5.3

Low and high frequency response

In low frequency region, the effect of Cin starts. Cin with Rin forms a high pass filter with a -3 dB cut-off frequency

FCL= 12πRinCinHz

In high frequency region, you can limit the bandwidth by adding a capacitor (Cfeed) in parallel on Rfeed. Its form a

low pass filter with a -3 dB cut-off frequency.FCH= 1

2πRfeedCfeed Hz

5.4

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=VPEAKsinωtt

and

IOUT= VOUTRLA

POUT= VPEAK22RLW

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

IccAVG=2VPEAKπRLA

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

and the maximum value is obtained when:

∂Pdiss

∂POUT=0

and its value is:

Pdissmax = 2VCC2π2RLW

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

The maximum theoretical value is reached when

Vpeak = Vcc, so

π4=78.5%

TS4871

Application information

DS2547 - Rev 10

page 25/42