Configuration Setting
ADC_SDOUT
(pin 13)
AIN5_MUX
(pin 1)
AIN5 Input Selection
Differential Input (pins 50 & 49)
AIN5A Input (pin 50)
47 kΩ Pull-down
47 kΩ Pull-up
47 kΩ Pull-up
X
Low
High
AIN5B Input (pin 49)
Table 3. AIN5 Analog Input Selection
Configuration Setting
ADC_SDOUT
(pin 13)
AIN6_MUX
(pin 2)
AIN6 Input Selection
Differential Input (pins 52 & 51)
AIN5A Input (pin 52)
47 kΩ Pull-down
47 kΩ Pull-up
47 kΩ Pull-up
X
Low
High
AIN5B Input (pin 51)
Table 4. AIN6 Analog Input Selection
Software Mode
Single-Ended mode is selected using the ADC3_SINGLE bit. Analog input selection is then
made via the AINx_MUX bits. See register “ADC Control & DAC De-emphasis (address 05h)”
on page 45 for all bit selections. Refer to Figure 10 on page 28 for the internal ADC3 analog input
topology.
5.2.3 High Pass Filter and DC Offset Calibration
The high pass filter continuously subtracts a measure of the DC offset from the output of the dec-
imation filter. If the high pass filter is disabled during normal operation, the current value of the
DC offset for the corresponding channel is frozen and this DC offset will continue to be subtract-
ed from the conversion result. This feature makes it possible to perform a system DC offset cal-
ibration by:
1) Running the CS42438 with the high pass filter enabled until the filter settles. See the Digital
Filter Characteristics for filter settling time.
2) Disabling the high pass filter and freezing the stored DC offset.
Hardware Mode
The high pass filters for ADC1 and ADC2 are permanently enabled in Hardware Mode. The high
pass filter for ADC3 is enabled by driving the ADC3_HPF (pin 4) high.
Software Mode
The high pass filter for ADC1/ADC2 can be enabled and disabled. The high pass filter for ADC3
can be independently enabled and disabled. The high pass filters are controlled using the
HPF_FREEZE bit in the register “ADC Control & DAC De-emphasis (address 05h)” on page 45.
DS646PP2
29
CIRRUS [ CIRRUS LOGIC ]
