AN160| Application Note
Application Note 160
Using the DS1808 in Audio Applications
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Introduction
The DS1808 Dual Log Audio Potentiometer was designed to provide superior audio performance in applications that require low levels of THD and cross-talk. By utilizing a 12V supply, it offers 24Vpp of signal swing capability, and it simplifies your design by allowing the low side of the potentiometer to be referenced to ground. The DS1808 features 33 positions that provide attenuation from 0dB to 60dB, and a mute function that provides 90dB of attenuation. It is controlled by a 2-wire interface, which can address up to eight DS1808s on a single 2-wire bus. It is available in a 16-pin SOIC package. This application note addresses both hardware and software design practices that will allow the DS1808 to work best in a customer's application. When the DS1808 is used according to these practices it is a viable solution for most audio applications.
Basic Audio Circuit Using a Dual Supply Digital Potentiometer
There are several circuit topologies that can be used to create an audio circuit with a digital potentiometer utilizing a 12V supply. Dual supply digital potentiometers can directly replace a mechanical potentiometer in most instances as long as the full range of the signal is within the supply range of the potentiometer, and the output current required at the wiper does not exceed the wiper current specification. A simple audio circuit using the DS1808 is shown in Figure 1.
Figure 1
A Basic Audio Circuit that Could be Built Using the DS1808. This circuit will work using a DS1808 as long as the input voltages are less than VCC and greater than Vb. The input is AC coupled from the audio source, and the output has a capacitor in series to guarantee that the output will also be AC coupled. Once the audio signal has made it past the input capacitor, it will be attenuated by the DS1808 according to how its registers have been set with the 2-wire bus. The DS1808 has a graduated logarithmic taper with 1dB steps from 0 to 12dB, 2dB steps from 14dB to 36dB, and 3dB steps from 39dB to 60dB. The last register position is mute, which provides greater than 90dB attenuation. The wiper output of the potentiometer will be amplified by a fixed gain of 7.8V/V (17.8dB) by the operational amplifier. The amplifier serves as a voltage buffer, which by design keeps the wiper current of the DS1808 below the specified value of 1mA with its high impedance input.
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