fc = 1/(2πRLFE
C
)
LFE
Application Information (Continued)
The resulting low frequency differential gain of this bridged
amplifier becomes:
2(Rf + RLFE) / R = Avd
i
With RF = 20kΩ, RLFE = 20kΩ, and CLFE = 0.068 µF, a first
order pole is formed with a corner frequency of 120 Hz. At
low frequencies the differential gain will be 4, assuming RS
20kΩ. The low frequency boost formulas assume that CO
=
,
Ci, fIC, fOC allow the appropriate low frequency response.
The bass boost feature is enabled/disable by toggling the
logic at pin 3.
DC VOLUME CONTROL
The DC voltage at the DC Volume Control pin (pin 7) deter-
mines the attenuation of output of the amplifiers. If the DC
potential of pin 7 is at 4V (or 80% VDD) the internal amplifiers
are set at unity gain. The attenuator range is from 0dB (pin7
= 80% VDD) to -81dB (pin7 = 0V). Any DC voltage greater
than 4V (or 80% V DD) will result in a gain of unity. When the
mode pin is given a logic low,amplifiers will be fixed at a gain
of unity regardless of the voltage of pin 7. Refer to the Typi-
cal Performance Characteristics for detailed information of
the attenuation characteristics of the DC Volume Control pin.
DS100139-11
FIGURE 5. Low Frequency Enhancement
At low frequencies the capacitor will be virtually an open cir-
cuit. At high frequencies the capacitor will be virtually a short
circuit. As a result of this, the gain of the bridge amplifier is
increased at low frequencies. A first order pole is formed with
a corner frequency at:
13
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