TDA7350A
22W BRIDGE-STEREO AMPLIFIER FOR CAR RADIO
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General Features
Figure 1. Package
VERY FEW EXTERNAL COMPONENTS
NO BOUCHEROT CELLS
NO BOOSTRAP CAPACITORS
HIGH OUTPUT POWER
NO SWITCH ON/OFF NOISE
VERY LOW STAND-BY CURRENT
FIXED GAIN (30dB STEREO)
PROGRAMMABLE TURN-ON DELAY
1.1 PROTECTIONS
■ OUTPUT AC-DC SHORT CIRCUIT TO
GROUND AND TO SUPPLY VOLTAGE
■ VERY INDUCTIVE LOADS
■ LOUDSPEAKER PROTECTION
■ OVERRATING CHIP TEMPERATURE
■ LOAD DUMP VOLTAGE
■ FORTUITOUS OPEN GROUND
■ ESD
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Description
Multiwatt11
Table 1. Order Codes
TDA7350A
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Part Number
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Package
Multiwatt11
dio Power Amplifier in the Multiwatt® package designed for car radio applications.
The TDA7350A is a new technology class AB Au-
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Thanks to the fully complementary PNP/NPN output configuration the high power performance of
the TDA7350A is obtained without bootstrap capacitors.
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A delayed turn-on mute circuit eliminates audible
on/off noise, and a novel short circuit protection
system prevents spurious intervention with highly
inductive loads.
Figure 2. Application Circuit (Bridge)
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February 2005
Rev. 1
1/23
TDA7350A
Figure 3. Pin connection (Top view)
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Table 2. Absolute Maximum Ratings
Symbol
bs
Parameter
VS
Operating Supply Voltage
VS
DC Supply Voltage
VS
Peak Supply Voltage (t = 50ms)
IO
Output Peak Current (non rep. t = 100µs)
IO
Output Peak Current (rep. freq. > 10Hz)
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Ptot
Power Dissipation at Tcase = 85°C
Tstg, Tj
Storage and Junction Temperature
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Table 3. Thermal Data
Symbol
Rthj-case
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Parameter
Thermal Resistance Junction-case
Max.
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Value
Unit
18
V
28
V
40
V
5
A
4
A
36
W
-40 to 150
°C
Value
Unit
1.8
°C/W
Table 4. Electrical Characteristcs
(Refer to the test circuits, Tamb = 25°C, VS = 14.4V, f = 1KHz unless otherwise specified)
Symbol
VS
Id
Parameter
Stand-by attenuation
ISB
Stand-by Current
Tsd
Thermal Shut-down
Temperature
Min.
Typ.
8
Total Quiescent Drain Current
ASB
2/23
Test Condition
Supply Voltage Range
stereo configuration
60
Max.
Unit
18
V
120
mA
80
dB
100
Junction
150
µA
°C
TDA7350A
Table 4. Electrical Characteristcs (continued)
(Refer to the test circuits, Tamb = 25°C, VS = 14.4V, f = 1KHz unless otherwise specified)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
7
11
8
6.5
W
W
W
9
6.5
5.5
W
W
W
STEREO
Po
Output Power (each channel)
d = 10%
RL= 2Ω
RL= 3.2Ω
RL= 4Ω
d = 10%; VS= 13.2V
RL= 2Ω
RL= 3.2Ω
RL= 4Ω
d
SVR
CT
Distortion
Po = 0.1 to 4W; RL = 3.2Ω
Supply Voltage Rejection
Rg = 10kΩ f = 100Hz
C3 = 22µF
C3 = 100µF
Crosstalk
RI
Input Resistance
GV
Voltage Gain
GV
Voltage Gain Match
EIN
Input Noise Voltage
45
30
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BRIDGE
Po
45
f = 1KHz
f = 10KHz
Rg= 50Ω(*)
Rg= 10KΩ(*)
Rg = 50Ω(**)
Rg= 10KΩ(**)
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Output Power
d = 10%; RL= 4Ω
d = 10%; RL= 3.2Ω
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Distortion
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VOS
Output Offset Voltage
SVR
Supply Voltage Rejection
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RI
Input Resistance
GV
Voltage Gain
EIN
Input Noise Voltage
d = 10%; VS = 13.2V
RL= 4Ω
RL= 3.2Ω
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50
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50
50
29
1.5
2
2
2.7
dB
dB
dB
dB
KΩ
31
dB
1
dB
7
µV
µV
µV
µV
W
W
17.5
19
W
W
45
50
57
33
35
1
%
250
mV
dB
dB
50
Rg= 50Ω(*)
Rg= 10KΩ(*)
Rg = 50Ω(**)
Rg= 10KΩ(**)
%
20
22
Po= 0.1 to 10W; RL = 4W
Rg = 10kΩ f = 100Hz
C3 = 22µF
C3 = 100µF
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0.5
2
2.5
2.7
3.2
KΩ
37
dB
µV
µV
µV
µV
(*) Curve A
(**) 22Hz to 22KHz
3/23
TDA7350A
Figure 4. STEREO Test and Appication Circuit
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Figure 5. P.C. Board and Layout (STEREO) of the circuit of fig. 4
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TDA7350A
Figure 6. BRIDGE Test and Appication Circuit
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Figure 7. P.C. Board and Layout (BRIDGE) of the circuit of fig. 6
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TDA7350A
Table 5. Recommended Values of the External Components
(ref. to the Stereo Test and Application Circuit)
Component
Recommended
Value
C1
0.22µF
C2
Larger than the Recomm.
Value
Smaller than the Recomm.
Value
Input
Decoupling (CH1)
—
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0.22µF
Input Decoupling
(CH2)
—
—
C3
100µF
Supply Voltage
Rejection
Filtering
Capacitor
Longer Turn-On Delay
Time
C4
22µF
Stand-By
ON/OFF Delay
Delayed Turn-Off by Stand- Danger of Noise (POP)
By Switch
C5
220µF (min)
Supply By-Pass
C6
100nF (min)
Supply By-Pass
C7
2200µF
Purpose
Worse Supply Voltage
Rejection.
Shorter Turn-On Delay Time
Danger of Noise (POP)
Danger of Oscillations
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Danger of Oscillations
- Decrease of Low Frequency
Cut Off
- Longer Turn On Delay
Output
Decoupling
CH2
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- Increase of Low Frequency
Cut Off
- Shorter Turn On Delay
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Figure 8. Output Power vs. Supply Voltage
(Stereo)
Figure 10. Output Power vs. Supply Voltage
(Stereo)
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Figure 9. Output Power vs. Supply Voltage
(Stereo)
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Figure 11. Output Power vs. Supply Voltage
(Bridge)
TDA7350A
Figure 12. Output Power vs. Supply Voltage
(Bridge)
Figure 15. Distortion vs Output Power
(Stereo)
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Figure 16. Distortion vs Output Power
(Stereo)
Figure 13. Drain Current vs Supply Voltage
(Stereo)
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Figure 14. Distortion vs Output Power
(Stereo)
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Figure 17. Distortion vs Output Power
(Bridge)
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TDA7350A
Figure 21. SVR vs. Frequency & CSVR;
(Bridge)
Figure 18. SVR vs. Frequency & CSVR
(Stereo)
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Figure 22. Crosstalk vs. Frequency
(Stereo)
Figure 19. SVR vs. Frequency & CSVR;
(Stereo)
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Figure 20. SVR vs. Frequency & CSVR;
(Bridge)
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Figure 23. Power Dissipation & Efficiency vs.
Output Power (Stereo)
TDA7350A
Figure 24. Power Dissipation & Efficiency vs.
Output Power (Stereo)
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The TDA7350A has been developed taking care of
the key concepts of the modern power audio amplifier for car radio such as: space and costs saving due to the minimized external count, excellent
electrical performances, flexibility in use, superior
reliability thanks to a built-in array of protections.
As a result the following performances has been
achieved:
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Figure 25. Power Dissipation & Efficiency vs.
Output Power (Bridge)
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Figure 26. Power Dissipation & Efficiency vs.
Output Power (Bridge))
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NO NEED OF BOOTSTRAP CAPACITORS
EVEN AT THE HIGHEST OUTPUT POWER
LEVELS
ABSOLUTE STABILITY WITHOUT EXTERNAL
COMPENSATION THANKS TO THE NNOVATIVE OUT STAGE CONFIGURATION, ALSO
ALLOWING INTERNALLY FIXED LOSED
LOOP LOWER THAN COMPETITORS
LOW GAIN (30dB STEREO FIXED WITHOUT
ANY EXTERNAL COMPONENTS) IN ORDER
TO MINIMIZE THE OUTPUT NOISE AND OPTIMIZE SVR
SILENT MUTE/ST-BY FUNCTION FEATURING ABSENCE OF POP ON/OFF NOISE
HIGH SVR
STEREO/BRIDGE OPERATION WITHOUT
ADDITION OF EXTERNAL COMPONENT
AC/DC SHORT CIRCUIT PROTECTION (TO
GND, TO VS, ACROSS THE LOAD)
LOUDSPEAKER PROTECTION
DUMP PROTECTION
ESD PROTECTION
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Amplifier Organization
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Block Description
4.1 Polarization
The device is organized with the gain resistors directly connected to the signal ground pin i.e. without gain capacitors (fig. 27).
The non inverting inputs of the amplifiers are connected to the SVR pin by means of resistor dividers, equal to the feedback networks. This allows
the outputs to track the SVR pin which is sufficiently slow to avoid audible turn-on and turn-off transients.
4.2 SVR
The voltage ripple on the outputs is equal to the
one on SVR pin: with appropriate selection of CSVR, more than 55dB of ripple rejection can be obtained.
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TDA7350A
4.3 Delayed Turn-on (muting)
The CSVR sets a signal turn-on delay too. A circuit is included which mutes the device until the voltage
on SVR pin reaches ~2.5V typ (fig. 28). The mute function is obtained by duplicating the input differential
pair (fig. 29): it can be switched to the signal source or to an internal mute input. This feature is necessary
to prevent transients at the inputs reaching the loudspeaker(s) immediately after power-on).
Fig. 28 represents the detailed turn-on transient with reference to the stereo configuration. At the poweron the output decoupling capacitors are charged through an internal path but the device itself remains
switched off (Phase 1 of the represented diagram).
When the outputs reach the voltage level of about 1V (this means that there is no presence of short circuits) the device switches on, the SVR capacitor starts charging itself and the output tracks exactly the
SVR pin.
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During this phase the device is muted until the SVR reaches the "Play" threshold (~2.5V typ.), after that
the music signal starts being played.
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4.4 Stereo/Bridge Switching
There is also no need for external components for changing from stereo to bridge configuration (figg. 2730). A simple short circuit between two pins allows phase reversal at one output, yet maintaining the quiescent output voltage.
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4.5 Stand-by
The device is also equipped with a stand-by function, so that a low current, and hence low cost switch,
can be used for turn on/off.
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4.6 Stability
The device is provided with an internal compensation wich allows to reach low values of closed loop gain.
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In this way better performances on S/N ratio and SVR can be obtained.
Figure 27. Block Diagram; Stereo Configuration
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Figure 28. Turn-on Delay Circuit
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Figure 29. Mute Function Diagram
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TDA7350A
Figure 30. Block Diagram; Bridge Configuration
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Figure 31. ICV - PNP Gain vs. IC
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Figure 33. ICV - PNP cut-off frequency vs. IC
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Figure 32. ICV - PNP VCE(sat) vs. IC
4.7 OUTPUT STAGE
Poor current capability and low cutoff frequency
are well known limits of the standard lateral PNP.
Composite PNP-NPN power output stages have
been widely used, regardless their high saturation
drop. This drop can be overcome only at the expense of external components, namely, the bootstrap capacitors. The availability of 4A isolated
collector PNP (ICV PNP) adds versatility to the design. The performance of this component, in terms
of gain, VCEsat and cut-off frequency, is shown in
fig. 31, 32, 33 respectively. It is realized in a new
bipolar technology, characterized by topbottom
isolation techniques, allowing the implementation
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TDA7350A
of low leakage diodes, too. It guarantees BVCEO > 20V and BVCBO > 50V both for NPN and PNP transistors. Basically, the connection shown in fig. 34 has been chosen. First of all because its voltage swing is
rail-to-rail, limited only by the VCEsat of the output transistors, which are in the range of 0.3Ω each. Then,
the gain VOUT/VIN is greater than unity, approximately 1+R2/R1. (VCC/2 is fixed by an auxiliary amplifier
common to both channel). It is possible, controlling the amount of this local feedback, to force the loop
gain (A . β) to less than unity at frequencies for which the phase shift is 180°. This means that the output
buffer is intrinsically stable and not prone to oscillation.
Figure 34. The New Output Stage
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In contrast, with the circuit of fig. 35, the solution adopted to reduce the gain at high frequencies is the use
of an external RC network.
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4.8 AMPLIFIER BLOCK DIAGRAM
The block diagram of each voltage amplifier is shown in fig. 36. Regardless of production spread, the current in each final stage is kept low, with enough margin on the minimum, below which cross-over distortion
would appear.
Figure 35. A Classical Output Stage
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Figure 36. Amplifier Block Diagram
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TDA7350A
4.9 BUILT-IN PROTECTION SYSTEMS
4.9.1 Short Circuit Protection
The maximum current the device can deliver can be calculated by considering the voltage that may be
present at the terminals of a car radio amplifier and the minimum load impedance.
Apart from consideration concerning the area of the power transistors it is not difficult to achieve peak currents of this magnitude (5A peak).
However, it becomes more complicated if AC and DC short circuit protection is also required.In particular,
with a protection circuit which limits the output current following the SOA curve of the output transistors it
is possible that in some conditions (highly reactive loads, for example) the protection circuit may intervene
during normal operation. For this reason each amplifier has been equipped with a protection circuit that
intervenes when the output current exceeds 4A.
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Fig 37 shows the protection circuit for an NPN power transistor (a symmetrical circuit applies to PNP).The
VBE of the power is monitored and gives out a signal,available through a cascode.
This cascode is used to avoid the intervention of the short circuit protection when the saturation is below
a given limit.
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The signal sets a flip-flop which forces the amplifier outputs into a high impedance state.
In case of DC short circuit when the short circuit is removed the flip-flop is reset and restarts the circuit
(fig. 41). In case of AC short circuit or load shorted in Bridge configuration, the device is continuously
switched in ON/OFF conditions and the current is limited.
Figure 37. Circuitry for Short Circuit Detection
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4.9.2 Load Dump Voltage Surge
The TDA7350A has a circuit which enables it to withstand a voltage pulse train on pin 9, of the type shown
in fig. 39.
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If the supply voltage peaks to more than 40V, then an LC filter must be inserted between the supply and
pin 9, in order to assure that the pulses at pin 9 will be held within the limits shown.
A suggested LC network is shown in fig. 38. With this network, a train of 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.
Figure 38.
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TDA7350A
Figure 39.
4.9.3 Polarity Inversion
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 features is
added to avoid destruction, if during fitting to the
car, a mistake on the connection of the supply is
made.
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pable power as a function of ambient temperature
for different thermal resistance.
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Figure 40. Maximum Allowable Power
Dissipation vs. Ambient Temperature
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4.10 Open Ground
When the radio is in the ON condition and the
ground is accidentally opened, a standard audio
amplifier will be damaged. On the TDA7350A protection diodes are included to avoid any damage.
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4.10.1DC Voltage
The maximum operating DC voltage for the
TDA7350A is 18V. However the device can withstand a DC voltage up to 28V with no damage.
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This could occur during winter if two batteries are
series connected to crank the engine.
The TDA7350A guarantees safe operations even
for the loudspeaker in case of accidental shortcircuit.
4.10.2Thermal Shut-down
The presence of a thermal limiting circuit offers the
following advantages:
1) an overload on 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 the case of excessive junction temperature: all happens is that Po
(and therefore Ptot) and Id are reduced.
The maximum allowable power dissipation depends upon the size of the external heatsink (i.e.
its thermal resistance); Fig. 40 shows the dissi-
Whenever a single OUT to GND, OUT to VS short
circuit occurs both the outputs are switched OFF
so limiting dangerous DC current flowing through
the loudspeaker.
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Figure 41. Restart Circuit
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TDA7350A
5
Application Hints
Figure 42.
This section explains briefly how to get the best
from the TDA7350A and presents some application circuits with suggestions for the value of the
components.These values can change depending
on the characteristics that the designer of the car
radio wants to obtain,or other parts of the car radio
that are connected to the audio block.
a) Csvr = 22 µF
To optimize the performance of the audio part it is
useful (or indispensable) to analyze also the parts
outside this block that can have an interconnection
with the amplifier.
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This method can provide components and system
cost saving.
5.1 Reducing Turn On-Off Pop
The TDA7350A has been designed in a way that
the turn on(off) transients are controlled through
the charge(discharge) of the Csvr capacitor.
As a result of it, the turn on(off) transient spectrum
contents is limited only to the subsonic range.The
following section gives some brief notes to get the
best from this design feature(it will refer mainly to
the stereo application which appears to be in most
cases the more critical from the pop viewpoint.The
bridge connection in fact,due to the common mode
waveform at the outputs,does not give pop effect).
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5.2 TURN-ON
Fig. 42 shows the output waveform (before and after the "A" weighting filter) compared to the value
of Csvr.
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b) Csvr = 47 µF
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c) Csvr = 100 µF
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Better pop-on performance is obtained with higher
Csvr values (the recommended range is from 22µF
to 220µF).
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The turn-on delay (during which the amplifier is in
mute condition) is a function essentially of : Cout,
Csvr. Being:
T1 ≈ 120 · Cout
T2 ≈ 1200 · Csvr
The turn-on delay is given by:
T1+T2 STEREO
T2 BRIDGE
The best performance is obtained by driving the stby pin with a ramp having a slope slower than 2V/
ms.
5.3 TURN-OFF
A turn-off pop can occur if the st-by pin goes low
with a short time constant (this can occur if other
car radio sections, preamplifiers,radio.. are supplied through the same st-by switch).
This pop is due to the fast switch-off of the internal
current generator of the amplifier.
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TDA7350A
If the voltage present across the load becomes rapidly zero (due to the fast switch off) a small pop occurs,
depending also on Cout,Rload.
The parameters that set the switch off time constant of the st-by pin are:
■
the st-by capacitor (Cst-by)
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the SVR capacitor (Csvr)
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resistors connected from st-by pin to ground (Rext)
The time constant is given by :
T ≈ Csvr · 2000Ω // Rext + Cst-by · 2500Ω // Rext
The suggested time constants are :
T > 120ms with Cout =1000µF, RL = 4ohm,stereo
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T > 170ms with Cout = 2200µF, RL = 4ohm,stereo
If Rext is too low the Csvr can become too high and a different approach may be useful (see next section).
Figg 43, 44 show some types of electronic switches (µP compatible) suitable for supplying the st-by pin (it
is important that Qsw is able to saturate with VCE ≤ 150mV).
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Also for turn off pop the bridge configuration is superior, in particular the st-by pin can go low faster.
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5.4 Global Approach to Solving Pop Problem by Using the Muting/Turn On Delay Function
In the real case turn-on and turn-off pop problems are generated not only by the power amplifier, but also
(very often) by preamplifiers,tone controls, radios etc. and transmitted by the power amplifier to the loudspeaker.
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A simple approach to solving these problems is to use the mute characteristics of the TDA7350A. If the
SVR pin is at a voltage below 1.5 V, the mute attenuation (typ)is 30dB .The amplifier is in play mode when
Vsvr overcomes 3.5 V.
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With the circuit of fig 45 we can mute the amplifier for a time Ton after switch-on and for a time Toff after
switch-off. During this period the circuitry that precedes the power amplifier can produce spurious spikes
that are not transmitted to the loudspeaker.
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This can give back a very simple design of this circuitry from the pop point of view. A timing diagram of
this circuit is illustrated in fig 46.
Other advantages of this circuit are:
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– A reduced time constant allowance of stand-by pin turn off. Consequently it is possible to drive all the
car-radio with the signal that drives this pin.
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– A better turn-off noise with signal on the output. To drive two stereo amplifiers with this circuit it is
possible to use the circuit of fig 47.
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Figure 43.
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TDA7350A
Figure 44.
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Figure 45.
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Figure 46.
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TDA7350A
Figure 47.
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5.5 Balance Input In Bridge Configuration
A helpful characteristic of the TDA7350A is that, in bridge configuration, a signal present on both the input
capacitors is amplified by the same amount and it is present in phase at the outputs, so this signal does
not produce effects on the load.The typical value of CMRR is 46 dB.
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Looking at fig 48, we can see that a noise signal from the ground of the power amplifier to the ground of
the hypothetical preamplifier is amplified of a factor equal to the gain of the amplifier (2 · Gv). Using a configuration of fig. 49 the same ground noise is present at the output multiplied by the factor 2 · Gv/200.
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This means less distortion,less noise (e.g. motor cassette noise ) and/or a simplification of the layout of
PC board.
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The only limitation of this balanced input is the maximum amplitude of common mode signals (few tens of
millivolt) to avoid a loss of output power due to the common mode signal on the output, but in a large number of cases this signal is within this range.
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5.6 High Gain, Low Noise Application
The following section describes a flexible preamplifier having the purpose to increase the gain of the
TDA7350A.
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Figure 48.
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Figure 49.
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A two transistor network (fig. 50) has been adopted whose components can be changed in order to
achieve the desired gain without affecting the good performances of the audio amplifier itself.
The recommended values for 40 dB overall gain are :
Table 6.
Resistance
Stereo
Stereo
R1
10KΩ
10KΩ
R2
4.3KΩ
16KΩ
R3
10KΩ
24KΩ
R4
50KΩ
50KΩ
)
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Figure 50.
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TDA7350A
6
Package Information
Figure 51. Multiwatt11 (Vertical) Mechanical Data & Package Dimensions
mm
DIM.
MIN.
TYP.
inch
MAX.
MIN.
TYP.
5
0.197
B
2.65
0.104
C
1.6
D
OUTLINE AND
MECHANICAL DATA
MAX.
A
0.063
1
0.039
E
0.49
0.55
0.019
F
0.88
0.95
0.035
0.022
G
1.45
1.7
1.95
0.057
0.067
0.077
G1
16.75
17
17.25
0.659
0.669
0.679
H1
19.6
0.037
)
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0.772
H2
20.2
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0.795
L
21.9
22.2
22.5
0.862
0.874
0.886
L1
21.7
22.1
22.5
0.854
0.87
0.886
L2
17.4
18.1
0.685
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
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0.713
L7
2.65
2.9
0.104
M
4.25
4.55
4.85
0.167
0.179
0.191
M1
4.73
5.08
5.43
0.186
0.200
0.214
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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
)-
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Multiwatt11 (Vertical)
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0.152
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0016035 H
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Table 7. Revision History
Date
Revision
February 2005
1
Description of Changes
First Issue
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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. Specifications 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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