CS4270_06 Datasheet, PDF (29/49 Pages) Cirrus Logic – 24-Bit, 192 kHz Stereo Audio CODEC

CS4270
Figure 17. A/D Dynamic Range vrs. Input Source Resistance
Attenuation: The required attenuation factor depends on the magnitude of the input signal. For
VA = 5 V, the full-scale input voltage equals 1 Vrms. The full-scale input voltage scales with VA as indi-
cated on pages 13 and 14. The user should select values for R1 and R2 such that the magnitude of the
incoming signal multiplied by the attenuation factor is less than or equal to the full-scale input voltage of
the device.
Input Impedance: Input impedance is the impedance from the signal source to the ADC analog input
pins. Table 6 shows the input parameters and the associated design equations.
Source Impedance
(_---R_----1----×_-----R_----2----)
R1 + R2
Attenuation Factor
(^---R^{----1(---R-+---2--}R^-)---2----)
Input Impedance
(R1 + R2)
Table 6. Analog Input Design Parameters
Figure 18 illustrates an example configuration using two 2 kΩ resistors in place of R1 and R2. This circuit
will attenuate a typical line level voltage, 2 Vrms, to the full-scale input of the ADC, 1 Vrms when VA = 5
V and is the maximum source impedance for the ADC specifications listed in this Data Sheet.
DS686PP1
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