SX8657IWLTRT Semtech, SX8657IWLTRT Datasheet - Page 26

• Manufacturer Part Number: SX8657IWLTRT
• Description: 58T7570
• Manufacturer: Semtech

Specifications of SX8657IWLTRT

• Controller Type: Resistive Touch Screen
• Ic Interface Type: I2C, Serial
• Supply Voltage Range: 2.3V To 3.6V
• Operating Temperature Range: -40°C To +85°C
• No. Of Pins: 20
• Resolution (bits): 12bit

ADVANCED COMMUNICATIONS & SENSING
Please note that the compensation request flag can be set anytime but the compensation itself is always done at
the beginning of a scan period to keep all parameters coherent (PROXRAW, PROXAVG, PROXDIFF), see
§ 5.3.2.
5.2.6
A 12-bit ADC is used to convert the capacitance information into a digital 12-bit word PROXRAW.
The ADC is shared with the touchscreen interface using time multiplexing (see § 5.4.2 for more details).
5.3
5.3.1
The main purpose of the digital processing block is to convert the raw capacitance information coming from the
AFE (PROXRAW) into a robust and reliable digital flag (PROXSTAT) indicating if the user’s finger/hand/head is
close to the proximity sensor.
The offset compensation performed in the AFE is a one time measurement. However, the environment
capacitance C
estimation of C
by filtering PROXUSEFUL to extract its slow variations (PROXAVG).
PROXDIFF is then compared to user programmable threshold to extract PROXSTAT flag.
Digital processing sequencing is illustrated in figure below. At every scan period wake-up (defined by
PROXSCANPERIOD), the block updates sequentially PROXRAW, PROXUSEFUL, PROXAVG, PROXDIFF and
PROXSTAT before going back to Idle mode.
Rev 1 – 25
Digital Processing
Block startup: a compensation is automatically requested when the proximity sensing is enabled via
PROXSCANPERIOD.
I2C: a compensation can be manually requested anytime by the host through I2C interface.
PROXAVG update: a compensation can be automatically requested if it is detected that C
beyond a set level since the last compensation.
PROXCOMPPRD: a compensation can be automatically requested at a predefined rate programmed by
the host.
PROXSTUCK: a compensation can be automatically requested if it is detected that the proximity “Close”
state is lasting abnormally long.
Analog-to-Digital Conversion (ADC)
Overview
th
July 2011
Env
User
may vary with time (temperature, nearby objects, etc). Hence, in order to get the best
(PROXDIFF) it is needed to dynamically track and subtract C
Figure 31 – Digital Processing Block Diagram
Resistive Touchscreen Controller with Proximity Sensing
26
Env
SX8657/SX8658
variations. This is performed
Haptics Enabled 4/5-Wire
www.semtech.com
Env
has drifted