TS4890 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

TS4890

RAIL TO RAIL OUTPUT 1W AUDIO POWER AMPLIFIER WITH STANDBY MODE ACTIVE LOW

STMicroelectronics 

TS4890

s Power dissipation and efficiency

Hypothesis :

• Voltage and current in the load are sinusoidal

(Vout and Iout)

• Supply voltage is a pure DC source (Vcc)

Regarding the load we have :

VOUT = VPEAK sinωt (V)

and

IOUT

=

VOUT

RL

(A)

and

POUT =

VPEAK 2

2RL

(W)

Then, the average current delivered by the supply

voltage is

IccAVG

=

2

VPEAK

π RL

(A)

The power delivered by the supply voltage is

Psupply = Vcc IccAVG (W)

Then, the power dissipated by the amplifier is

Pdiss = Psupply - Pout (W)

2 2 Vcc

Pdiss =

POUT − POUT (W)

π RL

and the maximum value is obtained when

∂Pdiss = 0

∂POUT

and its value is

Pdiss max

=

2 Vcc2

π2RL

(W)

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 = POUT = π VPEAK

P supply 4 Vcc

The maximum theoretical value is reached when

Vpeak = Vcc, so

π = 78.5%

4

s Decoupling of the circuit

Two capacitors are needed to bypass properly the

TS4890. A power supply bypass capacitor Cs and

a bias voltage bypass capacitor Cb.

Cs has especially an influence on the THD+N in

high frequency (above 7kHz) and indirectly on the

power supply disturbances.

With 100µF, you can expect similar THD+N

performances like shown in the datasheet.

If Cs is lower than 100µF, in high frequency

increase THD+N and disturbances on the power

supply rail are less filtered.

To the contrary, if Cs is higher than 100µF, those

disturbances on the power supply rail are more

filtered.

Cb has an influence on THD+N in lower frequency,

but its function is critical on the final result of PSRR

with input grounded in lower frequency.

If Cb is lower than 1µF, THD+N increase in lower

frequency (see THD+N vs frequency curves) and

the PSRR worsens up

If Cb is higher than 1µF, the benefit on THD+N in

lower frequency is small but the benefit on PSRR

is substantial (see PSRR vs. Cb curves).

Note that Cin has a non-negligible effect on PSRR

in lower frequency. Lower is its value, higher is the

PSRR (see fig. 13).

s Pop and Click performance

In order to have the best performances with the

pop and click circuitry, the formula below must be

follow :

τin ≤ τb

With

τin = (Rin + Rfeed ) × Cin (s)

and

τb = 50kΩ × Cb (s)

25/32

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