Datasheet

Application information TS4990
20/33 Doc ID 9309 Rev 13
Therefore, the power dissipated by each amplifier is:
P
diss
= P
supply
- P
out
(W)
and the maximum value is obtained when:
and its value is:
Note: This maximum value is only dependent on power supply voltage and load values.
The efficiency is the ratio between the output power and the power supply:
The maximum theoretical value is reached when V
PEAK
= V
CC
, so:
4.5 Decoupling of the circuit
Two capacitors are needed to correctly bypass the TS4990: a power supply bypass
capacitor C
s
and a bias voltage bypass capacitor C
b
.
C
s
has particular influence on the THD+N in the high frequency region (above 7 kHz) and
an indirect influence on power supply disturbances. With a value for C
s
of 1 µF, you can
expect THD+N levels similar to those shown in the datasheet.
In the high frequency region, if C
s
is lower than 1 µF, it increases THD+N and disturbances
on the power supply rail are less filtered.
On the other hand, if C
s
is higher than 1 µF, those disturbances on the power supply rail are
more filtered.
C
b
has an influence on THD+N at lower frequencies, but its function is critical to the final
result of PSRR (with input grounded and in the lower frequency region).
If C
b
is lower than 1 µF, THD+N increases at lower frequencies and PSRR worsens.
If C
b
is higher than 1 µF, the benefit on THD+N at lower frequencies is small, but the benefit
to PSRR is substantial.
Note that C
in
has a non-negligible effect on PSRR at lower frequencies. The lower the value
of C
in
, the higher the PSRR.
P
diss
22V
CC
π R
L
----------------------
P
out
P
out
–=
δP
diss
δP
out
------------------
= 0
P
diss
max
2V
CC
2
π
2
R
L
-------------- -
(W)=
η =
P
out
P
supply
-------------------
=
πV
PEAK
4V
CC
-----------------------
π
4
-----
= 78.5%