8002

8002

8002

8002

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Power Amplifier Design, for a more complete explanation of proper gain selection. Besides gain, one of the major

considerations is the closedloop bandwidth of the amplifier. To a large extent, the bandwidth is dictated by the choice of

external components shown in Figure 1. The input coupling capacitor, Ci, forms a first order high pass filter which

limits low frequency response. This value should be chosen based on needed frequency response for a few distinct

reasons.

Selection of Input Capacitor Size

Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certain sized capacitor is

needed to couple in low frequencies without severe attenuation. But in many cases the speakers used in portable

systems, whether internal or external, have little ability to reproduce signals below 100Hz to 150Hz. Thus, using a large

input capacitor may not increase actual system performance.

In addition to system cost and size, click and pop performance is effected by the size of the input coupling capacitor, Ci.

A larger input coupling capacitor requires more charge to reach its quiescent DC voltage (nominally 1/2 VDD). This

charge comes from the output via the feedback and is apt to create pops upon device enable. Thus, by minimizing the

capacitor size based on necessary low frequency response, turn-on pops can be minimized.

Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value. Bypass

capacitor, CB, is the most critical component to minimize turn-on pops since it determines how fast the 8002 turns on.

The slower the 8002’s outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the smaller the turn-on pop.

Choosing CB equal to 1.0µF along with a small value of Ci (in the range of 0.1µF to 0.39µF), should produce a

virtually clickless and popless shutdown function. While the device will function properly, (no oscillations or

motorboating), with CB equal to 0.1µF, the device will be much more susceptible to turn-on clicks and pops. Thus, a

value of CB equal to 1.0µF is recommended in all but the most cost sensitive designs.

AUDIO POWER AMPLIFIER DESIGN

A 1W/8

Audio Amplifier

Given:

Power Output

Load Impedance

Input Level

Input Impedance

Bandwidth

A designer must first determine the minimum supply rail to obtain the specified output power. By extrapolating from

the Output Power vs Supply Voltage graphs in the Typical Performance Characteristics section, the supply rail can be

easily found.

5V is a standard voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom

that allows the 8002 to reproduce peaks in excess of 1W without producing audible distortion. At this time, the designer

must make sure that the power supply choice along with the output impedance does not violate the conditions explained

in the Power Dissipation section.

1Wrms

8

1Vrms

20k

100Hz–20kHz ± 0.25dB