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

■ 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-

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 KΩ

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= 4Ω

P

o

d Distortion P

Output Offset Voltage 250 mV

V

OS

SVR Supply Voltage Rejection R

Input Resistance 50 KΩ

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

= 2Ω

R

L

RL= 3.2Ω
R

= 4Ω

L

d = 10%; V
R

= 2Ω

L

= 13.2V

S

7

RL= 3.2Ω
R

= 4Ω

L

= 3.2Ω 0.5 %

L

= 10kΩ 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

= 3.2Ω

L

= 13.2V

S

RL= 4Ω
R

= 3.2Ω

L

= 0.1 to 10W; RL = 4W 1 %

o

= 10kΩ 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 0.3Ω 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 · 2000Ω // Rext + Cst-by · 2500Ω // 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.

10KΩ 10KΩ

4.3KΩ 16KΩ

10KΩ 24KΩ

50KΩ 50KΩ

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