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TDA7294
®
100V - 100W DMOS AUDIO AMPLIFIER WITH MUTE/ST-BY
VERY HIGH OPERATING VOLTAGE RANGE
(±40V)
DMOS POWER STAGE
HIGH OUTPUT POWER (UP TO 100W MUSIC POWER)
MUTING/STAND-BY FUNCTIONS
NO SWITCH ON/OFF NOISE
NO BOUCHEROT CELLS
VERY LOW DISTORTION
VERY LOW NOISE
SHORT CIRCUIT PROTECTION
THERMAL SHUTDOWN
DESCRIPTION
The TDA7294 is a monolithic integrated circuit in
Multiwatt15 package, intended for use as audio
class AB amplifier in Hi-Fi field applications
(Home Stereo, self powered loudspeakers, Topclass TV). Thanks to the wide voltage range and
MULTIPOWER BCD TECHNOLOGY
Multiwatt15V
Multiwatt15H
ORDERING NUMBERS:
TDA7294V
TDA7294HS
to the high out current capability it is able to supply the highest power into both 4Ω and 8Ω loads
even in presence of poor supply regulation, with
high Supply Voltage Rejection.
The built in muting function with turn on delay
simplifies the remote operation avoiding switching
on-off noises.
Figure 1: Typical Application and Test Circuit
C7 100nF
+Vs
C6 1000µF
R3 22K
C2
22µF
R2
680Ω
IN-
2
IN+
3
IN+MUTE
4
C1 470nF
+Vs
+PWVs
7
13
-
14
C5
22µF
+
R1 22K
VM
R5 10K
VSTBY
MUTE
10
STBY
9
R4 22K
C3 10µF
C4 10µF
OUT
6
MUTE
THERMAL
SHUTDOWN
STBY
BOOTSTRAP
S/C
PROTECTION
1
8
15
STBY-GND
-Vs
-PWVs
C9 100nF
R6
2.7Ω
C10
100nF
C8 1000µF
D93AU011
-Vs
Note: The Boucherot cell R6, C10, normally not necessary for a stable operation it could
be needed in presence of particular load impedances at VS <±25V.
April 2003
1/17
TDA7294
PIN CONNECTION (Top view)
TAB connected to -VS
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGS
Symbol
Value
Unit
Supply Voltage (No Signal)
±50
V
IO
Ptot
Output Peak Current
Power Dissipation Tcase = 70°C
10
50
A
W
0 to 70
150
°C
°C
Top
Tstg, Tj
2/17
Parameter
VS
Operating Ambient Temperature Range
Storage and Junction Temperature
TDA7294
THERMAL DATA
Symbol
Rth j-case
Description
Thermal Resistance Junction-case
Value
Unit
1.5
°C/W
Max
ELECTRICAL CHARACTERISTICS (Refer to the Test Circuit VS = ±35V, RL = 8Ω, GV = 30dB;
Rg = 50 Ω; Tamb = 25°C, f = 1 kHz; unless otherwise specified.
Symbol
Parameter
VS
Iq
Supply Range
Quiescent Current
Ib
Test Condition
Min.
Typ.
Max.
Unit
±10
20
30
±40
65
V
mA
Input Bias Current
500
nA
VOS
Input Offset Voltage
+10
mV
IOS
Input Offset Current
+100
nA
PO
RMS Continuous Output Power
d
d = 0.5%:
VS = ± 35V, RL = 8Ω
VS = ± 31V, RL = 6Ω
VS = ± 27V, RL = 4Ω
Music Power (RMS)
IEC268.3 RULES - ∆t = 1s (*)
d = 10%
RL = 8Ω ; VS = ±38V
RL = 6Ω ; VS = ±33V
RL = 4Ω ; VS = ±29V (***)
Total Harmonic Distortion (**)
PO = 5W; f = 1kHz
PO = 0.1 to 50W; f = 20Hz to 20kHz
60
60
60
Slew Rate
GV
Open Loop Voltage Gain
GV
Closed Loop Voltage Gain
eN
Total Input Noise
100
100
100
W
W
W
0.1
0.01
7
24
A = curve
f = 20Hz to 20kHz
Frequency Response (-3dB)
PO = 1W
Ri
SVR
Input Resistance
Supply Voltage Rejection
f = 100Hz; Vripple = 0.5Vrms
%
%
0.1
%
%
V/µs
30
40
dB
1
2
5
µV
µV
10
80
fL, fH
TS
W
W
W
0.005
VS = ±27V, RL = 4Ω:
PO = 5W; f = 1kHz
PO = 0.1 to 50W; f = 20Hz to 20kHz
SR
70
70
70
dB
20Hz to 20kHz
100
60
Thermal Shutdown
kΩ
75
dB
145
°C
STAND-BY FUNCTION (Ref: -VS or GND)
VST on
Stand-by on Threshold
VST off
ATTst-by
Stand-by off Threshold
Stand-by Attenuation
1.5
3.5
70
Quiescent Current @ Stand-by
Iq st-by
MUTE FUNCTION (Ref: -VS or GND)
VMon
Mute on Threshold
VMoff
Mute off Threshold
3.5
Mute AttenuatIon
60
ATTmute
V
dB
90
1
V
3
mA
1.5
V
V
80
dB
Note (*):
MUSIC POWER CONCEPT
MUSIC POWER is 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.
Note (**): Tested with optimized Application Board (see fig. 2)
Note (***): Limited by the max. allowable current.
3/17
TDA7294
Figure 2: P.C.B. and components layout of the circuit of figure 1. (1:1 scale)
Note:
The Stand-by and Mute functions can be referred either to GND or -VS.
On the P.C.B. is possible to set both the configuration through the jumper J1.
4/17
TDA7294
APPLICATION SUGGESTIONS (see Test and Application Circuits of the Fig. 1)
The recommended values of the external components are those shown on the application circuit of Figure 1. Different values can be used; the following table can help the designer.
LARGER THAN
SUGGESTED
SMALLER THAN
SUGGESTED
INCREASE INPUT
IMPRDANCE
DECREASE INPUT
IMPEDANCE
COMPONENTS
SUGGESTED VALUE
PURPOSE
R1 (*)
22k
INPUT RESISTANCE
R2
680Ω
R3 (*)
22k
R4
22k
ST-BY TIME
CONSTANT
LARGER ST-BY
ON/OFF TIME
SMALLER ST-BY
ON/OFF TIME;
POP NOISE
R5
10k
MUTE TIME
CONSTANT
LARGER MUTE
ON/OFF TIME
SMALLER MUTE
ON/OFF TIME
C1
0.47µF
INPUT DC
DECOUPLING
HIGHER LOW
FREQUENCY
CUTOFF
C2
22µF
FEEDBACK DC
DECOUPLING
HIGHER LOW
FREQUENCY
CUTOFF
C3
10µF
MUTE TIME
CONSTANT
LARGER MUTE
ON/OFF TIME
SMALLER MUTE
ON/OFF TIME
C4
10µF
ST-BY TIME
CONSTANT
LARGER ST-BY
ON/OFF TIME
SMALLER ST-BY
ON/OFF TIME;
POP NOISE
C5
22µF
BOOTSTRAPPING
SIGNAL
DEGRADATION AT
LOW FREQUENCY
C6, C8
1000µF
SUPPLY VOLTAGE
BYPASS
DANGER OF
OSCILLATION
C7, C9
0.1µF
SUPPLY VOLTAGE
BYPASS
DANGER OF
OSCILLATION
CLOSED LOOP GAIN DECREASE OF GAIN INCREASE OF GAIN
SET TO 30dB (**)
INCREASE OF GAIN DECREASE OF GAIN
(*) R1 = R3 FOR POP OPTIMIZATION
(**) CLOSED LOOP GAIN HAS TO BE ≥ 24dB
5/17
TDA7294
TYPICAL CHARACTERISTICS
(Application Circuit of fig 1 unless otherwise specified)
Figure 3: Output Power vs. Supply Voltage.
Figure 4: Distortion vs. Output Power
Figure 5: Output Power vs. Supply Voltage
Figure 6: Distortion vs. Output Power
Figure 7: Distortion vs. Frequency
Figure 8: Distortion vs. Frequency
6/17
TDA7294
TYPICAL CHARACTERISTICS (continued)
Figure 9: Quiescent Current vs. Supply Voltage
Figure 10: Supply Voltage Rejection vs. Frequency
Figure 11: Mute Attenuation vs. Vpin10
Figure 12: St-by Attenuation vs. Vpin9
Figure 13: Power Dissipation vs. Output Power
Figure 14: Power Dissipation vs. Output Power
7/17
TDA7294
INTRODUCTION
In consumer electronics, an increasing demand
has arisen for very high power monolithic audio
amplifiers able to match, with a low cost the performance obtained from the best discrete designs.
The task of realizing this linear integrated circuit
in conventional bipolar technology is made extremely difficult by the occurence of 2nd breakdown phenomenon. It limits the safe operating
area (SOA) of the power devices, and as a consequence, the maximum attainable output power,
especially in presence of highly reactive loads.
Moreover, full exploitation of the SOA translates
into a substantial increase in circuit and layout
complexity due to the need for sophisticated protection circuits.
To overcome these substantial drawbacks, the
use of power MOS devices, which are immune
from secondary breakdown is highly desirable.
The device described has therefore been developed in a mixed bipolar-MOS high voltage technology called BCD 100.
1) Output Stage
The main design task one is confronted with while
developing an integrated circuit as a power operational amplifier, independently of the technology used, is that of realizing the output stage.
The solution shown as a principle shematic by Fig
15 represents the DMOS unity-gain output buffer
of the TDA7294.
This large-signal, high-power buffer must be capable of handling extremely high current and voltage levels while maintaining acceptably low har-
monic distortion and good behaviour over frequency response; moreover, an accurate control
of quiescent current is required.
A local linearizing feedback, provided by differential amplifier A, is used to fullfil the above requirements, allowing a simple and effective quiescent
current setting.
Proper biasing of the power output transistors
alone is however not enough to guarantee the absence of crossover distortion.
While a linearization of the DC transfer characteristic of the stage is obtained, the dynamic behaviour of the system must be taken into account.
A significant aid in keeping the distortion contributed by the final stage as low as possible is provided by the compensation scheme, which exploits the direct connection of the Miller capacitor
at the amplifier’s output to introduce a local AC
feedback path enclosing the output stage itself.
2) Protections
In designing a power IC, particular attention must
be reserved to the circuits devoted to protection
of the device from short circuit or overload conditions.
Due to the absence of the 2nd breakdown phenomenon, the SOA of the power DMOS transistors is delimited only by a maximum dissipation
curve dependent on the duration of the applied
stimulus.
In order to fully exploit the capabilities of the
power transistors, the protection scheme implemented in this device combines a conventional
SOA protection circuit with a novel local temperature sensing technique which " dynamically" controls the maximum dissipation.
Figure 15: Principle Schematic of a DMOS unity-gain buffer.
8/17
TDA7294
Figure 16: Turn ON/OFF Suggested Sequence
+Vs
(V)
+35
-35
-Vs
VIN
(mV)
VST-BY
PIN #9
(V)
VMUTE
PIN #10
(V)
5V
5V
IP
(mA)
VOUT
(V)
OFF
ST-BY
PLAY
MUTE
ST-BY
OFF
MUTE
D93AU013
In addition to the overload protection described
above, the device features a thermal shutdown
circuit which initially puts the device into a muting
state (@ Tj = 145 oC) and then into stand-by (@
Figure 17: Single Signal ST-BY/MUTE Control
Circuit
MUTE
MUTE/
ST-BY
STBY
20K
10K
30K
1N4148
10µF
10µF
D93AU014
Tj = 150 oC).
Full protection against electrostatic discharges on
every pin is included.
3) Other Features
The device is provided with both stand-by and
mute functions, independently driven by two
CMOS logic compatible input pins.
The circuits dedicated to the switching on and off
of the amplifier have been carefully optimized to
avoid any kind of uncontrolled audible transient at
the output.
The sequence that we recommend during the
ON/OFF transients is shown by Figure 16.
The application of figure 17 shows the possibility
of using only one command for both st-by and
mute functions. On both the pins, the maximum
applicable range corresponds to the operating
supply voltage.
9/17
TDA7294
APPLICATION INFORMATION
HIGH-EFFICIENCY
Constraints of implementing high power solutions
are the power dissipation and the size of the
power supply. These are both due to the low efficiency of conventional AB class amplifier approaches.
Here below (figure 18) is described a circuit proposal for a high efficiency amplifier which can be
adopted for both HI-FI and CAR-RADIO applications.
The TDA7294 is a monolithic MOS power amplifier which can be operated at 80V supply voltage
(100V with no signal applied) while delivering output currents up to ±10 A.
This allows the use of this device as a very high
power amplifier (up to 180W as peak power with
T.H.D.=10 % and Rl = 4 Ohm); the only drawback
is the power dissipation, hardly manageable in
the above power range.
Figure 20 shows the power dissipation versus
output power curve for a class AB amplifier, compared with a high efficiency one.
In order to dimension the heatsink (and the power
supply), a generally used average output power
value is one tenth of the maximum output power
at T.H.D.=10 %.
From fig. 20, where the maximum power is
around 200 W, we get an average of 20 W, in this
condition, for a class AB amplifier the average
power dissipation is equal to 65 W.
The typical junction-to-case thermal resistance of
the TDA7294 is 1 oC/W (max= 1.5 oC/W). To
avoid that, in worst case conditions, the chip temperature exceedes 150 oC, the thermal resistance
of the heatsink must be 0.038 oC/W (@ max ambient temperature of 50 oC).
As the above value is pratically unreachable; a
high efficiency system is needed in those cases
where the continuous RMS output power is higher
than 50-60 W.
The TDA7294 was designed to work also in
higher efficiency way.
For this reason there are four power supply pins:
two intended for the signal part and two for the
power part.
T1 and T2 are two power transistors that only operate when the output power reaches a certain
threshold (e.g. 20 W). If the output power increases, these transistors are switched on during
the portion of the signal where more output voltage swing is needed, thus "bootstrapping" the
power supply pins (#13 and #15).
The current generators formed by T4, T7, zener
Figure 18: High Efficiency Application Circuit
+40V
T1
BDX53A
T3
BC394
R4
270
D1 BYW98100
+20V
T4
BC393
270
L1 1µH
D3 1N4148
C11 330nF
C1
1000µF
C3
100nF
C5
1000µF
C7
100nF
C9
330nF
IN
TDA7294
C13 10µF
C4
100nF
C6
1000µF
C8
100nF
R2
2
C10
330nF
D5
1N4148
R13 20K
R6
20K
C11 22µF
R7
3.3K
L3 5µH
14
10
8
15
OUT
R8
3.3K
C17
1.8nF
1
Z2 3.9V
L2 1µH
D4 1N4148
T7
BC394
270
T2
BDX54A
T6
BC393
R9
270
T8
BC394
R10
270
-40V
D93AU016
10/17
C16
1.8nF
270
6
R15 10K
C14
10µF
R3 680
R16
13K
C15
22µF
R14 30K
D2 BYW98100
-20V
13
9
ST-BY
C2
1000µF
7
2
4
PLAY
GND
T5
BC393
Z1 3.9V
3
R16
13K
R1
2
R5
270
R11
29K
TDA7294
Figure 19: P.C.B. and Components Layout of the Circuit of figure 18 (1:1 scale)
diodes Z1,Z2 and resistors R7,R8 define the minimum drop across the power MOS transistors of
the TDA7294. L1, L2, L3 and the snubbers C9,
R1 and C10, R2 stabilize the loops formed by the
"bootstrap" circuits and the output stage of the
TDA7294.
In figures 21,22 the performances of the system
in terms of distortion and output power at various
frequencies (measured on PCB shown in fig. 19)
are displayed.
The output power that the TDA7294 in highefficiency application is able to supply at
Vs = +40V/+20V/-20V/-40V; f =1 KHz is:
- Pout = 150 W @ T.H.D.=10 % with Rl= 4 Ohm
- Pout = 120 W @ "
= 1% " " "
- Pout = 100 W @ "
=10 % with Rl= 8 Ohm
- Pout = 80 W @ "
= 1% " " "
Results from efficiency measurements (4 and 8
Ohm loads, Vs = ±40V) are shown by figures 23
and 24. We have 3 curves: total power dissipation, power dissipation of the TDA7294 and
power dissipation of the darlingtons.
By considering again a maximum average
output power (music signal) of 20W, in case
of the high efficiency application, the thermal
resistance value needed from the heatsink is
2.2oC/W (Vs =±40 V and Rl= 4 Ohm).
All components (TDA7294 and power transistors
T1 and T2) can be placed on a 1.5oC/W heatsink,
with the power darlingtons electrically insulated
from the heatsink.
Since the total power dissipation is less than that
of a usual class AB amplifier, additional cost savings can be obtained while optimizing the power
supply, even with a high headroom.
11/17
TDA7294
Figure 20: Power Dissipation vs. Output Power
Figure 21: Distortion vs. Output Power
HIGH-EFFICIENCY
Figure 22: Distortion vs. Output Power
Figure 24: Power Dissipation vs. Output Power
12/17
Figure 23: Power Dissipation vs. Output Power
TDA7294
BRIDGE APPLICATION
Another application suggestion is the BRIDGE
configuration, where two TDA7294 are used, as
shown by the schematic diagram of figure 25.
In this application, the value of the load must not
be lower than 8 Ohm for dissipation and current
capability reasons.
A suitable field of application includes HI-FI/TV
subwoofers realizations.
The main advantages offered by this solution are:
- High power performances with limited supply
voltage level.
- Considerably high output power even with high
load values (i.e. 16 Ohm).
The characteristics shown by figures 27 and 28,
measured with loads respectively 8 Ohm and 16
Ohm.
With Rl= 8 Ohm, Vs = ±25V the maximum output
power obtainable is 150 W, while with Rl=16
Ohm, Vs = ±35V the maximum Pout is 170 W.
Figure 25: Bridge Application Circuit
+Vs
0.22µF
2200µF
7
3
Vi
0.56µF
13
6
+
22K
14
22µF
-
22K
2
1
4
ST-BY/MUTE
10
TDA7294
15
9
680
8
20K
22K
22µF
10
10K
30K
9
15
8
TDA7294
22µF
3
0.56µF
-Vs
0.22µF
2200µF
1N4148
+
22K
6
14
2
1
4
7
13
22µF
22K
680
D93AU015A
13/17
TDA7294
Figure 26: Frequency Response of the Bridge
Application
Figure 28: Distortion vs. Output Power
14/17
Figure 27: Distortion vs. Output Power
TDA7294
mm
DIM.
MIN.
TYP.
inch
MAX.
MIN.
TYP.
MAX.
A
5
0.197
B
2.65
0.104
C
1.6
0.063
D
1
0.039
E
0.49
0.55
0.019
0.022
F
0.66
0.75
0.026
0.030
G
1.02
1.27
1.52
0.040
0.050
0.060
G1
17.53
17.78
18.03
0.690
0.700
0.710
H1
19.6
0.772
H2
L
OUTLINE AND
MECHANICAL DATA
20.2
0.795
21.9
22.2
22.5
0.862
0.874
0.886
L1
21.7
22.1
22.5
0.854
0.870
0.886
L2
17.65
18.1
0.695
L3
17.25
17.5
17.75
0.679
0.689
0.699
L4
10.3
10.7
10.9
0.406
0.421
0.429
L7
2.65
2.9
0.104
M
4.25
4.55
4.85
0.167
0.179
0.191
M1
4.63
5.08
5.53
0.182
0.200
0.218
0.713
0.114
S
1.9
2.6
0.075
S1
1.9
2.6
0.075
0.102
0.102
Dia1
3.65
3.85
0.144
0.152
Multiwatt15 V
15/17
TDA7294
mm
DIM.
MIN.
TYP.
inch
MAX.
MIN.
TYP.
MAX.
A
5
0.197
B
2.65
0.104
C
1.6
E
0.49
0.55
0.063
0.019
0.022
F
0.66
0.75
0.026
G
1.14
1.27
1.4
0.045
0.050
0.055
G1
17.57
17.78
17.91
0.692
0.700
0.705
H1
19.6
0.030
0.772
H2
20.2
0.795
L
20.57
0.810
L1
18.03
0.710
L2
2.54
0.100
L3
17.25
17.5
17.75
0.679
0.689
0.699
L4
10.3
10.7
10.9
0.406
0.421
0.429
L5
5.28
0.208
L6
2.38
0.094
L7
2.65
2.9
0.104
0.114
S
1.9
2.6
0.075
0.102
S1
1.9
2.6
0.075
0.102
Dia1
3.65
3.85
0.144
0.152
16/17
OUTLINE AND
MECHANICAL DATA
Multiwatt15 H
TDA7294
Information furnished is believed to be accurate and reliable. However, STMicroelectronics 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 STMicroelectronics. Specification mentioned in this publication are
subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products
are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
The ST logo is a registered trademark of STMicroelectronics
© 2003 STMicroelectronics – Printed in Italy – All Rights Reserved
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17/17
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