Datasheet
LM4811
SNAS119D –DECEMBER 2000–REVISED APRIL 2013
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APPLICATION INFORMATION
DIGITAL VOLUME CONTROL
The LM4811's gain is controlled by the signals applied to the CLOCK and UP/DN inputs. An external clock is
required to drive the CLOCK pin. At each rising edge of the clock signal, the gain will either increase or decrease
by a 3dB step depending on the logic voltage level applied to the UP/DN pin. A logic high voltage level applied to
the UP/DN pin causes the gain to increase by 3dB at each rising edge of the clock signal. Conversely, a logic
low voltage level applied to the UP/DN pin causes the gain to decrease 3dB at each rising edge of the clock
signal. For both the CLOCK and UP/DN inputs, the trigger point is 1.4V minimum for a logic high level, and 0.4V
maximum for a logic low level.
There are 16 discrete gain settings ranging from +12dB maximum to −33dB minimum. Upon device power on,
the amplifier's gain is set to a default value of 0dB. However, when coming out of shutdown mode, the LM4811
will revert back to its previous gain setting.
The LM4811's CLOCK and UP/DN pins should be debounced in order to avoid unwanted state changes during
transitions between V
IL
and V
IH
. This will ensure correct operation of the digital volume control. A microcontroller
or microprocessor output is recommended to drive the CLOCK and UP/DN pins.
Figure 41. Timing Diagram
POWER DISSIPATION
Power dissipation is a major concern when using any power amplifier and must be thoroughly understood to
ensure a successful design. Equation 1 states the maximum power dissipation point for a single-ended amplifier
operating at a given supply voltage and driving a specified output load.
P
DMAX
= (V
DD
)
2
/ (2π
2
R
L
) (1)
Since the LM4811 has two operational amplifiers in one package, the maximum internal power dissipation point
is twice that of the number which results from Equation 1. Even with the large internal power dissipation, the
LM4811 does not require heat sinking over a large range of ambient temperature. From Equation 1, assuming a
5V power supply and a 32Ω load, the maximum power dissipation point is 40mW per amplifier. Thus the
maximum package dissipation point is 80mW. The maximum power dissipation point obtained must not be
greater than the power dissipation predicted by Equation 2:
P
DMAX
= (T
JMAX
− T
A
) / θ
JA
(2)
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