Datasheet

AD7142
Rev. A | Page 14 of 72
CAPACITANCE SENSOR INPUT CONFIGURATION
Each input connection from the external capacitance sensors to
the AD7142 converter can be uniquely configured by using the
registers in
Table 45 and Tabl e 46 . These registers are used to
configure input pin connection setups, sensor offsets, sensor
sensitivities, and sensor limits for each stage. Each sensor can be
individually optimized. For example, a button sensor connected
to STAGE0 can have different sensitivity and offset values than
a button with a different function that is connected to a
different stage.
CIN INPUT MULTIPLEXER SETUP
The CIN_CONNECTION_SETUP registers in Table 45 list the
different options that are provided for connecting the sensor
input pin to the CDC.
The AD7142 has an on-chip multiplexer to route the input
signals from each pin to the input of the converter. Each input
pin can be tied to either the negative or the positive input of the
CDC, or it can be left floating. Each input can also be internally
connected to the C
SHIELD
signal to help prevent cross coupling. If
an input is not used, always connect it to C
SHIELD.
Connecting a CINx input pin to the positive CDC input results
in a decrease in CDC output code when the corresponding
sensor is activated. Connecting a CINx input pin to the negative
CDC input results in an increase in CDC output code when the
corresponding sensor is activated.
The multiplexer settings for each conversion sequence can be
unique and different for each of the input pins, CIN0 to CIN13.
For example, CIN0 is connected to the negative CDC input for
conversion STAGE1, left floating for sequencer STAGE1, and so
on for all twelve conversion stages.
Two bits in each sequence stage register control the mux setting for
the input pin.
CIN0
CIN1
CIN2
CIN3
CIN4
CIN5
CIN6
CIN7
CIN8
CIN9
CIN10
CIN11
CIN SETTING
CIN_CONNECTION
_SETUP BITS
00
CINX FLOATING
01 CINX CONNECTED TO
NEGATIVE CDC INPUT
10
CINX CONNECTED TO
POSITIVE CDC INPUT
11
CINX CONNECTED TO
C
SHIELD
CDC
–
+
05702-010
CIN12
CIN13
Figure 21. Input Mux Configuration Options