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TDA7295S
80V
TDA7295S80V - 80W DMOS AUDIO AMPLIFIER WITH MUTE/ST-BY
VERY HIGH OPERATING VOLTAGE RANGE
(±40V)
DMOS POWER STAGE
HIGH OUTPUT POWER (80W @ THD = 10%,
MUSIC POWER)
MUTING/STAND-BY FUNCTIONS
NO SWITCH ON/OFF NOISE
VERY LOW DISTORTION
VERY LOW NOISE
SHORT CIRCUIT PROTECTION
THERMAL SHUTDOWN
CLIP DETECTOR
MODULARITY (MORE DEVICES CAN BE
EASILY CONNECTED IN PARALLEL TO
DRIVE VERY LOW IMPEDANCES)
DESCRIPTIONThe TDA7295S 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-
class TV). Thanks to the wide voltage range and
to the high out current capability it is able to sup-
ply the highest power into both 4Ω and 8Ω loads.
The built in muting function with turn on delay
simplifies the remote operation avoiding switching
on-off noises.
Parallel mode is made possible by connecting
more device through of pin11. High output power
can be delivered to very low impedance loads, so
optimizing the thermal dissipation of the system.
Figure 1: Typical Application and Test Circuit
ABSOLUTE MAXIMUM RATINGS
PIN CONNECTION (Top view)
QUICK REFERENCE DATA
THERMAL DATA
TDA7295S2/13
ELECTRICAL CHARACTERISTICS (Refer to the Test Circuit VS = ±30V, RL = 8Ω, GV = 30dB;Rg = 50 Ω; Tamb = 25°C, f = 1 kHz; unless otherwise specified).
Note (*):MUSIC POWER is the maximal power which the amplifier is capable of producing across the rated load resistance (regardless of non linearity)
1 sec after the application of a sinusoidal input signal of frequency 1KHz.
Note (**): Tested with optimized Application Board (see fig. 2)
Note (***): Limited by the max. allowable out current
TDA7295S3/13
Figure 2: Typical Application P.C. Board and Component Layout (scale 1:1)
TDA7295S4/13
APPLICATION SUGGESTIONS (see Test and Application Circuits of the Fig. 1)The recommended values of the external components are those shown on the application circuit of Fig-
ure 1. Different values can be used; the following table can help the designer.
(*) R1 = R3 for pop optimization
(**) Closed Loop Gain has to be ≥ 26dB
(***) Multiply this value for the number of modular part connected
Slave function: pin 4 (Ref to pin 8 -VS) 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 Boucherot Cell, in order to
avoid dangerous spurious oscillations when the
speakers terminal are shorted.
The suggested Boucherot Resistor is 3.9Ω/2W
and the capacitor is 1μF.
TDA7295S5/13
INTRODUCTIONIn consumer electronics, an increasing demand
has arisen for very high power monolithic audio
amplifiers able to match, with a low cost, the per-
formance obtained from the best discrete de-
signs.
The task of realizing this linear integrated circuit
in conventional bipolar technology is made ex-
tremely difficult by the occurence of 2nd break-
down phoenomenon. It limits the safe operating
area (SOA) of the power devices, and, as a con-
sequence, the maximum attainable output power,
especially in presence of highly reactive loads.
Moreover, full exploitation of the SOA translates
into a substantial increase in circuit and layout
complexity due to the need of sophisticated pro-
tection circuits.
To overcome these substantial drawbacks, the
use of power MOS devices, which are immune
from secondary breakdown is highly desirable.
The device described has therefore been devel-
oped in a mixed bipolar-MOS high voltage tech-
nology called BCDII 100.
1) Output StageThe main design task in developping a power op-
erational amplifier, independently of the technol-
ogy used, is that of realization of the output stage.
The solution shown as a principle shematic by
Fig3 represents the DMOS unity - gain output
buffer of the TDA7295S.
This large-signal, high-power buffer must be ca-
pable of handling extremely high current and volt-
age levels while maintaining acceptably low har-
monic distortion and good behaviour over
frequency response; moreover, an accurate con-
trol of quiescent current is required.
A local linearizing feedback, provided by differen-
tial amplifier A, is used to fullfil the above require-
ments, allowing a simple and effective quiescent
current setting.
Proper biasing of the power output transistors
alone is however not enough to guarantee the ab-
sence of crossover distortion.
While a linearization of the DC transfer charac-
teristic of the stage is obtained, the dynamic be-
haviour of the system must be taken into account.
A significant aid in keeping the distortion contrib-
uted by the final stage as low as possible is pro-
vided by the compensation scheme, which ex-
ploits the direct connection of the Miller capacitor
at the amplifier’s output to introduce a local AC
feedback path enclosing the output stage itself.
2) ProtectionsIn designing a power IC, particular attention must
be reserved to the circuits devoted to protection
of the device from short circuit or overload condi-
tions.
Due to the absence of the 2nd breakdown phe-
nomenon, the SOA of the power DMOS transis-
tors 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 imple-
mented in this device combines a conventional
SOA protection circuit with a novel local tempera-
ture sensing technique which " dynamically" con-
trols the maximum dissipation.
Figure 3: Principle Schematic of a DMOS unity-gain buffer.
TDA7295S6/13
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 o C) and then into stand-by (@
Tj = 160 oC).
Full protection against electrostatic discharges on
every pin is included.
3) Other Features The device is provided with both stand-by and
mute functions, independently driven by two
CMOS logic compatible input pins.
The circuits dedicated to the switching on and off
of the amplifier have been carefully optimized to
avoid any kind of uncontrolled audible transient at
the output.
The sequence that we recommend during the
ON/OFF transients is shown by Figure 4.
The application of figure 5 shows the possibility of
using only one command for both st-by and mute
functions. On both the pins, the maximum appli-
cable range corresponds to the operating supply
voltage.
APPLICATION INFORMATIONHIGH-EFFICIENCY
Constraints of implementing high power solutions
are the power dissipation and the size of the
power supply. These are both due to the low effi-
ciency of conventional AB class amplifier ap-
proaches.
Here below (figure 6) is described a circuit pro-
posal for a high efficiency amplifier which can be
adopted for both HI-FI and CAR-RADIO applica-
tions.
Figure 5: Single Signal ST-BY/MUTE ControlCircuit
Figure 4: Turn ON/OFF Suggested Sequence
TDA7295S7/13
