Cirrus Logic CDB5566 - Manual (Page 7)

CDB5566
DS806DB3 7
For detailed information on the LMP7732 precision industrial op-amps, please visit National Semiconduc-
tor’s website at
www.national.com .
The analog inputs are designed for connections to differential input signals. The usable input voltage
range is -4.096 V to +4.096 V. The theoretical input frequency range of the CS5566
is from DC to the
Nyquist frequency of 2.5 kHz. The analog input buffer amplifiers are configured for a cutoff frequency of
16.8 kHz to band-limit noise into the ADC. Changing the cutoff frequency will change the noise bandwidth
accordingly.
3.3.2 Multiplexer
Analog input channel selection is controlled through the multiplexer. The multiplexer is configured with a
pull-down resistor on the MUX control line to enable input channel labeled "INPUT A" by default. To select
channel B, apply 3.3 V to the multiplexer input control line (MUX).
Signal levels for controlling the multiplexer that selects between analog input channels A and B is shown
in Table 3.
During multiplexing, the maximum sample rate for each channel is half that of the ADC’s maximum sam-
ple rate. Additionally, the Nyquist frequency for each channel is half of the ADC’s Nyquist frequency.
3.3.3 ADC Reset
The CS5566 ADC makes use of an externally generated power-on reset. Therefore, after power is ap-
plied to the ADC, the reset pin must be driven low then released. Pressing the Reset button generates a
reset cycle. A reset cycle can be generated at any time during ADC operation. The ADC RST pin (active
low) is held inactive through a pull-up resistor.
3.3.4 Voltage Reference
The voltage reference IC provided generates a 4.096 V precision reference.
3.3.5 ADC Reference Frequency
The reference frequency for the CS5566 ADC is provided by a 8.000 MHz oscillator.
Table 3. Analog Input Channel Selection
Multiplexer
Control Input (MUX)
Input Channel
Enabled
0 V A
3.3 V B