Application Information (Continued)
DS100014-29
FIGURE 6. Tone Control Diagram
GENERAL PURPOSE OUTPUT PIN
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.
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 I2C interface and
is not relatedto any other functions within the LM4832. Refer
to the Truth Tables section for the proper I2C data bits to uti-
lize this function.
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.
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
DS100014-30
10W/ch System with I2C Controlled Tone,Volume and 3D Sound
LOOP IN/OUT PINS
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 kΩ.
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.
15
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