EVAL-AD7156EBZ Analog Devices Inc, EVAL-AD7156EBZ Datasheet - Page 8

• Manufacturer Part Number: EVAL-AD7156EBZ
• Description: Evaluation Board I.c.
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7156EBZ

• Sensor Type: Touch, Capacitive
• Interface: I²C
• Voltage - Supply: 1.8 V ~ 3.6 V
• Embedded: No
• Utilized Ic / Part: AD7156
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sensitivity: -
• Sensing Range: -
• Lead Free Status / Rohs Status: Supplier Unconfirmed

EVAL-AD7156
CAPACITIVE INPUT SETTINGS
The
up independently via the I
settings are described in the following sections and are valid for
both channels.
Ch1, Ch2
The Ch1 and Ch2 boxes allow you to enable or disable the
capacitive input channels individually.
Cin Range
The Cin Range box allows you to select the following capacitive
input ranges for each channel: 4 pF, 2 pF, 1 pF, or 0.5 pF.
Hysteresis
The Hysteresis box allows you to enable or disable threshold
hysteresis when operating in adaptive mode. The hysteresis is
fixed to ±¼ of the threshold sensitivity and can be programmed
on or off.
Threshold Sensitivity
The Threshold Sensitivity box allows you to set a defined
sensitivity. This is defined as the distance between the data
average and the threshold in codes, as a fixed portion in the
range of the lower eight bits out of the 12-bit CDC full-scale
range of 0xA000 codes (d40944). Therefore, it represents a
different capacitive input value for each capacitive input range.
AD7156
DATA AVERAGE
THRESHOLD
POSITIVE
has two capacitive input channels that can be set
OUTPUT
Figure 18. AD7156 Capacitive Input Setup
Figure 19. Threshold Hysteresis
DATA
2
C-compatible interface. These AD7156
OUTPUT ACTIVE
TIME
HYSTERSIS
Rev. 0 | Page 8 of 16
Timeout Approaching, Timeout Receding
The Timeout Approaching box and Timeout Receding box
allow you to set a time after which the adaptive average and the
threshold adapt to a fast and seemingly permanent change in input
capacitance to ensure normal operation after the event.
INPUT CAPACITANCE
The number of conversion cycles, N
to elapse can be calculated using the following equation:
Average Time Constant
The Average Time Constant box allows you to determine how
fast the moving average adjusts to changes of the capacitive input
data. The adaptive threshold algorithm is based on an average
calculated from the previous CDC output data, using the following
equation:
CAPACITANCE
THRESHOLD
LARGE CHANGE
OUTPUT
N
Average
THRESHOLD
Figure 21. Approaching Timeout in Negative Threshold Mode
DATA AVERAGE
INPUT
C
OUTPUT ACTIVE
Figure 22. Receding Timeout in Negative Threshold Mode
DATA AVERAGE
THRESHOLD
THRESHOLD
OUTPUT
=
NEGATIVE
Roundup
POSITIVE
(
N
Shortens Period of Missing Output Trigger
)
=
Figure 20. Threshold Sensitivity
Shortens False Output Trigger
Average
OUTPUT ACTIVE
DATA
⎛
⎜
⎜
⎝
2
15
2
−
16
P
TIMEOUT RECEDING
TIMEOUT APPROACHING
+
(
−
1
N
1
−
−
1
) 1
⎞
⎟
⎟
⎠
+
with P value of register nibble
C
TIME
, required for the timeouts
Data
OUTPUT ACTIVE
(
N
2
)
ThrSettlin
−
SENSITIVITY
SENSITIVITY
Average
g
+
1
TIME
TIME
(
N
−
) 1