AD7143ACPZ Analog Devices Inc, AD7143ACPZ Datasheet - Page 25

• Manufacturer Part Number: AD7143ACPZ
• Description: IC, CDC, 16BIT, SMD, LFCSP-16, 7143
• Manufacturer: Analog Devices Inc

Specifications of AD7143ACPZ

• Supply Voltage Range: 2.6V To 3.6V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: LFCSP
• No. Of Pins: 16
• Svhc: No SVHC (18-Jun-2010)
• Package / Case: LFCSP
• Base Number: 7143
• Ic Function: Programmable Controller For Capacitance Touch Sensors
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADAPTIVE THRESHOLD AND SENSITIVITY
The AD7143 provides an on-chip self-learning adaptive
threshold and sensitivity algorithm. This algorithm continu-
ously monitors the output levels of each sensor and automatically
rescales the threshold levels proportionally to the sensor area
covered by the user. As a result, the AD7143 maintains optimal
threshold and sensitivity levels for all types of users regardless
of their finger sizes.
The threshold level is always referenced from the ambient level
and is defined as the CDC converter output level that must be
exceeded for a valid sensor contact. The sensitivity level is
defined as how sensitive the sensor is before a valid contact is
registered.
Figure 36 provides an example of how the adaptive threshold and
sensitivity algorithm works. The positive and negative sensor
threshold levels are calculated as a percentage of the
STAGE_OFFSET_HIGH and STAGE_OFFSET_LOW values
based on the threshold sensitivity settings and the ambient value.
STAGE_OFFSET_HIGH
STAGE_OFFSET_LOW
THRESHOLD LEVEL
AMBIENT LEVEL
62.51% = POS
NEG ADAPTIVE THRESHOLD LEVEL = 39.08%
ADAPTIVE
Figure 36. Threshold Sensitivity Example with POS_THRESHOLD_SENSITIVITY = 1000 and NEG_THRESHOLD_SENSITIVITY = 0011
95.32%
25%
B
A
SENSOR CONTACTED
BY SMALL FINGER
AVERAGE MAX VALUE
95.32%
25%
STAGE_OFFSET_HIGH
IS UPDATED HERE
Rev. 0 | Page 25 of 56
62.51% = POS ADAPTIVE
THRESHOLD LEVEL
NEG ADAPTIVE THRESHOLD LEVEL = 39.08%
STAGE_OFFSET_LOW
IS UPDATED HERE
On configuration, initial estimates are supplied for both
STAGE_OFFSET_HIGH and STAGE_OFFSET_LOW after
which the calibration engine automatically adjusts the
STAGE_HIGH_THRESHOLD and STAGE_LOW_THRESHOLD
values for sensor response.
Reference A in Figure 36 shows an under sensitive threshold
level for a small finger user, demonstrating the disadvantages of
a fixed threshold level. By enabling the adaptive threshold and
sensitivity algorithm, the positive and negative threshold levels
are determined by the POS_THRESHOLD_SENSITIVITY and
NEG_THRESHOLD_SENSITIVITY register values and the
most recent average maximum sensor output value. These
registers can be used to select 16 different positive and negative
sensitivity levels ranging between 25% and 95.32% of the most
recent average maximum output level referenced from the
ambient value. The smaller the sensitivity percentage setting,
the easier it is to trigger a sensor activation. Reference B shows
that the positive adaptive threshold level is set at almost mid-
sensitivity with a 62.51% threshold level by setting
POS_THRESHOLD_SENSITIVITY = 1000. Figure 36 also
provides a similar example for the negative threshold level with
NEG_THRESHOLD_SENSITIVITY = 0001.
95.32%
AVERAGE MAX VALUE
25%
SENSOR CONTACTED
95.32%
BY LARGE FINGER
25%
STAGE_OFFSET_HIGH
IS UPDATED
STAGE_OFFSET_LOW
IS UPDATED HERE
AD7143