TS4974_07 Datasheet, PDF (18/25 Pages) STMicroelectronics – 1W differential audio power amplifier with up/down digital volume control pins

Application information
TS4974
and the maximum value is obtained when:
∂_----P_----d_----i_-s_----s_---
∂P_out
=
0
and its value is:
Equation 3
Pdiss max
=
2 Vcc²
π²R_L
(W)
Note: This maximum value is only dependent on the power supply voltage and load
values.
The efficiency is the ratio between the output power and the power supply:
Equation 4
η=
-----^P----^o---^u---^t---
P_supply
=
--^π----^V----^p---^e---^a---^k-
4V_CC
The maximum theoretical value is reached when V_peak = V_CC, so:
η=
π_----
4
=
78.5%
The maximum die temperature allowable for the TS4974 is 125°C. However, in case of
overheating, a thermal shutdown set to 150° C, puts the TS4974 in standby until the
temperature of the die is reduced by about 5° C.
To calculate the maximum ambient temperature T_amb allowable, you need to know:
● Power supply voltage value, V_CC
● Load resistor value, R_L
● The package type, R_THJA
Example: V_CC=5 V, R_L=8 Ω, R_THJAflip-chip=80° C/W (125 mm² copper heatsink).
Using the power dissipation formula given above in Equation 3 this gives a result of:
P_dissmax = 633mW
T_amb is calculated as follows:
Equation 5
T_amb= 125° C – R_TJHA × P_dissmax
Therefore, the maximum allowable value for T_amb is:
T_amb = 125-80x0.633 = 74.3°C
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