LM4832 datasheet(15/22 Pages) NSC

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Application Information (Continued)

GENERAL PURPOSE OUTPUT PIN

The General Purpose Output pin is intended to be used as a

control signal for other devices, such as an external power

amplifier. This pin is controlled through the I

2C interface and

is not relatedto any other functions within the LM4832. Refer

to the Truth Tables section for the proper I

2C data bits to uti-

lize this function.

Figure 7 shows an example of using the General Purpose

Output to interface with an external power amp. In this case,

the external power amp is the LM4755 stereo 10 watt per

channel (rms) power amplifier with mute. AC-coupling ca-

pacitors must be used to remove the DC bias present be-

tween the LM4832 outputs and the external power amplifier

inputs.

Prior to placing any of the preamp circuitry in shutdown, the

General Purpose Output should be used to disable the exter-

nal power amplifier.This will prevent any shutdown transients

in the preamp circuitry from being amplified by the external

power amplifier.

LOOP IN/OUT PINS

The Loop In and Loop Out pins are used when an application

requires a special function to be performed on the audio sig-

nal. As shown in

Figure 7, the audio signal is taken from the

Loop Out pin and sent to an external signal processor. After

the signal is processed externally, it is fed back into the Loop

In pin.

An example of where this functionality would be used is com-

puter speakers. The external loop could be used to provide

bass boost to counteract the speaker’s natural or baffle-

induced rolloff.

Since the Loop In pin goes directly to the input of a CMOS

amplifier, the input impedance is very high. The Loop Out pin

is driven by the input attenuation amplifier, which is capable

of driving impedances as low as 1 k

Ω.

DS100014-29

FIGURE 6. Tone Control Diagram

DS100014-30

10W/ch System with I

2C Controlled Tone,Volume and 3D Sound

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