POUT= VPEAK22RLW

(6)

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

IccAVG=2VPEAKπRLA

(7)

The power delivered by the supply voltage is Psupply = Vcc IccAVG (W)

Then, the power dissipated by the amplifier is Pdiss = Psupply - Pout (W)

Pdiss= 2 2VccπRL POUT−POUTW

(8)

and the maximum value is obtained when:

∂Pdiss

∂POUT=0

(9)

and its value is:

Pdissmax = 2VCC2π2RLW

(10)

Remark : This maximum value is only depending on power supply voltage and load values.

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

η= POUTPsupply=πVPEAK4VCC

(11)

The maximum theoretical value is reached when

Vpeak = Vcc, so

π4=78.5%

(12)

5.5

Decoupling of the circuit

Two capacitors are needed to bypass properly the TS419/TS421. 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 1 μF, you can expect similar THD+N performances 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.

TS419, TS421

Application information

DS3048 - Rev 7

page 30/42