TS4994 ST Microelectronics, Inc., TS4994 Datasheet - Page 25

• Manufacturer Part Number: TS4994
• Description: 1.2W Differential Input Audio Power Amplifier With Selectable Standby
• Manufacturer: ST Microelectronics, Inc.

Application Information
4.6 Power dissipation and efficiency
Assumptions:
Regarding the load we have:
and
and
Therefore, the average current delivered by the
supply voltage is:
The power delivered by the supply voltage is:
Then, the power dissipated by each amplifier is
P
and the maximum value is obtained when:
4.7 Decoupling of the circuit
Two capacitors are needed to correctly bypass
the TS4994. A power supply bypass capacitor C
and a bias voltage bypass capacitor C
C
high frequency region (above 7kHz) and an
indirect influence on power supply disturbances.
With a value for C
diss
S
l
l
has particular influence on the THD+N in the
Load voltage and current are sinusoidal (V
and I
Supply voltage is a pure DC source (V
= P
supply
P
out
diss
)
I
P
- P
V
CC
=
supply
P
out
out
out
S
2 2V
-------------------- - P
AVG
I
out
of 1µF, you can expect similar
= V
--------------------- - = 0
(W)
=
Pdiss
= Vcc Icc
= 2
=
R
P
V
---------------------- (W)
PEAK
CC
out
L
V
------------- (A)
P E A K
2R
R
out
V
------------------- - (A)
L
P E A K
sin t (V)
L
R
2
o ut
AVG
L
–
(W)
P
out
B
.
cc
)
out
S
and its value is:
Note: This maximum value is only dependent on power
The efficiency is the ratio between the output
power and the power supply
The maximum theoretical value is reached when
Vpeak = Vcc, so
The maximum die temperature allowable for the
TS4994
overheating, a thermal shutdown set to 150°C,
puts the TS4994 in standby until the temperature
of the die is reduced by about 5°C.
To calculate the maximum ambient temperature
T
Example:
Chip=100°C/W (100mm
We calculate P
With
T
THD+N performances to those shown in the
datasheet.
In the high frequency region, if C
1µF, it increases THD+N and disturbances on the
power supply rail are less filtered.
On the other hand, if C
disturbances on the power supply rail are more
filtered.
AMB
AMB
l
l
l
Power supply Voltage value, Vcc
Load resistor value, RL
The package type, RTH
supply voltage and load values.
allowable, we need to know:
= 125-100x0.633=61.7°C
T
AMB
is
Pdiss
Vcc=5V,
125°C.
dissmax
125
=
max
------------------- =
P
C
---- - = 78.5%
P
supply
4
= 633mW.
out
S
RTH
2
However,
2
is higher than 1µF, those
copper heatsink).
Vcc
2
RL=8
R
JA
JA
L
---------------------- -
2
4V
(
P
V
W
diss
P E A K
C C
S
)
in
is lower than
(
RTH
) C
case
TS4994
JA
25/32
Flip-
of