. By doing this, the A voltage slowly
decreases thus switching the amplifier first to
MUTE (at 145
C) and then to STAND-BY
(155
C).
Figure 17: Maximum Allowable Power Dissipa-
tion vs. Ambient Temperature.
The maximum allowable power dissipation de-
pends on the size of the external heatsink (ther-
mal resistance case-ambient); figure 17 shows
the dissipable power as a function of ambient
temperature for different thermal resistance.
TDA7298
9/11
HEPTAWATT PACKAGE MECHANICAL DATA
DIM.
mm
inch
MIN.
TYP.
MAX.
MIN.
TYP.
MAX.
A
4.8
0.189
C
1.37
0.054
D
2.4
2.8
0.094
0.110
D1
1.2
1.35
0.047
0.053
E
0.35
0.55
0.014
0.022
F
0.6
0.8
0.024
0.031
F1
0.9
0.035
G
2.41
2.54
2.67
0.095
0.100
0.105
G1
4.91
5.08
5.21
0.193
0.200
0.205
G2
7.49
7.62
7.8
0.295
0.300
0.307
H2
10.4
0.409
H3
10.05
10.4
0.396
0.409
L
16.97
0.668
L1
14.92
0.587
L2
21.54
0.848
L3
22.62
0.891
L5
2.6
3
0.102
0.118
L6
15.1
15.8
0.594
0.622
L7
6
6.6
0.236
0.260
M
2.8
0.110
M1
5.08
0.200
Dia
3.65
3.85
0.144
0.152
TDA7298
10/11
Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility for the
consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No
license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications men-
tioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.
SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without ex-
press written approval of SGS-THOMSON Microelectronics.
1997 SGS-THOMSON Microelectronics - All Rights Reserved
HEPTAWATT
TM
is a Trademark of companies belonging to the SGS-THOMSON Microelectronics Group
SGS-THOMSON Microelectronics GROUP OF COMPANIES
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TDA7298
11/11
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