TS4972IJT STMicroelectronics, TS4972IJT Datasheet - Page 21

• Manufacturer Part Number: TS4972IJT
• Description: 1.2W POWER AUDIO AMPLIFIER WITH STANDBY MODE ACTI
• Manufacturer: STMicroelectronics

Hypothesis :
(Vout and Iout)
• Supply voltage is a pure DC source (Vcc)
Regarding the load we have:
and
and
Then, the average current delivered by the supply
voltage is:
The power delivered by the supply voltage is
Psupply = Vcc Icc
Then, the power dissipated by the amplifier is
Pdiss = Psupply - Pout (W)
and the maximum value is obtained when:
Remark : This maximum value is only depending
on power supply voltage and load values.
The efficiency is the ratio between the output
power and the power supply
• Voltage and current in the load are sinusoidal
and its value is:
Power dissipation and efficiency
P
di ss
=
Pdiss
2 2 Vcc
---------------------- P
V
I
CC
P
O UT
=
R
max
O U T
I
AVG
OU T
AVG
L
----------------------- - =
Psup ply
= V
--------------------- - = 0
P
Pdiss
=
(W)
O UT
P
= 2
=
PEAK
V
---------------------- (W)
OU T
2
OU T
V
---------------- - (A)
Vcc
P E A K
2
2 R
OU T
R
V
------------------- - (A)
R
P E A K
L
L
sin t (V)
L
2
–
R
---------------------- -
2
(
P
L
4V
W
V
O UT
P E A K
)
C C
(W)
The maximum theoretical value is reached when
Vpeak = Vcc, so
Two capacitors are needed to bypass properly the
TS4972, a power supply bypass capacitor Cs and
a bias voltage bypass capacitor Cb.
Cs has especially an influence on the THD+N in
high frequency (above 7kHz) and indirectly on the
power supply disturbances.
With 100µF, you can expect similar THD+N
performances like shown in the datasheet.
If Cs is lower than 100µF, in high frequency
increases, THD+N and disturbances on the power
supply rail are less filtered.
To the contrary, if Cs is higher than 100µF, those
disturbances on the power supply rail are more
filtered.
Cb has an influence on THD+N in lower frequency,
but its function is critical on the final result of PSRR
with input grounded in lower frequency.
If Cb is lower than 1µF, THD+N increase in lower
frequency (see THD+N vs frequency curves) and
the PSRR worsens up
If Cb is higher than 1µF, the benefit on THD+N in
lower frequency is small but the benefit on PSRR
is substantial (see PSRR vs. Cb curve : fig.12).
Note that Cin has a non-negligible effect on PSRR
in lower frequency. Lower is its value, higher is the
PSRR (see fig. 13).
Pop and Click performance is intimately linked
with the size of the input capacitor Cin and the bias
voltage bypass capacitor Cb.
Size of Cin is due to the lower cut-off frequency
and PSRR value requested. Size of Cb is due to
THD+N and PSRR requested always in lower
frequency.
Moreover, Cb determines the speed that the
amplifier turns ON. The slower the speed is, the
softer the turn ON noise is.
Decoupling of the circuit
Pop and Click performance
---- - = 78.5%
4
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