TDA7294 - Datasheet Catalog

® 

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 MU- 

SIC 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 

VM 

VSTBY 

C2 

22µF 

R2 

680Ω 

C1 470nF 

R1 22K 

R5 10K 

R4 22K 

IN- 2 

IN+ 

IN+MUTE 

MUTE 

STBY 

3 

4 

10 

9 

MUTE 

STBY 

1 

- 

+ 

+Vs 

7 13 

8 

THERMAL 

SHUTDOWN 

S/C 

PROTECTION 

15 

+PWVs 

14 

6 

OUT 

C5 

22µF 

BOOT- 

STRAP 

R6 

2.7Ω 

C10 

100nF 

C3 10µF C4 10µF 

STBY-GND 

-Vs 

-PWVs 

C9 100nF C8 1000µF 

-Vs 

D93AU011 

Note: The Boucherot cell R6, C10, normally not necessary for a stable operation it could 

be needed in presence of particular load impedances at V S


PIN CONNECTION (Top view) 

TAB connected to -V S 

BLOCK DIAGRAM 

ABSOLUTE MAXIMUM RATINGS 

Symbol Parameter Value Unit 

V S Supply Voltage (No Signal) ±50 V 

I O Output Peak Current 10 A 

P tot Power Dissipation T case = 70°C 50 W 

T op Operating Ambient Temperature Range 0 to 70 °C 

T stg , T j Storage and Junction Temperature 150 °C 

2/17


THERMAL DATA 

Symbol Description Value Unit 

R th j-case Thermal Resistance Junction-case Max 1.5 °C/W 

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 Test Condition Min. Typ. Max. Unit 

V S Supply Range ±10 ±40 V 

I q Quiescent Current 20 30 65 mA 

I b Input Bias Current 500 nA 

V OS Input Offset Voltage +10 mV 

I OS Input Offset Current +100 nA 

P O RMS Continuous Output Power d = 0.5%: 

V S = ± 35V, R L = 8Ω 

V S = ± 31V, R L = 6Ω 

V S = ± 27V, R L = 4Ω 

Music Power (RMS) 

IEC268.3 RULES - ∆t = 1s (*) 

d = 10% 

R L = 8Ω ; V S = ±38V 

R L = 6Ω ; V S = ±33V 

R L = 4Ω ; V S = ±29V (***) 

d Total Harmonic Distortion (**) P O = 5W; f = 1kHz 

P O = 0.1 to 50W; f = 20Hz to 20kHz 

V S = ±27V, R L = 4Ω: 

P O = 5W; f = 1kHz 

P O = 0.1 to 50W; f = 20Hz to 20kHz 

0.01 

% 

0.1 % 

SR Slew Rate 7 10 V/µs 

G V Open Loop Voltage Gain 80 dB 

G V Closed Loop Voltage Gain 24 30 40 dB 

e N Total Input Noise A = curve 

f = 20Hz to 20kHz 

60 

60 

60 

70 

70 

70 

100 

100 

100 

0.005 

0.1 

1 

2 5 

f L, f H Frequency Response (-3dB) P O = 1W 20Hz to 20kHz 

R i Input Resistance 100 kΩ 

SVR Supply Voltage Rejection f = 100Hz; V ripple = 0.5Vrms 60 75 dB 

T S Thermal Shutdown 145 °C 

STAND-BY FUNCTION (Ref: -V S or GND) 

V ST on Stand-by on Threshold 1.5 V 

V ST off Stand-by off Threshold 3.5 V 

ATT st-by Stand-by Attenuation 70 90 dB 

I q st-by Quiescent Current @ Stand-by 1 3 mA 

MUTE FUNCTION (Ref: -V S or GND) 

V Mon Mute on Threshold 1.5 V 

V Moff Mute off Threshold 3.5 V 

ATT mute Mute AttenuatIon 60 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. 

W 

W 

W 

W 

W 

W 

% 

% 

µV 

µV 

3/17


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


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. 

COMPONENTS SUGGESTED VALUE PURPOSE 

LARGER THAN 

SUGGESTED 

SMALLER THAN 

SUGGESTED 

R1 (*) 22k INPUT RESISTANCE INCREASE INPUT 

IMPRDANCE 

DECREASE INPUT 

IMPEDANCE 

R2 680Ω CLOSED LOOP GAIN DECREASE OF GAIN INCREASE OF GAIN 

SET TO 30dB (**) 

R3 (*) 22k INCREASE OF GAIN DECREASE OF GAIN 

R4 22k ST-BY TIME 

CONSTANT 

R5 10k MUTE TIME 

CONSTANT 

C1 0.47µF INPUT DC 

DECOUPLING 

C2 22µF FEEDBACK DC 

DECOUPLING 

C3 10µF MUTE TIME 

CONSTANT 

C4 10µF ST-BY TIME 

CONSTANT 

LARGER ST-BY 

ON/OFF TIME 

LARGER MUTE 

ON/OFF TIME 

LARGER MUTE 

ON/OFF TIME 

LARGER ST-BY 

ON/OFF TIME 

SMALLER ST-BY 

ON/OFF TIME; 

POP NOISE 

SMALLER MUTE 

ON/OFF TIME 

HIGHER LOW 

FREQUENCY 

CUTOFF 

HIGHER LOW 

FREQUENCY 

CUTOFF 

SMALLER MUTE 

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 

C7, C9 0.1µF SUPPLY VOLTAGE 

BYPASS 

DANGER OF 

OSCILLATION 

DANGER OF 

OSCILLATION 

(*) R1 = R3 FOR POP OPTIMIZATION 

(**) CLOSED LOOP GAIN HAS TO BE ≥ 24dB 

5/17


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 7: Distortion vs. Frequency 

Figure 8: Distortion vs. Frequency 

6/17


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 


7/17


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. 

Figure 15: Principle Schematic of a DMOS unity-gain buffer. 

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 harmonic 

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. 

8/17


Figure 16: Turn ON/OFF Suggested Sequence 

+Vs 

(V) 

+35 

-35 

-Vs 

VIN 

(mV) 

VST-BY 

PIN #9 

(V) 

5V 

VMUTE 

PIN #10 

(V) 

5V 

IP 

(mA) 

VOUT 

(V) 

OFF 

ST-BY 

PLAY 

ST-BY 

OFF 

MUTE 

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 o C) and then into stand-by (@ 

Figure 17: Single Signal ST-BY/MUTE Control 

Circuit 

MUTE/ 

ST-BY 

10K 

20K 

30K 

1N4148 

MUTE 

10µF 

STBY 

10µF 

D93AU014 

Tj = 150 o C). 

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


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 o C/W (max= 1.5 o C/W). To 

avoid that, in worst case conditions, the chip temperature 

exceedes 150 o C, the thermal resistance 

of the heatsink must be 0.038 o C/W (@ max ambient 

temperature of 50 o C). 

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 

+20V 

D1 BYW98100 

T1 

BDX53A 

270 

T3 

BC394 

R4 

270 

T4 

BC393 

R5 

270 

T5 

BC393 

GND 

C1 

1000µF 

C2 

1000µF 

C3 

100nF 

C4 

100nF 

C5 

1000µF 

C6 

1000µF 

C7 

100nF 

C8 

100nF 

C9 

330nF 

R1 

2 

R2 

2 

C10 

330nF 

PLAY 

ST-BY 

IN 

D5 

1N4148 

C11 330nF 

R16 

13K 

C13 10µF 

R13 20K 

R14 30K 

R15 10K 

C14 

10µF 

3 

4 

9 

10 

7 

13 


8 15 

L1 1µH 

2 

14 

6 

1 

L2 1µH 

R16 

13K 

D3 1N4148 

C11 22µF 

R3 680 

C15 

22µF 

L3 5µH 

270 

D4 1N4148 

Z1 3.9V 

Z2 3.9V 

R7 

3.3K 

R8 

3.3K 

R6 

20K 

C16 

1.8nF 

OUT 

C17 

1.8nF 

-20V 

-40V 

D2 BYW98100 

270 

T2 

BDX54A 

T6 

BC393 

T7 

BC394 

R9 

270 

R10 

270 

D93AU016 

T8 

BC394 

R11 

29K 

10/17


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 

2.2 o C/W (Vs =±40 V and Rl= 4 Ohm). 

All components (TDA7294 and power transistors 

T1 and T2) can be placed on a 1.5 o C/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




HIGH-EFFICIENCY 




12/17


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 

Vi 

0.22µF 

2200µF 

3 

7 

+ 

13 

6 

14 

22µF 

0.56µF 

22K 

1 

- 

2 

22K 

ST-BY/MUTE 

4 


15 8 

680 

20K 

10 9 

+ 

22µF 

1N4148 

22K 

-Vs 

2200µF 0.22µF 

10K 

30K 

22µF 

10 9 15 8 

3 


6 

14 

22µF 

0.56µF 

22K 

1 

- 

2 

22K 

4 

7 

13 

680 

D93AU015A 

13/17


Figure 26: Frequency Response of the Bridge 

Application 



14/17


DIM. 

mm 

inch 

MIN. TYP. 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 20.2 0.795 

L 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 0.713 

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 0.114 

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 

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 

OUTLINE AND 

MECHANICAL DATA 

Multiwatt15 V 

15/17


DIM. 

mm 

inch 

MIN. TYP. MAX. MIN. TYP. MAX. 

A 5 0.197 

B 2.65 0.104 

C 1.6 0.063 

E 0.49 0.55 0.019 0.022 

F 0.66 0.75 0.026 0.030 

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 0.772 

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 

OUTLINE AND 

MECHANICAL DATA 

Multiwatt15 H 

16/17


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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. 

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17/17

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