MXT1664T3-ABESSQTP datasheet(29/98 Pages) MICROCHIP

29 / 98 page

MXT1664T3 2.0

 2018 Microchip Technology Inc.

DS40002054A-page 29

6.0

DETAILED OPERATION

6.1

Touch Detection

The mXT1664T3 allows for both mutual and self capacitance measurements, with the self capacitance measurements

being used to augment the mutual capacitance measurements to produce reliable touch information.

When self capacitance measurements are enabled, touch classification is achieved using both mutual and self

capacitance touch data. This has the advantage that both types of measurement systems can work together to detect

touches under a wide variety of circumstances.

Mutual capacitance touch data is used wherever possible to classify touches as this has greater granularity than self

capacitance measurements and provides positional information on touches.

Self capacitance measurements, on the other hand, allow for the detection of single touches in extreme cases, such as

single thick glove touches, when touches can only be detected by self capacitance data and may be missed by mutual

capacitance touch detection.

6.2

Operational Modes

The device operates in two modes: Active (touch detected) and Idle (no touches detected). Both modes operate as a

series of burst cycles. Each cycle consists of a short burst (during which measurements are taken) followed by an

inactive sleep period. The difference between these modes is the length of the cycles. Those in idle mode typically have

longer sleep periods. The cycle length is configured using the IDLEACQINT and ACTVACQINT settings in the Power

Configuration T7. In addition, an Active to Idle Timeout setting is provided.

6.3

Detection Integrator

The device features a touch detection integration mechanism. This acts to confirm a detection in a robust fashion. A

counter is incremented each time a touch has exceeded its threshold and has remained above the threshold for the

current acquisition. When this counter reaches a preset limit the sensor is finally declared to be touched. If, on any

acquisition, the signal is not seen to exceed the threshold level, the counter is cleared and the process has to start from

the beginning.

The detection integrator is configured using the appropriate touch objects (Multiple Touch Touchscreen T100).

6.4

Sensor Acquisition

The charge time is set using the Acquisition Configuration T8 object.

A number of factors influence the acquisition time for a single drive line and the total acquisition time for the sensor as

a whole must not exceed 250 ms. If this condition is not met, a SIGERR will be reported.

Care should be taken to configure all the objects that can affect the measurement timing, for example, Acquisition

Configuration T8, CTE Configuration T46 and Self Capacitance Configuration T111, so that these limits are not

exceeded.

6.5

Calibration

Calibration is the process by which a sensor chip assesses the background capacitance on each node. Nodes are only

calibrated on reset and when:

• The node is enabled (that is, activated)

• The node is already enabled and one of the following applies:

- The node is held in detect for longer than the Touch Automatic Calibration setting (TCHAUTOCAL in the

Acquisition Configuration T8 object)

- The signal delta on a node is at least the touch threshold (TCHTHR – TCHHYST) in the anti-touch direction,

while it meets the criteria in the Touch Recovery Processes that results in a recalibration

- The host issues a recalibrate command

- Certain configuration settings are changed

A status message is generated on the start and completion of a calibration.

Note that the device performs a global calibration; that is, all the nodes are calibrated together.

MXT1664T3-ABESSQTP Datasheet(PDF) 29 Page - Microchip Technology

MXT1664T3-ABESSQTP Datasheet(HTML) 29 Page - Microchip Technology

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 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98

Datasheet Download

Link URL