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TDA7350A
February 2005
1 General Features
■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
2 Description
The TDA7350A is a new technology class AB Au-
dio Power Amplifier in the Multiwatt® package de-
signed for car radio applications.
Thanks to the fully complementary PNP/NPN out-
put configuration the high power performance of
the TDA7350A is obtained without bootstrap ca-
pacitors.
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.
22W BRIDGE-STEREO AMPLIFIER FOR CAR RADIO
Figure 2. Application Circuit (Bridge)
Rev. 1
Fi
gure 1.
P
ac
k
age
Table 1. Order Codes
Part Number Package
TDA7350A Multiwatt11
Multiwatt11
TDA7350A
2/23
Figure 3. Pin connection (Top view)
Table 2. Absolute Maximum Ratings
Table 3. Thermal Data
Symbol Parameter Value Unit
V
S
Operating Supply Voltage 18 V
V
S
DC Supply Voltage 28 V
V
S
Peak Supply Voltage (t = 50ms) 40 V
I
O
Output Peak Current (non rep. t = 100µs) 5 A
I
O
Output Peak Current (rep. freq. > 10Hz) 4 A
P
tot
Power Dissipation at T
case
= 85°C 36 W
T
stg
, T
j
Storage and Junction Temperature -40 to 150 °C
Symbol Parameter Value Unit
R
thj-case
Thermal Resistance Junction-case Max. 1.8 °C/W
Table 4. Electrical Characteristcs
(Refer to the test circuits, T
amb
= 25°C, V
S
= 14.4V, f = 1KHz unless otherwise specified)
Symbol Parameter Test Condition Min. Typ. Max. Unit
V
S
Supply Voltage Range 8 18 V
I
d
Total Quiescent Drain Current stereo configuration 120 mA
A
SB
Stand-by attenuation 60 80 dB
I
SB
Stand-by Current 100 µA
T
sd
Thermal Shut-down Junction
Temperature
150 °C
3/23
TDA7350A
(*) Curve A
(**) 22Hz to 22KHz
STEREO
P
o
Output Power (each channel) d = 10%
R
L
= 2Ω
R
L
= 3.2Ω
R
L
= 4Ω
7
11
8
6.5
W
W
W
d = 10%; V
S
= 13.2V
R
L
= 2Ω
R
L
= 3.2Ω
R
L
= 4Ω
9
6.5
5.5
W
W
W
d Distortion Po = 0.1 to 4W; R
L
= 3.2Ω0.5 %
SVR Supply Voltage Rejection R
g
= 10kΩ f = 100Hz
C3 = 22µF
C3 = 100µF
45 50
57
dB
dB
C
T
Crosstalk f = 1KHz
f = 10KHz
45 55
50
dB
dB
R
I
Input Resistance 30 50 KΩ
G
V
Voltage Gain 27 29 31 dB
G
V
Voltage Gain Match 1 dB
E
IN
Input Noise Voltage R
g
= 50Ω(*)
R
g
= 10KΩ(*)
R
g
= 50Ω(**)
R
g
= 10KΩ(**)
1.5
2
2
2.7
7 µV
µV
µV
µV
BRIDGE
P
o
Output Power d = 10%; R
L
= 4Ω
d = 10%; R
L
= 3.2Ω
16 20
22
W
W
d = 10%; V
S
= 13.2V
R
L
= 4Ω
R
L
= 3.2Ω
17.5
19
W
W
d Distortion P
o
= 0.1 to 10W; R
L
= 4W 1 %
V
OS
Output Offset Voltage 250 mV
SVR Supply Voltage Rejection R
g
= 10kΩ f = 100Hz
C3 = 22µF
C3 = 100µF
45 50
57
dB
dB
R
I
Input Resistance 50 KΩ
G
V
Voltage Gain 33 35 37 dB
E
IN
Input Noise Voltage R
g
= 50Ω(*)
R
g
= 10KΩ(*)
R
g
= 50Ω(**)
R
g
= 10KΩ(**)
2
2.5
2.7
3.2
µV
µV
µV
µV
Table 4. Electrical Characteristcs (continued)
(Refer to the test circuits, T
amb
= 25°C, V
S
= 14.4V, f = 1KHz unless otherwise specified)
Symbol Parameter Test Condition Min. Typ. Max. Unit
TDA7350A
4/23
Figure 4. STEREO Test and Appication Circuit
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
Figure 7. P.C. Board and Layout (BRIDGE) of the circuit of fig. 6
TDA7350A
6/23
Table 5. Recommended Values of the External Components
(ref. to the Stereo Test and Application Circuit)
Component Recommended
Value Purpose Larger than the Recomm.
Value
Smaller than the Recomm.
Value
C1 0.22µF Input
Decoupling (CH1)
——
C2 0.22µF Input Decoupling
(CH2)
——
C3 100µF Supply Voltage
Rejection
Filtering
Capacitor
Longer Turn-On Delay
Time
Worse Supply Voltage
Rejection.
Shorter Turn-On Delay Time
Danger of Noise (POP)
C4 22µF Stand-By
ON/OFF Delay
Delayed Turn-Off by Stand-
By Switch
Danger of Noise (POP)
C5 220µF (min) Supply By-Pass Danger of Oscillations
C6 100nF (min) Supply By-Pass Danger of Oscillations
C7 2200µF Output
Decoupling
CH2
- Decrease of Low Frequency
Cut Off
- Longer Turn On Delay
- Increase of Low Frequency
Cut Off
- Shorter Turn On Delay
Figure 8. Output Power vs. Supply Voltage
(Stereo)
Figure 9. Output Power vs. Supply Voltage
(Stereo)
Figure 10. Output Power vs. Supply Voltage
(Stereo)
Figure 11. Output Power vs. Supply Voltage
(Bridge)
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TDA7350A
Figure 12. Output Power vs. Supply Voltage
(Bridge)
Figure 13. Drain Current vs Supply Voltage
(Stereo)
Figure 14. Distortion vs Output Power
(Stereo)
Figure 15. Distortion vs Output Power
(Stereo)
Figure 16. Distortion vs Output Power
(Stereo)
Figure 17. Distortion vs Output Power
(Bridge)
TDA7350A
8/23
Figure 18. SVR vs. Frequency & C
SVR
(Stereo)
Figure 19. SVR vs. Frequency & C
SVR
;
(Stereo)
Figure 20. SVR vs. Frequency & C
SVR
;
(Bridge)
Figure 21. SVR vs. Frequency & C
SVR
;
(Bridge)
Figure 22. Crosstalk vs. Frequency
(Stereo)
Figure 23. Power Dissipation & Efficiency vs.
Output Power (Stereo)
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TDA7350A
Figure 24. Power Dissipation & Efficiency vs.
Output Power (Stereo)
Figure 25. Power Dissipation & Efficiency vs.
Output Power (Bridge)
Figure 26. Power Dissipation & Efficiency vs.
Output Power (Bridge))
3 Amplifier Organization
The TDA7350A has been developed taking care of
the key concepts of the modern power audio am-
plifier for car radio such as: space and costs sav-
ing 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:
■NO NEED OF BOOTSTRAP CAPACITORS
EVEN AT THE HIGHEST OUTPUT POWER
LEVELS
■ABSOLUTE STABILITY WITHOUT EXTERNAL
COMPENSATION THANKS TO THE NNOVA-
TIVE 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 OP-
TIMIZE SVR
■SILENT MUTE/ST-BY FUNCTION FEATUR-
ING ABSENCE OF POP ON/OFF NOISE
■HIGH SVR
■STEREO/BRIDGE OPERATION WITHOUT
ADDITION OF EXTERNAL COMPONENT
■AC/DC SHORT CIRCUIT PROTECTION (TO
GND, TO V
S
, ACROSS THE LOAD)
■LOUDSPEAKER PROTECTION
■DUMP PROTECTION
■ESD PROTECTION
4 Block Description
4.1 Polarization
The device is organized with the gain resistors di-
rectly connected to the signal ground pin i.e. with-
out gain capacitors (fig. 27).
The non inverting inputs of the amplifiers are con-
nected to the SVR pin by means of resistor divid-
ers, equal to the feedback networks. This allows
the outputs to track the SVR pin which is sufficient-
ly slow to avoid audible turn-on and turn-off tran-
sients.
4.2 SVR
The voltage ripple on the outputs is equal to the
one on SVR pin: with appropriate selection of CS-
VR, more than 55dB of ripple rejection can be ob-
tained.
TDA7350A
10/23
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 power-
on 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 cir-
cuits) the device switches on, the SVR capacitor starts charging itself and the output tracks exactly the
SVR pin.
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.
4.4 Stereo/Bridge Switching
There is also no need for external components for changing from stereo to bridge configuration (figg. 27-
30). A simple short circuit between two pins allows phase reversal at one output, yet maintaining the qui-
escent output voltage.
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.
4.6 Stability
The device is provided with an internal compensation wich allows to reach low values of closed loop gain.
In this way better performances on S/N ratio and SVR can be obtained.
Figure 27. Block Diagram; Stereo Configuration
11/23
TDA7350A
Figure 28. Turn-on Delay Circuit
Figure 29. Mute Function Diagram
TDA7350A
12/23
Figure 30. Block Diagram; Bridge Configuration
Figure 31. ICV - PNP Gain vs. I
C
Figure 32. ICV - PNP V
CE(sat)
vs. I
C
Figure 33. ICV - PNP cut-off frequency vs. I
C
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 ex-
pense of external components, namely, the boot-
strap capacitors. The availability of 4A isolated
collector PNP (ICV PNP) adds versatility to the de-
sign. The performance of this component, in terms
of gain, V
CEsat
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
13/23
TDA7350A
of low leakage diodes, too. It guarantees BV
CEO
> 20V and BV
CBO
> 50V both for NPN and PNP transis-
tors. 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 V
CEsat
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
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.
4.8 AMPLIFIER BLOCK DIAGRAM
The block diagram of each voltage amplifier is shown in fig. 36. Regardless of production spread, the cur-
rent 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
Figure 36. Amplifier Block Diagram
TDA7350A
14/23
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 cur-
rents 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.
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.
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
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.
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.
15/23
TDA7350A
Figure 39.
4.9.3 Polarity Inversion
High current (up to 10A) can be handled by the de-
vice with no damage for a longer period than the
blow-out time of a quick 2A fuse (normally con-
nected 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.
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 pro-
tection diodes are included to avoid any damage.
4.10.1DC Voltage
The maximum operating DC voltage for the
TDA7350A is 18V. However the device can with-
stand a DC voltage up to 28V with no damage.
This could occur during winter if two batteries are
series connected to crank the engine.
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 perma-
nent), 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 exces-
sive junction temperature: all happens is that P
o
(and therefore P
tot
) and Id are reduced.
The maximum allowable power dissipation de-
pends upon the size of the external heatsink (i.e.
its thermal resistance); Fig. 40 shows the dissi-
pable power as a function of ambient temperature
for different thermal resistance.
Figure 40. Maximum Allowable Power
Dissipation vs. Ambient Temperature
The TDA7350A guarantees safe operations even
for the loudspeaker in case of accidental shortcir-
cuit.
Whenever a 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.
Figure 41. Restart Circuit
TDA7350A
16/23
5 Application Hints
This section explains briefly how to get the best
from the TDA7350A and presents some applica-
tion 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.
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.
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).
5.2 TURN-ON
Fig. 42 shows the output waveform (before and af-
ter the "A" weighting filter) compared to the value
of C
svr
.
Better pop-on performance is obtained with higher
C
svr
values (the recommended range is from 22µF
to 220µF).
The turn-on delay (during which the amplifier is in
mute condition) is a function essentially of : C
out
,
C
svr
. Being:
T1 ≈ 120 · C
out
T2 ≈ 1200 · C
svr
The turn-on delay is given by:
T1+T2 STEREO
T2 BRIDGE
The best performance is obtained by driving the st-
by pin with a ramp having a slope slower than 2V/
ms.
Figure 42.
a) C
svr
= 22 µF
b) C
svr
= 47 µF
c) C
svr
= 100 µF
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 sup-
plied through the same st-by switch).
This pop is due to the fast switch-off of the internal
current generator of the amplifier.
17/23
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)
■the SVR capacitor (Csvr)
■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 C
out
=1000µF, R
L
= 4ohm,stereo
T > 170ms with C
out
= 2200µF, R
L
= 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 V
CE
≤ 150mV).
Also for turn off pop the bridge configuration is superior, in particular the st-by pin can go low faster.
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 loud-
speaker.
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.
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.
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:
– 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.
– 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.
Figure 43.
TDA7350A
18/23
Figure 44.
Figure 45.
Figure 46.
19/23
TDA7350A
Figure 47.
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.
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 con-
figuration of fig. 49 the same ground noise is present at the output multiplied by the factor 2 · Gv/200.
This means less distortion,less noise (e.g. motor cassette noise ) and/or a simplification of the layout of
PC board.
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 num-
ber of cases this signal is within this range.
5.6 High Gain, Low Noise Application
The following section describes a flexible preamplifier having the purpose to increase the gain of the
TDA7350A.
Figure 48.
Figure 49.
TDA7350A
20/23
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.
Figure 50.
Resistance Stereo Stereo
R1 10KΩ10KΩ
R2 4.3KΩ16KΩ
R3 10KΩ24KΩ
R4 50KΩ50KΩ
21/23
TDA7350A
6 Package Information
Figure 51. Multiwatt11 (Vertical) Mechanical Data & Package Dimensions
OUTLINE AND
MECHANICAL DATA
0016035 H
DIM. mm inch
MIN. TYP. MAX. MIN. TYP. MAX.
A50.197
B 2.65 0.104
C1.60.063
D 1 0.039
E 0.49 0.55 0.019 0.022
F 0.88 0.95 0.035 0.037
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 0.772
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 0.87 0.886
L2 17.4 18.1 0.685 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 4.73 5.08 5.43 0.186 0.200 0.214
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
Multiwatt11 (Vertical)
TDA7350A
22/23
Table 7. Revision History
Date Revision Description of Changes
February 2005 1 First Issue
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.
The ST logo is a registered trademark of STMicroelectronics.
All other names are the property of their respective owners
© 2005 STMicroelectronics - All rights reserved
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TDA7350A
