TDA7374B
DUAL BRIDGE AUDIO AMPLIFIER FOR CAR RADIO
MINIMUMEXTERNAL COMPONENTCOUNT
NO BOOTSTRAPCAPACITORS
NO BOUCHEROTCELLS
CLIP DETECTOR OUTPUT
HIGHOUTPUT POWER
FIXED GAIN
VERYLOW STAND-BYCURRENT (1µA typ)
NO SWITCH ON/OFF NOISE
PROTECTIONS:
OUTPUT AC/DC SHORT CIRCUIT TO GND
ANDTO V
S
VERYINDUCTIVE LOADS
OVERRATINGCHIP TEMPERATURE
LOADDUMP VOLTAGE
FORTUITOUS OPEN GND
REVERSEBATTERY
ESD
DESCRIPTION
The TDA7374B is a new technology class AB
Audio Dual Bridge Power Amplifier in Multiwatt
packagedesignedfor car radio applications.
Thanks to the fully complementaryPNP/NPN output configuration the high power performances of
the TDA7374B are obtained without bootstrap capacitors.
April 1995
TEST AND APPLICATION CIRCUIT
MULTIWATT15
ORDERING NUMBERS: TDA7374BV
1/13
PIN CONNECTION (Top view)
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
V
S
DC Supply Voltage 28 V
V
OP
Operating Supply Voltage 18 V
V
PEAK
Peak Supply Voltage (t = 50ms) 50 V
I
O
Output Peak Current (not rep. t = 100µs) 4.5 A
I
O
Output Peak Current (rep. f > 10Hz) 3.5 A
P
tot
Power Dissipation (T
case
=85°C) 36 W
T
stg,Tj
Storage and Junction Temperature -40 to 150 °C
THERMAL DATA
Symbol Description Value Unit
R
th j-case
Thermal Resistance Junction-case Max 1.8 °C/W
TDA7374B
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ELECTRICAL CHARACTERISTICS (Referto the test circuit;VS=14.4V; RL=4Ω,T
amb
=25°C,
f = 1kHz, unlessotherwise specified)
Symbol Parameter Test Condition Min. Typ. Max. Unit
V
S
Supply Range 8 18 V
I
d
Total Quiescent Drain Current RL= ∞ 150 mA
P
O
Output Power RL=4Ω; THD = 10% 17 21 W
d Distortion R
L
=4ΩPO= 0.1 to 10W 0.5 %
CT Cross-Talk f = 1kHz
f = 10kHz
65
55
dB
dB
R
IN
Input Impedance 10 KΩ
G
V
Voltage Gain 26 dB
G
V
Voltage Gain Match. 1 dB
E
IN
Input Noise Voltage Rg= 0 to 10kΩ Weight A
22Hz to 22KHz
3.5
10
µV
µV
SVR Supply Voltage Rejection R
g
= 0; f = 100Hz
f = 10kHz
48
55
dB
ASB Stand-by Attenuation 60 dB
I
SB
ST-BY Current 1 µA
V
SB ON
ST-BY On Threshold Voltage 1.5 V
V
SB OFF
ST-BY Off Threshold Voltage 3.5 V
V
OS
Output Offset Voltage 200 mV
I
CD OFF
ClippingDetector ”OFF”
Output Average Current
THD = 1% (*) 100 µA
I
CD ON
ClippingDetector ”ON ”
Output Average Current
THD = 10% (*) 190 µA
(*) Pin 10 Pulled-up to 5V with 10kΩ;RL=4Ω
TDA7374B
3/13
TEST AND APPLICATION CIRCUIT
P.C. BOARDAND COMPONENTLAYOUT (1:1 scale)
B
TDA7374B
4/13
Figure1: QuiescentDrainCurrent vs. Supply
Voltage
Figure2: QuiescentOutputVoltagevs. Supply
Voltage
Figure3: Output Power vs. Supply Voltage
Figure5: Output Power vs. Frequency
Figure4: Distortionvs. OutputPower
Figure6: SupplyVoltageRejectionvs.
Frequencyfor a Different values of C6
Capacitor
R
g
TDA7374B
5/13
Figure7: Cross-Talkvs. Frequency
Figure9: Stand-by Attenuationvs. Threshold
Voltage
Figure8: En Input vs. Rg
Figure11: Clipping Detector Average Current
(Pin 10) vs. Distortion
Figure12: TotalPower Dissipationand
Efficiencyvs.Output Power
Figure10: Stand-byAttenuationvs.Input Voltage
R
g
R
g
TDA7374B
6/13
OUTPUTSTAGE
The fully complementary output stage was made
possible by the development of a new component: the ST exclusive power ICV PNP.
A novel design based upon the connection shown
in fig. 13 has then allowed the full exploitation of
its possibilities.
The clear advantagesthisnew approachhas over
classicaloutput stages are as follows:
1 - Rail-to-Rail Output Voltage Swing With No
NeedOf BootstrapCapacitors.
The output swing is limited only by the Vcesat of
the output transistors, which are in the range of
0.6 Ohm each.
Classical solutions adoptingcomposite PNP-NPN
for the upper output stage have higher saturation
loss on the top side of the waveform. This unbalanced saturation causes a significant power reduction. The only way to recover power consists
of the addition of expensivebootstrap capacitors.
2 - Absolute Stability Without Any External
Compensation.
Referring to the circuit of Fig. 13 the gain
V
OUT/VIN
is greater than unity, approximately 1 +
R2/R1.The DC Output (V
CC
/2) is fixedby an aux-
iliaryamplifiercommon to all the channels).
By controlling the amount of this local feedback it
is possible to force the loop gain (A * β) to less
than unity at frequency for which the phase shift
is 180 Deg. This means that the output buffer is
intrinsicallystable and not prone to oscillation.
Most remarkably, the above feature has been
achievedin spite of the very low closed loop gain
of the amplifier.
In contrast, with the classical PNP-NPN stage,
the solution adopted for reducing the gain at high
frequencies makes use of external RC networks,
namelythe Boucherot cells.
OTHEROUTSTANDINGCHARACTERISTICS:
Clipping Detector Output
The TDA7374B is equipped with an internal circuitable to detect the outputstage saturationproviding a proper current sinking into a open collector output (pin 10) when a certain distortion level
isreached at each output.
This particular function allows gain compression
facility whenever the amplifier is overdriven, thus
obtaininghigh quality sound at all listeninglevels.
Figure13: The new OutputStage
Figure14: Clipping DetectionWaveforms
TDA7374B
7/13
OffsetControl
The quiescent output voltage must be as close as
possible to its nominal value, so that less undistortedpower wouldbe available.
For this reason an input bias current compensation is implemented to riduce the voltage drop
across the input resistors, which appears amplified at the outputs.
Gain Internally Fixed to 26dB
Advantagesof thisdesign choiceare in termsof:
componentsand spacesaving
output noise, supply voltage rejection and dis-
tortionoptimization.
Silent Turn On/Off and Muting/Stand-by Function
The stand-bycan be easily activated by means of
a CMOS level applied to pin 7 througha RC filter.
Under stand-by condition the device is turned off
completely(supply current= 1 µA TYP ; output attenuation=90 dB TYP).
Every ON/OFF operation is virtuallypop free.
Furthermore,at turn-on the devicestaysin muting
condition for a time determined by the value assigned to the SVR capacitor (T= Csvr * 7,000).
While in muting the device outputs becomes insensitive to any kinds of signal that may be present at the input terminals. In other words every
transient coming from previous stages produces
no unpleasantacoustic effect to the speakers.
Anothersituation under which the device is totally
muted is whenever the supply voltage drops
lower than 7V. This is helpful to pop suppression
duringthe turn-off by battery switch.
BUILT-INPROTECTION SYSTEMS
Full Protection of Device and Loudspeakers
Against AC/DC Short Circuits (to Gnd, to Vs,
acrossthe Speakers).
Reliable and safe operation in presence of all
kinds of short circuit involving the outputs is assuredby a built-in protectionsystem that operates
in the following way:
In case of overload, a SCR is activated as soon
as the current flowing through the output transistors overcomes a preset threshold value depending on the chip temperature. The SCR causes an
interruption of the supply current of the power
transistor.
Load Dump Voltage Surge
The TDA 7374 has a circuit which enables it to
withstand a voltage pulse train on pins 3 and 13,
of the type shownin fig. 16.
If the supply voltage peaks to more than 50V,
then an LC filter must be inserted between the
supply and pins 3 and 13, in order to assure that
the pulses at pins 3 and 13 will be held within the
limitsshown.
A suggestedLC network isshown in fig. 15.
With this network, a trainof pulses with amplitude
up to 120V and width of 2ms can be applied at
point A. This type of protection is ON when the
supply voltage (pulse or DC) exceeds 18V. For
this reason the maximum operating supply voltage is 18V.
PolarityInversion
High current (up to 10A) can be handled by the
device with no damage for a longer period than
the blow-out time of a quick 2A fuse (normally
connected in series with the supply). This featuresis added to avoid destruction,if during fitting
to the car, a mistake on the connection of the
supplyis made.
OpenGround
When the radio is in the ON condition and the
ground is accidentally opened, a standard audio
amplifierwill be damaged. On the TDA7374Bprotectiondiodes are includedto avoidany damage.
InductiveLoad
A protection diode is provided to allow use of the
TDA7374Bwithinductiveloads.
Figure15
Figure16
TDA7374B
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DC Voltage
The maximum operating DC voltage for the
TDA7374Bis 18V.
However the device can withstand a DC voltage
up to 28V with no damage. This could occur during winter if two batteries are series connectedto
crankthe engine.
ThermalShut-down
The presence of a thermal limiting circuit offers
the following advantages:
1)an overloadon the output (even if it is permanent), or an excessive ambient temperature
can be easily withstood.
2)the heatsink can have a smaller factor of
safety compared with that of a conventional
circuit. There is no device damage in case of
excessive junction temperature: all happens
is that P
o
(and therefore P
tot
) and Idare re-
duced.
The maximum allowable power dissipation depends upon the size of the external heatsink (i.e.
its thermal resistance); Fig. 17 shows the dissipable power as a function of ambienttemperature
for different thermal resistance.
Loudspeaker Protection
The TDA7374B guarantees safe operations even
for the loudspeaker in case of accidental shortcircuit.
Whenevera single OUT to GND, OUT to V
S
short
circuit occurs both the outputs are switched OFF
so limiting dangerous DC current flowing through
the loudspeaker.
Figure17: MaximumAllowablePower
Dissipationvs. AmbientTemperature
TDA7374B
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CLIPPINGDETECTOR
Fig 19 shows an application using the TDA7374B
in combination with the SGS-THOMSON audioprocessorTDA7302.
Theoutputclippingis recognizedby the microprocessor(in this applicationit is simulatedbya PC).
The detailed way to operate of the system is representedby the flow-chart of fig.18.
The controller detects when the clipping is active
(minimun detection width fixed by a C29 = 12 nF
external capacitor), and reduces the volume (or
bass) bystep of 2 dB (with a programmablewaiting time), until no more clipping is detected.
Then the controllerwaits for a programmabletime
before increasing the volume again by step of 2
dBuntil clippingis again detected or the panel selectedvolume is reached.
Practicaladvantages of this application is a better
sound quality deriving from operation under no
clipping conditions, which also means the availability of higherundistortedpower.
WHAT IS NEEDED FOR A DEMONSTRATION
- a XT or AT IBM compatible PC, supplied with
EGA card
- a SGS-THOMSON audioprocessorapplicationdisk
- a TDA7302 + TDA7374Bboard
- a connector from audioprocessor board to PC
parallelport
GENERALINFORMATION
In the application shown in fig 18 the TDA7302
audioprocessorworks on PC XT or AT IBM compatible.
Control is accomplished by serial bus ( S-bus or
I
2
C-bus or SPIbus) sent to the test board through
the PC parallel port.
ThePC simulates the behaviour of the microproc-
essor in a real application (for example in a car
radio) and the buffer is necessary only in this applicationfor protectingthe PC.
Figure:18: ClippingDetectorControl Routine
TDA7374B
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Figure19: Applicationwith TDA7302+ TDA7374B
TDA7374B
TDA7374B
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MULTIWATT15 (Vertical) PACKAGE MECHANICAL DATA
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
TDA7374B
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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 ofpatents or otherrights of third parties which may result from itsuse. No
license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications mentioned 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 express written approval of SGS-THOMSON Microelectronics.
1995 SGS-THOMSON Microelectronics - All RightsReserved
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TDA7374B
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