LM4950

SNAS174E – JULY 2003 – REVISED MAY 2013

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Figure 66. Piezo-electric Transducer Capacitance

≤ 200nF

AUDIO POWER AMPLIFIER DESIGN

Audio Amplifier Design: Driving 4W into an 8

Ω BTL

The following are the desired operational parameters:

Power Output

4WRMS

Load Impedance

8

Ω

Input Level

0.3VRMS (max)

Input Impedance

20k

Ω

Bandwidth

50Hz–20kHz ± 0.25dB

The design begins by specifying the minimum supply voltage necessary to obtain the specified output power.

One way to find the minimum supply voltage is to use the Output Power vs Power Supply Voltage curve in

Typical Performance Characteristics section. Another way, using Equation 8, is to calculate the peak output

voltage necessary to achieve the desired output power for a given load impedance. To account for the amplifier's

dropout voltage, two additional voltages, based on the Clipping Dropout Voltage vs Power Supply Voltage in

Typical Performance Characteristics, must be added to the result obtained by Equation 8. The result is

Equation 9.

(8)

VDD = VOUTPEAK + VODTOP + VODBOT

(9)

20

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