ST TDA7350A User Manual

TDA7350A
Fi
22W BRIDGE-STEREO AMPLIFIER FOR CAR RADIO

1 General Features

VERY FEW EXTERNAL COMPONENTS
NO BOUCHEROT CELLS
NO BOOSTRAP CAPACITORS
HIGH OUTPUT POWER
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-
gure 1. Package
Multiwatt11

Table 1. Order Codes

Part Number Package
TDA7350A Multiwatt11
dio Power Amplifier in the Multiwatt® package de­signed for car radio applications.
Thanks to the fully complementary PNP/NPN out­put configuration the high power performance of the TDA7350A is obtained without bootstrap ca­pacitors.
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)

February 2005
Rev. 1
1/23
TDA7350A

Figure 3. Pin connection (Top view)

Table 2. Absolute Maximum Ratings

Symbol Parameter Value Unit
V
V
V
I
O
I
O
P
tot
T
stg
Operating Supply Voltage 18 V
S
DC Supply Voltage 28 V
S
Peak Supply Voltage (t = 50ms) 40 V
S
Output Peak Current (non rep. t = 100µs) 5 A
Output Peak Current (rep. freq. > 10Hz) 4 A
Power Dissipation at T
= 85°C 36 W
case
, TjStorage and Junction Temperature -40 to 150 °C

Table 3. Thermal Data

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
Symbol Parameter Test Condition Min. Typ. Max. Unit
V
Supply Voltage Range 8 18 V
S
Total Quiescent Drain Current stereo configuration 120 mA
I
d
A
I
T
Stand-by attenuation 60 80 dB
SB
Stand-by Current 100 µA
SB
Thermal Shut-down Junction
sd
Temperature
= 25°C, VS = 14.4V, f = 1KHz unless otherwise specified)
amb
150 °C
2/23
TDA7350A
Table 4. Electrical Characteristcs (continued)
(Refer to the test circuits, T
Symbol Parameter Test Condition Min. Typ. Max. Unit
STEREO
P
Output Power (each channel) d = 10%
o
d Distortion Po = 0.1 to 4W; R
SVR Supply Voltage Rejection R
Crosstalk f = 1KHz
C
T
RI Input Resistance 30 50 K
Voltage Gain 27 29 31 dB
G
V
Voltage Gain Match 1 dB
G
V
Input Noise Voltage Rg= 50Ω(*)
E
IN
BRIDGE
Output Power d = 10%; RL= 4
P
o
d Distortion P
Output Offset Voltage 250 mV
V
OS
SVR Supply Voltage Rejection R
Input Resistance 50 K
R
I
Voltage Gain 33 35 37 dB
G
V
Input Noise Voltage Rg= 50Ω(*)
E
IN
(*) Curve A (**) 22Hz to 22KHz
= 25°C, VS = 14.4V, f = 1KHz unless otherwise specified)
amb
= 2
R
L
RL= 3.2 R
= 4
L
d = 10%; V R
= 2
L
= 13.2V
S
7
RL= 3.2 R
= 4
L
= 3.2 0.5 %
L
= 10k f = 100Hz
g
C3 = 22µF
45 50
C3 = 100µF
45 55
f = 10KHz
R
= 10KΩ(*)
g
R
= 50Ω(**)
g
Rg= 10KΩ(**)
16 20
d = 10%; R
d = 10%; V
= 3.2
L
= 13.2V
S
RL= 4 R
= 3.2
L
= 0.1 to 10W; RL = 4W 1 %
o
= 10k f = 100Hz
g
C3 = 22µF
45 50
C3 = 100µF
R
= 10KΩ(*)
g
R
= 50Ω(**)
g
Rg= 10KΩ(**)
11
8
6.5
9
6.5
5.5
57
50
1.5 2 2
2.7
22
17.5 19
57
2
2.5
2.7
3.2
7 µV
W W W
W W W
dB dB
dB dB
µV µV µV
W W
W W
dB dB
µV µV µV µV
3/23
TDA7350A

Figure 4. STEREO Test and Appication Circuit

Figure 5. P.C. Board and Layout (STEREO) of the circuit of fig. 4

4/23

Figure 6. BRIDGE Test and Appication Circuit

Figure 7. P.C. Board and Layout (BRIDGE) of the circuit of fig. 6

TDA7350A
5/23
TDA7350A
Table 5. Recommended Values of the External Components
(ref. to the Stereo Test and Application Circuit)
Component
C1 0.22µF Input
C2 0.22µF Input Decoupling
C3 100µF Supply Voltage
C4 22µF Stand-By
C5 220µF (min) Supply By-Pass Danger of Oscillations
C6 100nF (min) Supply By-Pass Danger of Oscillations
C7 2200µF Output
Recommended
Val ue
Purpose
Decoupling (CH1)
(CH2)
Rejection Filtering Capacitor
ON/OFF Delay
Decoupling CH2

Figure 8. Output Power vs. Supply Voltage (Stereo)

Larger than the Recomm.
Value
——
——
Longer Turn-On Delay Time
Delayed Turn-Off by Stand­By Switch
- Decrease of Low Frequency Cut Off
- Longer Turn On Delay
Smaller than the Recomm.
Worse Supply Voltage Rejection. Shorter Turn-On Delay Time Danger of Noise (POP)
Danger of Noise (POP)
- Increase of Low Frequency Cut Off
- Shorter Turn On Delay

Figure 10. Output Power vs. Supply Voltage (Stereo)

Val ue

Figure 9. Output Power vs. Supply Voltage (Stereo)

6/23

Figure 11. Output Power vs. Supply Voltage (Bridge)

TDA7350A

Figure 12. Output Power vs. Supply Voltage (Bridge)

Figure 13. Drain Current vs Supply Voltage (Stereo)

Figure 15. Distortion vs Output Power (Stereo)

Figure 16. Distortion vs Output Power (Stereo)

Figure 14. Distortion vs Output Power (Stereo)

Figure 17. Distortion vs Output Power (Bridge)

7/23
TDA7350A
Figure 18. SVR vs. Frequency & C (Stereo)
Figure 19. SVR vs. Frequency & C (Stereo)
SVR
SVR
Figure 21. SVR vs. Frequency & C
SVR
;
(Bridge)
;

Figure 22. Crosstalk vs. Frequency (Stereo)

Figure 20. SVR vs. Frequency & C (Bridge)
8/23
SVR
;

Figure 23. Power Dissipation & Efficiency vs. Output Power (Stereo)

TDA7350A

Figure 24. Power Dissipation & Efficiency vs. Output Power (Stereo)

Figure 25. 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 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:
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 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
LOUDSPEAKER PROTECTION
DUMP PROTECTION
ESD PROTECTION
, ACROSS THE LOAD)
S

Figure 26. Power Dissipation & Efficiency vs. Output Power (Bridge))

4 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.
9/23
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.
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 qui­escent 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

10/23

Figure 28. Turn-on Delay Circuit

TDA7350A

Figure 29. Mute Function Diagram

11/23
TDA7350A

Figure 30. Block Diagram; Bridge Configuration

Figure 31. ICV - PNP Gain vs. I
Figure 32. ICV - PNP V
CE(sat)
vs. I
C
C
Figure 33. ICV - PNP cut-off frequency vs. I

4.7 OUTPUT STAGE

C
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, V
and cut-off frequency, is shown in
CEsat
fig. 31, 32, 33 respectively. It is realized in a new bipolar technology, characterized by topbottom isolation techniques, allowing the implementation
12/23
TDA7350A
of low leakage diodes, too. It guarantees BV
> 20V and BV
CEO
> 50V both for NPN and PNP transis-
CBO
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
of the output transistors, which are in the range of 0.3 each. Then,
CEsat
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 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

Figure 36. Amplifier Block Diagram

13/23
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.
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.

14/23

Figure 39.

TDA7350A

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.

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.

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.
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 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 P (and therefore P
) and Id are reduced.
tot
The maximum allowable power dissipation de­pends 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 shortcir­cuit.
Whenever a single OUT to GND, OUT to V circuit occurs both the outputs are switched OFF so limiting dangerous DC current flowing through the loudspeaker.

Figure 41. Restart Circuit

o
short
S
15/23
TDA7350A

5 Application Hints

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.
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).

Figure 42.

= 22 µF
a) C
svr
b) C
= 47 µF
svr

5.2 TURN-ON

Fig. 42 shows the output waveform (before and af­ter the "A" weighting filter) compared to the value of C
.
svr
Better pop-on performance is obtained with higher C
values (the recommended range is from 22µF
svr
to 220µF).
The turn-on delay (during which the amplifier is in mute condition) is a function essentially of : C C
. Being:
svr
T1 120 · C
T2 1200 · C
out
svr
out
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.
c) C
= 100 µF
svr
,

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.
16/23
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 · 2000 // Rext + Cst-by · 2500 // Rext
The suggested time constants are :
T > 120ms with C
T > 170ms with C
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
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 loud­speaker.
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.
=1000µF, RL = 4ohm,stereo
out
= 2200µF, RL = 4ohm,stereo
out
150mV).
CE

Figure 43.

17/23
TDA7350A

Figure 44.

Figure 45.

Figure 46.

18/23
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 con­figuration 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 num­ber 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.

19/23
TDA7350A
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
R2
R3
R4

Figure 50.

10K 10K
4.3K 16K
10K 24K
50K 50K
20/23

6 Package Information

Figure 51. Multiwatt11 (Vertical) Mechanical Data & Package Dimensions

TDA7350A
DIM.
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
mm inch
MIN. TYP. MAX. MIN. TYP. MAX.
OUTLINE AND
MECHANICAL DATA
Multiwatt11 (Vertical)
0016035 H
21/23
TDA7350A

Table 7. Revision History

Date Revision Description of Changes
February 2005 1 First Issue
22/23
TDA7350A
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
Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan -
Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America
STMicroelectronics group of companies
www.st.com
23/23
Loading...