TS4998 datasheet(24/33 Pages) STMICROELECTRONICS

24 / 33 page

Application information

TS4998

24/33

The efficiency is the ratio between the output power and the power supply:

Equation 6

The maximum theoretical value is reached when Vpeak = VCC, so:

The TS4998 is stereo amplifier so it has two power amplifiers. Each amplifier produces heat

due to its power dissipation. Therefore, the maximum die temperature is the sum of each

amplifier’s maximum power dissipation. It is calculated as follows:

●

Pdiss 1 = Power dissipation of left channel power amplifier

●

Pdiss 2 = Power dissipation of right channel power amplifier

●

Total Pdiss =Pdiss 1 + Pdiss 2 (W)

In most cases, Pdiss 1 = Pdiss 2, giving:

The maximum die temperature allowable for the TS4998 is 150°C. In case of overheating, a

thermal shutdown protection set to 150°C, puts the TS4998 in standby until the temperature

of the die is reduced by about 5°C.

To calculate the maximum ambient temperature Tamb allowable, you need to know:

●

the power supply voltage value, VCC

●

the load resistor value, RL

●

the package type, RTHJA

Example: VCC=5V, RL=8Ω, RTHJAQFN16=85°C/W (with 2-layer PCB with vias).

Using the power dissipation formula given in Equation 5, the maximum dissipated power per

channel is:

Pdissmax = 633mW

And the power dissipated by both channels is:

Total Pdissmax = 2 x Pdissmax = 1266mW

Tamb is calculated as follows:

Equation 7

Therefore, the maximum allowable value for Tamb is:

Tamb = 150 - 85 x 2 x 1.266=42.4°C

If a 4-layer PCB with vias is used, RTHJAQFN16 = 45°C/W and the maximum allowable

value for Tamb in this case is:

Tamb = 150 - 45 x 2 x 1.266 = 93°C

η=

out

supply

------------------- =

πV

peak

4Vcc

--------------------

η= π

----- = 78.5%

TotalP

diss = 2

diss1

42V

π R

---------------------- P

out 2Pout W

()

–

amb

150

° CR

TJHA

TotalP

dissmax

–

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