TS4994 datasheet(24/31 Pages) STMICROELECTRONICS

24 / 31 page

TS4994

Application Information

24/31

4.6 Power dissipation and efficiency

Assumptions:

l Load voltage and current are sinusoidal (Vout and Iout)

l Supply voltage is a pure DC source (Vcc)

Regarding the load we have:

and

Therefore, the average current delivered by the supply voltage is:

The power delivered by the supply voltage is:

Psupply = Vcc IccAVG (W)

Then, the power dissipated by each amplifier is

Pdiss = Psupply - Pout (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 Vpeak = Vcc, so

out = V PEAK sinω t (V)

out =

out

R L

-------------- (A)

out =

VPE AK

2RL

---------------------- (W)

ICC

AVG

= 2

VPEAK

πRL

-------------------- (A)

diss

22V

π R

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

out Pou t

–

∂Pdiss

∂P

out

---------------------- = 0

)

(

Vcc

max

Pdiss

η =

out

supply

--------------------- = π

VPEAK

4VCC

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

----- = 78.5%

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