sx8675iwltrt Semtech Corporation, sx8675iwltrt Datasheet - Page 27

• Manufacturer Part Number: sx8675iwltrt
• Description: Haptics Enabled Multitouch 4/5-wire Resistive Touchscreen Controller With Proximity Sensing
• Manufacturer: Semtech Corporation

ADVANCED COMMUNICATIONS & SENSING
5.2.3
PROXSENSORCON defines which pin will act as the sensor during proximity sensing operations. In the typical
case, the touchscreen top layer is used as the sensor (exact pin/electrode depends on screen type/structure).
Else, the sensor can also be “external”, i.e. connected to AUX2.
The sensitivity of the interface is defined by PROXSENSITIVITY; for obvious power consumption reasons it is
recommended to set it as low as possible.
As a last resort and only if the sensor is “external”, PROXBOOST can be set to allow higher sensitivity if needed.
PROXFREQ defines the operating frequency of the interface and should be set as high as possible for power
consumption reasons.
If needed, PROXHIGHIM enables a high noise immunity mode at the expense of increased power consumption.
5.2.4
PROXSHIELDCON defines which pin will act as the shield during proximity sensing operations. In the typical
case, the shield will usually be the touchscreen bottom layer (exact pin/electrode depends on screen
type/structure). Else, the shield can also be “external”, ie a simple copper area on the PCB connected to AUX3.
5.2.5
Offset compensation consists in performing a one time measurement of C
capacitance C
The ADC input C
There are five possible compensation sources which are illustrated in the figure below. When set to 1 by any of
these sources, PROXCOMPSTAT will only be reset once the compensation is completed.
Rev 1 – 25
Capacitance-to-Voltage Conversion (C-to-V)
Shield Control
Offset Compensation
th
July 2011
Sensor
User
in order to feed the ADC with the closest contribution of C
is the total capacitance C
Figure 32 – Offset Compensation Block Diagram
Figure 33 – Compensation Request Sources
Sensor
Resistive Touchscreen Controller with Proximity Sensing
to which C
27
Env
is subtracted.
SX8674/SX8675/SX8676
Haptics Enabled Multitouch 4/5-Wire
User
Env
only.
and subtracting it to the total
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