MUTING/STAND-BYFUNCTIONS
NO SWITCHON/OFF NOISE
VERYLOW DISTORTION
VERYLOW NOISE
SHORTCIRCUIT PROTECTION
THERMALSHUTDOWN
CLIPDETECTOR
MODULARITY (MORE DEVICES CAN BE
EASILY CONNECTED IN PARALLEL TO
DRIVE VERYLOW IMPEDANCES)
DESCRIPTION
The TDA7293 is a monolithic integrated circuit in
Multiwatt15 package, intended for use as audio
class AB amplifier in Hi-Fi field applications
(Home Stereo, self powered loudspeakers, Top-
Figure 1: Typical Applicationand Test Circuit
MULTIPOWER BCD TECHNOLOGY
Multiwatt15
ORDERING NUMBER: TDA7293V
class TV). Thanks to the wide voltage range and
to the high out current capability it is able to supply the highest powerinto both4Ω and 8Ω loads.
The built in muting function with turn on delay
simplifiesthe remote operation avoiding switching
on-off noises.
Parallel mode is made possible by connecting
more device through of pin11. High output power
can be deliveredto verylow impedance loads, so
optimizingthe thermal dissipation ofthe system.
VMUTE
VSTBY
December1999
C7 100nFC6 1000µF
R3 22K
C2
R2
22µF
680Ω
C1 470nF
R1 22K
R5 10K
R4 22K
C3 10µFC410µF
IN-2
IN+
3
4
SGND
(**)
10
MUTE
9
STBY
(*) see Application
(**) for SLAVE function
note
MUTE
STBY
1
STBY-GND
+Vs
BUFFER DRIVER
713
11
-
+
THERMAL
SHUTDOWN
-Vs-PWVs
C9 100nFC8 1000µF
PROTECTION
158
-Vs
+PWVs+Vs
S/C
14
12
6
5
D97AU805A
OUT
BOOT
LOADER
C5
22µF
BOOTSTRAP
CLIP DET
(*)
VCLIP
1/13
TDA7293
PIN CONNECTION (Top view)
TAB CONNECTED TO PIN 8
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
D97AU806
-VS(POWER)
OUT
(POWER)
+V
S
BOOTSTRAP LOADER
BUFFER DRIVER
MUTE
STAND-BY
-V
(SIGNAL)
S
+VS(SIGNAL)
BOOTSTRAP
CLIP AND SHORT CIRCUIT DETECTOR
SIGNAL GROUND
NON INVERTING INPUT
INVERTING INPUT
STAND-BY GND
APPLICATIONSUGGESTIONS(seeTest andApplication Circuitsof the Fig. 1)
The recommendedvalues of the external components are those shown on the application circuit of Figure 1. Different valuescan be used; the followingtable can help the designer.
COMPONENTSSUGGESTED VALUEPURPOSE
LARGER THAN
SUGGESTED
R1 (*)22kINPUT RESISTANCEINCREASE INPUT
IMPEDANCE
R2680
Ω
CLOSED LOOP GAIN
DECREASE OF GAIN INCREASE OF GAIN
SMALLER THAN
SUGGESTED
DECREASE INPUT
IMPEDANCE
SET TO 30dB (**)
R3 (*)22kINCREASE OF GAIN DECREASE OF GAIN
R422kST-BY TIME
CONSTANT
LARGER ST-BY
ON/OFF TIME
SMALLER ST-BY
ON/OFF TIME;
POP NOISE
R510kMUTE TIME
CONSTANT
C10.47µFINPUT DC
DECOUPLING
LARGER MUTE
ON/OFF TIME
SMALLER MUTE
ON/OFF TIME
HIGHER LOW
FREQUENCY
CUTOFF
C222µFFEEDBACK DC
DECOUPLING
HIGHER LOW
FREQUENCY
CUTOFF
C310µFMUTE TIME
CONSTANT
C410µFST-BY TIME
CONSTANT
LARGER MUTE
ON/OFF TIME
LARGER ST-BY
ON/OFF TIME
SMALLER MUTE
ON/OFF TIME
SMALLER ST-BY
ON/OFF TIME;
POP NOISE
C522µFXN (***)BOOTSTRAPPINGSIGNAL
C6, C81000µFSUPPLY VOLTAGE
C7, C90.1µFSUPPLY VOLTAGE
(*) R1 = R3 for pop optimization
(**) Closed Loop Gain has to be≥26dB
(***) Multiplay this value for thenumber of modular part connected
Slave function:pin 4 (Ref to pin8 -VS)
+3V
-V
S
+1V
-V
S
-V
S
MASTER
UNDEFINED
SLAVE
D98AU821
DEGRADATION AT
LOW FREQUENCY
BYPASS
DANGER OF
BYPASS
OSCILLATION
Note:
If in the application, the speakers are connected
via long wires, it is a good rule to add between
the output and GND, a BoucherotCell, in order to
avoid dangerous spurious oscillations when the
speakersterminal are shorted.
The suggested Boucherot Resistor is 3.9Ω/2W
and the capacitoris 1µF.
5/13
TDA7293
INTRODUCTION
In consumer electronics, an increasing demand
has arisen for very high power monolithic audio
amplifiers able to match, with a low cost, the performance obtained from the best discrete designs.
The task of realizing this linear integrated circuit
in conventional bipolar technology is made extremely difficult by the occurence of 2nd breakdown phoenomenon. It limits the safe operating
area (SOA) of the power devices, and, as a consequence, the maximum attainable output power,
especiallyin presenceof highlyreactive loads.
Moreover, full exploitation of the SOA translates
into a substantial increase in circuit and layout
complexity due to the need of sophisticated protection circuits.
To overcome these substantial drawbacks, the
use of power MOS devices, which are immune
from secondarybreakdown is highly desirable.
The device described has therefore been developed in a mixed bipolar-MOS high voltage technology called BCDII100/120.
1) Output Stage
The main design task in developpinga power operational amplifier, independently of the technology used, is that of realization of the output stage.
The solution shown as a principle shematic by
Fig3 represents the DMOSunity - gain output
buffer of the TDA7293.
This large-signal, high-power buffer must be capable of handling extremely high current and voltage levels while maintaining acceptably low harmonicdistortion andgoodbehaviour over
frequency response; moreover, an accurate control of quiescentcurrent is required.
A local linearizing feedback, provided by differential amplifier A, is used to fullfilthe above requirements, allowing a simple and effective quiescent
currentsetting.
Proper biasing of the power output transistors
alone is howevernot enough to guarantee the absenceof crossoverdistortion.
While a linearization of the DC transfer characteristic of the stage is obtained, the dynamic behaviour of the systemmust be taken into account.
A significant aid in keeping the distortion contributed by the final stage as low as possible is provided by the compensation scheme, which exploits the direct connection of the Miller capacitor
at the amplifier’s output to introduce a local AC
feedbackpath enclosing the outputstage itself.
2) Protections
In designing a power IC, particular attention must
be reserved to the circuits devoted to protection
of the device from short circuit or overload conditions.
Due to the absence of the 2nd breakdown phenomenon, the SOA of the power DMOS transistors is delimited only by a maximum dissipation
curve dependent on the duration of the applied
stimulus.
In order to fully exploit the capabilities of the
power transistors, the protection scheme implemented in this device combines a conventional
SOA protection circuit with a novellocal temperature sensing technique which ” dynamically” controls the maximumdissipation.
Figure 3: PrincipleSchematic of a DMOSunity-gainbuffer.
6/13
Figure 4: Turn ON/OFFSuggestedSequence
+Vs
(V)
+40
-40
-Vs
VIN
(mV)
V
ST-BY
PIN #9
(V)
5V
TDA7293
V
MUTE
PIN #10
(V)
IQ
(mA)
V
OUT
(V)
5V
OFF
ST-BY
PLAY
MUTEMUTE
In addition to the overload protection described
above, the device features a thermal shutdown
circuit which initially puts the device into a muting
state (@ Tj = 150
Tj = 160
o
C).
o
C) and then into stand-by (@
Full protectionagainst electrostaticdischarges on
every pin is included.
Figure 5:
SingleSignal ST-BY/MUTEControl
Circuit
MUTESTBY
MUTE/
ST-BY
20K
10K30K
1N4148
10µF10µF
D93AU014
3) OtherFeatures
The device is provided with both stand-by and
ST-BYOFF
D98AU817
mute functions, independently driven by two
CMOSlogic compatible input pins.
The circuits dedicated to the switching on and off
of the amplifier have been carefully optimized to
avoid any kindof uncontrolledaudible transient at
the output.
The sequence that we recommend during the
ON/OFFtransientsis shown by Figure 4.
The application of figure 5 shows thepossibility of
using only one command for both st-by and mute
functions. On both the pins, the maximum applicable range corresponds to the operating supply
voltage.
APPLICATION INFORMATION
HIGH-EFFICIENCY
Constraints of implementinghigh power solutions
are the power dissipation and the size of the
power supply. These are both due to the low efficiency of conventional AB class amplifier approaches.
Here below (figure 6) is described a circuit proposal for a high efficiency amplifier which can be
adopted for both HI-FI and CAR-RADIO applications.
7/13
TDA7293
The TDA7293 is a monolithic MOS power amplifier which can be operated at 100V supplyvoltage
(120V with no signal applied) while delivering output currentsup to ±6.5 A.
This allows the use of this device as a very high
power amplifier (up to 180W as peak power with
T.H.D.=10 % and Rl = 4 Ohm);the only drawback
is the power dissipation, hardly manageable in
the above power range.
The typical junction-to-case thermal resistance of
the TDA7293 is 1
avoid that, in worst case conditions, the chip temperature exceedes150
of the heatsink must be 0.038
bient temperatureof 50
o
C/W (max= 1.5oC/W). To
o
C, the thermal resistance
o
o
C).
C/W (@ max am-
As the above value is pratically unreachable; a
high efficiency system is needed in those cases
where the continuousRMS output power is higher
than 50-60 W.
The TDA7293 was designed to work also in
higher efficiencyway.
For this reason there are four power supply pins:
two intended for the signal part and two for the
power part.
T1 and T2 are two power transistors that only
operate when the output power reaches a certain
threshold (e.g. 20 W). If the output power increases, these transistors are switched on during
the portion of the signal where more output voltage swing is needed, thus ”bootstrapping” the
power supply pins(#13 and #15).
The current generators formed by T4, T7, zener
diodes Z1, Z2 and resistors R7,R8 define the
minimum drop across the power MOS transistors
of the TDA7293. L1, L2, L3 and the snubbersC9,
R1 and C10, R2 stabilize the loops formed by the
”bootstrap” circuits and the output stage of the
TDA7293.
By considering again a maximum average
output power (music signal) of 20W, in case
of the high efficiency application, the thermal
resistance value needed from the heatsink is
o
C/W (Vs =±50 V and Rl= 8 Ohm).
2.2
All components (TDA7293 and power transistors T1 and T2) can be placed on a 1.5
o
C/W
heatsink, with the power darlingtons electrically
insulatedfrom the heatsink.
Since the total power dissipation is less than that
of a usual class AB amplifier, additional cost savings can be obtained while optimizing the power
supply, even witha high heatsink.
BRIDGE APPLICATION
Another application suggestion is the BRIDGE
configuration,where two TDA7293 are used.
In this application, the value of the load must not
be lower than 8 Ohm for dissipation and current
capability reasons.
A suitable field of application includes HI-FI/TV
subwoofersrealizations.
The main advantagesoffered by this solutionare:
- High power performanceswith limited supply
voltagelevel.
- Considerablyhigh output power even with high
loadvalues (i.e. 16 Ohm).
With Rl= 8 Ohm, Vs = ±25V the maximum output
power obtainable is 150 W, while with Rl=16
Ohm,Vs = ±40V the maximumPout is 200W.
APPLICATION NOTE: (ref. fig. 7)
ModularApplication (moreDevices in Parallel)
The use of the modular application lets very high
power be delivered to very low impedance loads.
The modular application implies one device to act
as a master and the others as slaves.
The slave power stages are driven by the master
device and work in parallel all together, while the
input and the gain stages of the slave device are
disabled, the figure below shows the connections
required to configure two devices to work together.
The master chip connections are the same as
the normal single ones.
The outputs can be connected together with-
out the need of any ballast resistance.
The slave SGND pin must be tied to the negative supply.
The slave ST-BY pin must be connected to
ST-BYpin.
The bootstrap lines must be connected together and the bootstrap capacitor must be increased: for N devices the boostrap capacitor
must be 22µF times N.
The slave Mute and IN-pinsmust be grounded.
THE BOOTSTRAP CAPACITOR
For compatibility purpose with the previous devices of the family, the boostrap capacitor can be
connectedboth between the bootstrappin (6) and
the output pin (14) or between the boostrap pin
(6) and the bootstraploader pin (12).
When the bootcap is connected between pin 6
and 14, the maximum supply voltage in presence
of output signal is limited to 100V, due the bootstrapcapacitor overvoltage.
When the bootcap is connected between pins 6
and 12 the maximum supply voltageextend to the
full voltagethat thetechnologycan stand:120V.
This is accomplished by the clamp introduced at
the bootstrap loader pin (12): this pin follows the
output voltage up to 100V and remains clamped
at 100V for higher output voltages. This feature
lets the output voltage swing up to a gate-source
voltagefrom the positive supply (V
Informationfurnishedis believed to be accurate and reliable. However , STMicroelectronics assumes no respons i bilit yfor the consequences
of use of such informationnor for any infringement of patents or otherrights of third parties which may result from its use. No license is
grantedby implicationor otherwise underany patentor patentrightsof STMicroelectronics. Specification mentioned inthispublicationare
subject tochange withoutnotice. This publicationsupersedes and replacesall informationpreviouslysupplied.STMicroelectronicsproducts
are notauthorizedforuse as cri tical compo nent sinlife suppor tdevicesor systems without expresswritt enapprovalof STMicroelectronics.
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The ST logois a registeredtrademarkof STMicroelectronics
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13/13
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