AD7148 datasheet(16/56 Pages) AD

16 / 56 page

AD7148

Rev. 0 | Page 16 of 56

CAPACITANCE SENSOR INPUT CONFIGURATION

Each input connection from the external capacitance sensors to

the AD7148 converter can be uniquely configured by using the

registers in Bank 2 (see Table 39 through Table 42). 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 from those of a button with a different function that is

connected to a different stage.

CINx INPUT MULTIPLEXER SETUP

The CINx_CONNECTION_SETUP register bits provide options

for connecting the sensor input pins to the CDC (see Table 39

and Table 40).

The AD7148 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 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 corre-

sponding sensor is activated.

The AD7148 performs a sequence of eight conversions. The

multiplexer can have different connection settings for each of

the eight conversions by using the CINx_CONNECTION_

SETUP bits. For example, CIN0 can be connected to the

negative CDC input or left floating. The same holds true for all

eight conversion stages.

Two bits in each sequence stage register control the mux setting for

the input pin, as shown in Figure 25.

SINGLE-ENDED CONNECTIONS TO THE CDC

A single-ended connection to the CDC is defined as having one

CINx input connected to either the positive or the negative CDC

input. A differential connection to the CDC is defined as having

one CINx input connected to the positive CDC input and a second

CINx input connected to the negative input of the CDC.

When a single-ended connection to the CDC is made in any

stage, the SE_CONNECTION_SETUP bits in the STAGEx_

CONNECTION_SETUP registers should be applied. These bits

ensure that, during a single-ended connection to the CDC, the

input paths to both terminals are matched. This matching of

input paths, in turn, improves the power supply rejection of the

converter measurement.

Table 11. Application of SE_CONNECTION_SETUP Bits

Bit Values

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.

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 = 11. For example, if CIN0 and

CIN3 are connected to the positive input of the CDC,

SE_CONNECTION_SETUP = 11.

CIN0

CIN1

CIN2

CIN3

CIN4

CIN5

CIN6

CIN7

CIN SETTING

CINx_CONNECTION

_SETUP BITS

CINx FLOATING

CINx CONNECTED TO

NEGATIVE CDC INPUT

CINx CONNECTED TO

POSITIVE CDC INPUT

CINx CONNECTED TO

BIAS

CDC

–

Figure 25. Input Mux Configuration Options

AD7148 Datasheet(PDF) 16 Page - Analog Devices

AD7148 Datasheet(HTML) 16 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

Datasheet Download

Link URL