TS4984FC Datasheet, PDF (21/30 Pages) STMicroelectronics – 1.2W Stereo Audio Power Amplifier with Active Low Standby Mode

TS4984FC
Application Information
Note:
and the maximum value is obtained when:
-^∂--_∂-^P--_P--^d--_o-ⁱ-^s-_u--^s-_t-- = 0
and its value is:
P_dissmax
=
-²---^V----^c-²--^c--
π²R_L
(W)
This maximum value is only depending on power supply voltage and load values.
The efficiency, η, is the ratio between the output power and the power supply:
η=
----^P-----^o---^u---^t---- = --^π----^V----^P----^E---^A----^K-
P_supply 4V_CC
The maximum theoretical value is reached when V_PEAK = V_CC, so that:
π_{---- = 78.5%}
4
The TS4984 has two independent power amplifiers, and each amplifier produces heat due to its
power dissipation. Therefore, the maximum die temperature is the sum of the each amplifier’s
maximum power dissipation. It is calculated as follows:
P_diss1 = Power dissipation due to the 1st channel power amplifier.
P_diss2 = Power dissipation due to the 2nd channel power amplifier.
Total P_diss = P_diss1 + P_diss2 (W)
In most cases, P_diss1 = P_diss2, giving:
Total P_diss= P_diss1= P_diss2
(W)
or, stated differently:
Total P_diss
=
4_--------2_----V_----C----C--
π R_L
P_out – 2P_out
(W)
4.5
Decoupling the circuit
Two capacitors are needed to correctly bypass the TS4984. 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 7kHz) and an
indirect influence on power supply disturbances. With a value for C_S of 1µF, you can expect
similar THD+N performances to those shown in the datasheet. For example:
● In the high frequency region, if C_S is lower than 1µF, it increases THD+N and disturbances
on the power supply rail are less filtered.
● On the other hand, if C_S is higher than 1µF, 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), in the following manner:
● If C_b is lower than 1µF, THD+N increases at lower frequencies and PSRR worsens.
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