ad7147a-1acbz-r Analog Devices, Inc., ad7147a-1acbz-r Datasheet - Page 17

• Manufacturer Part Number: ad7147a-1acbz-r
• Description: Captouch Programmable Controller For Single-electrode Capacitance Sensors
• Manufacturer: Analog Devices, Inc.

CAPACITANCE SENSOR INPUT CONFIGURATION
Each input connection from the external capacitance sensors to
the converter of the AD7147A can be uniquely configured by
using the stage configuration registers in Bank 2 (see Table 39).
These registers are used to configure the 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 differ-
ent sensitivity and offset values than a button with another
function that is connected to a different stage.
CINx INPUT MULTIPLEXER SETUP
Table 35 and Table 36 list the available options for the CINx_
CONNECTION_SETUP bits when the sensor input pins are
connected to the CDC.
The AD7147A has an on-chip multiplexer that routes the input
signals from each CINx pin to the input of the converter. Each
input pin can be tied to either the negative or positive input of
the CDC, or it can be left floating. Each input can also be
internally connected to the BIAS signal to help prevent cross-
coupling. If an input is not used, always connect it to BIAS.
Connecting a CINx input pin to the positive CDC input results
in an increase in CDC output code when the corresponding
sensor is activated. Connecting a CINx input pin to the negative
CDC input results in a decrease in CDC output code when the
corresponding sensor is activated.
The AD7147A performs a sequence of 12 conversions. The multi-
plexer can have different settings for each of the 12 conversions.
For example, CIN0 is connected to the negative CDC input for
conversion STAGE1, left floating for conversion STAGE1, and
so on, for all 12 conversion stages.
For each CINx input for each conversion stage, two bits control
how the input is connected to the converter, as shown in Figure 28.
Examples
To connect CIN3 to the positive CDC input on Stage 0, use the
following setting:
STAGE0_CONNECTION[6:0] = 0xFFBF
STAGE0_CONNECTION[12:7] = 0x2FFF
CIN10
CIN11
CIN12
CIN0
CIN1
CIN2
CIN3
CIN4
CIN5
CIN6
CIN7
CIN8
CIN9
CIN CONNECTION SETUP BITS
Figure 28. Input Mux Configuration Options
00
01
10
11
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CIN SETTING
CINx FLOATING
CINx CONNECTED TO
NEGATIVE CDC INPUT
CINx CONNECTED TO
POSITIVE CDC INPUT
CINx CONNECTED TO
BIAS
To connect CIN0 to the positive CDC input and CIN12 to the
negative CIN input on STAGE5, use the following settings:
STAGE5_CONNECTION[6:0] = 0xFFFE
STAGE5_CONNECTION[12:7] = 0x37FF
SINGLE-ENDED CONNECTIONS TO THE CDC
A single-ended connection to the CDC is defined as one CINx
input connected to either the positive or negative CDC input
for one conversion stage. A differential connection to the CDC is
defined as one CINx input connected to the positive CDC input
and a second CINx input connected to the negative input of the
CDC for one conversion stage.
For any stage, if a single-ended connection to the CDC is made
in that stage, the SE_CONNECTION_SETUP Bits[13:12] in the
STAGEx_CONNECTION[12:7] register should be applied as
described in Table 12.
Table 12. SE_CONNECTION_SETUP Bits
SE_CONNECTION_SETUP
00
01
10
11
The SE_CONNECTION_SETUP Bits[13:12] ensure that during a
single-ended connection to the CDC, the input paths to both
CDC terminals are matched, which, in turn, improves the
power-supply rejection of the converter measurement.
These bits should be applied in addition to setting the other bits
in the STAGEx_CONNECTION registers, as outlined in the
CINX Input Multiplexer Setup section.
If more than one CINx input is connected to either the positive
or negative input of the converter for the same conversion, set
SE_CONNECTION_SETUP to 11. For example, if CIN0 and
CIN3 are connected to the positive input of the CDC, set
SE_CONNECTION_SETUP to 11.
+
–
CDC
Description
Do not use.
Single-ended connection. For this
stage, there is one CINx connected
to the positive CDC input.
Single-ended connection. For this
stage, there is one CINx connected
to the negative CDC input.
Differential connection. For this
stage, there is one CINx connected
to the negative CDC input and one
CINx connected to the positive
CDC input.
AD7147A