The TDA7293 is a monolithic MOS power ampli-
fier which can be operated at 100V supply voltage
(120V with no signal applied) while delivering out-
put currents up 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
o
C/W (max= 1.5
o
C/W). To
avoid that, in worst case conditions, the chip tem-
perature exceedes 150
o
C, the thermal resistance
of the heatsink must be 0.038
o
C/W (@ max am-
bient temperature of 50
o
C).
As the above value is pratically unreachable; a
high efficiency system is needed in those cases
where the continuous RMS output power is higher
than 50-60 W.
The TDA7293 was designed to work also in
higher efficiency way.
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 in-
creases, these transistors are switched on during
the portion of the signal where more output volt-
age 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 snubbers C9,
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
2.2
o
C/W (Vs =
±
50 V and Rl= 8 Ohm).
All components (TDA7293 and power transis-
tors T1 and T2) can be placed on a 1.5
o
C/W
heatsink, with the power darlingtons electrically
insulated from the heatsink.
Since the total power dissipation is less than that
of a usual class AB amplifier, additional cost sav-
ings can be obtained while optimizing the power
supply, even with a 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
subwoofers realizations.
The main advantages offered by this solution are:
- High power performances with limited supply
voltage level.
- Considerably high output power even with high
load values (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 maximum Pout is 200 W.
APPLICATION NOTE: (ref. fig. 7)
Modular Application (more Devices 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 in-
put and the gain stages of the slave device are dis-
abled, the figure below shows the connections re-
quired 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 nega-
tive supply.
The slave ST-BY and MUTE pins must be con-
nected to the master ST-BY and MUTE pins.
The bootstrap lines must be connected to-
gether and the bootstrap capacitor must be in-
creased: for N devices the boostrap capacitor
must be 22
µ
F times N.
The slave IN-pin must be connected to the
negative supply.
THE BOOTSTRAP CAPACITOR
For compatibility purpose with the previous de-
vices of the family, the boostrap capacitor can be
connected both between the bootstrap pin (6) and
the output pin (14) or between the boostrap pin
(6) and the bootstrap loader 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 boot-
strap capacitor overvoltage.
When the bootcap is connected between pins 6
and 12 the maximum supply voltage extend to the
full voltage that the technology can 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
voltage from the positive supply (V
S
-3 to 6V).
TDA7293
8/15
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