TS4909

Application information

Doc ID 11972 Rev 9

27/35

The

efficiency is the ratio between the output power and the power supply.

The

maximum theoretical value is reached when V

PEAK

= V

CC

/2, so:

4.4.3

Total power dissipation

The TS4909 is a stereo (dual channel) amplifier. It has two independent 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:

●

P

diss 1

= power dissipation due to the first channel power amplifier (V

out1

).

●

P

diss 2

= power dissipation due to the second channel power amplifier (V

out2

).

●

Total P

diss

=P

diss 1

+P

diss 2

(W)

In most cases, P

diss 1

= P

diss 2

, giving:

Single-ended configuration:

Phantom ground configuration:

4.5

Decoupling of the circuit

Two capacitors are needed to properly bypass the TS4909 — a power supply capacitor C

s

and a bias voltage bypass capacitor C

b

.

C

s

has a strong influence on the THD+N at high frequencies (above 7 kHz) and indirectly on

the power supply disturbances. With 1

μF, you could expect the THD+N performance to be

similar to the values shown in this datasheet. If C

s

is lower than 1

μF, THD+N increases at

high frequencies and disturbances on the power supply rail are less filtered. On the contrary,

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 value is critical on the final result

of PSRR with inputs grounded at lower frequencies.

●

If C

b

is lower than 1

μF, THD+N increases at lower frequencies and the PSRR worsens

(increases).

●

If C

b

is higher than 1

μF, the benefit on THD+N and PSRR in the lower frequency range

is small.

η

P

OUT

P

suppl y

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

πV

P EAK

4V

CC

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

==

η

π

8

---

39.25 %

==

To t a lP

diss

2P

diss1

2P

diss2

==

Tot a lP

di ss

22 V

CC

π R

L

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

OUT

2P

OUT

–

=

Tot a lP

di ss

42 V

CC

π R

L

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

OUT

2P

OUT

–

=