LM4811 datasheet(11/18 Pages) NSC

11 / 18 page

Typical Performance Characteristics (Continued)

Power Supply Rejection Ratio

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Frequency Response

Supply Current vs

Supply Voltage

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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 de-

bounced in order to avoid unwanted state changes during

transitions between V

IL and VIH. 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.

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FIGURE 2. Timing Diagram

LM4811 Datasheet(PDF) 11 Page - National Semiconductor (TI)