Elektronische Bauelemente

01-Jun-2002 Rev. A

Page 4 of 9

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Any changing of specification will not be informed individual

Design Guidelines

General

The

low voltages. The differential gain is set by two external resistors. Pins FC1 and FC2 allow controlling the amount of power supply and

noise rejection, as well as providing alternate inputs to the amplifiers. The CD pin permits powering down the IC for muting purposes and

to conserve power.

Amplifiers

Referring to the block diagram, the internal configuration consists of two identical operational amplifiers. Amplifier # 1 has an open loop

gain of

80 dB (at f

unity gain frequency of approximately 1.5 MHz. In order to adequately cover the telephone voice band (300 Hz to 3400 Hz), a maximum

closed loop gain of 46 is recommended. Amplifier #2 is internally set to a gain of-1.0(0dB).

The outputs of both amplifiers are capable of sourcing and sinking a peak current of 200 mA. The outputs can typically swing to within

offset voltages. The input offset voltage of the two amplifiers swill generally be similar for a particular IC, and therefore nearly cancel each

measured with the feedback resistor shown in the Typical Application Circuit, and therefore takes into account the bias current as well as

FC1 and FC2

Power supply rejection is provided by the capacitors (C1 and C2 in the Typical Application Circuit) at FC1 and FC2. C2 is somewhat

dominant at low frequencies, while C1 is dominant at high frequencies, as shown in the graphs of Figures 4 to 7. The required values of

C1 and C2 depend on the conditions of each application. A line powered speakerphone, for example, will require more filtering than a

circuit powered by a well regulated power supply. The amount of rejection is a function of the capacitors, and the equivalent impedance

In addition to providing filtering, C1 and C2 also affect the turn-on time of the circuit at power-up, since the two capacitors must charge

SPW34119D

Low Power Audio

Amplifier