TS4990IST datasheet(20/33 Pages) STMICROELECTRONICS

20 / 33 page

Application information

TS4990

20/33

DocID9309 Rev 14

Therefore, 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:

4.5

Decoupling of the circuit

Two capacitors are needed to correctly bypass the TS4990: a power supply bypass

capacitor Cs and a bias voltage bypass capacitor Cb.

Cs has particular influence on the THD+N in the high frequency region (above 7 kHz) and an

indirect influence on power supply disturbances. With a value for Cs of 1 µF, you can expect

THD+N levels similar to those shown in the datasheet.

In the high frequency region, if Cs is lower than 1 µF, it increases THD+N and disturbances

on the power supply rail are less filtered.

On the other hand, if Cs is higher than 1 µF, those disturbances on the power supply rail are

more filtered.

Cb 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).

If Cb is lower than 1 µF, THD+N increases at lower frequencies and PSRR worsens.

If Cb is higher than 1 µF, the benefit on THD+N at lower frequencies is small, but the benefit

to PSRR is substantial.

Note that Cin has a non-negligible effect on PSRR at lower frequencies. The lower the value

of Cin, the higher the PSRR.

diss

22V

 R

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

out Pout

–

P

diss

P

out

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

diss

max



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

(W)

 =

out

supply

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

V

PEAK

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



----- = 78.5%

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