SX8652IWLTRT Semtech, SX8652IWLTRT Datasheet - Page 25

• Manufacturer Part Number: SX8652IWLTRT
• Description: IC TOUCH SCREEN CTRLR 14DFN
• Manufacturer: Semtech
• Type: Resistiver

Specifications of SX8652IWLTRT

• Touch Panel Interface: 4-Wire, 5-Wire
• Number Of Inputs/keys: 2 Key
• Resolution (bits): 12 b
• Data Interface: Serial, SPI™
• Data Rate/sampling Rate (sps, Bps): 74k
• Voltage Reference: Internal
• Voltage - Supply: 1.65 V ~ 3.7 V
• Current - Supply: 10mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 14-DFN
• Voltage Supply Source: Single Supply
• Sampling Rate (per Second): 74k
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: SX8652IWLTR

capacitance of the touchscreen. We can define tau as the RC time constant. POWDLY duration should be programmed to
10 tau to reach 12 bit accuracy.
Adding a capacitor from the touch screen drivers to ground is a solution to minimize external noise but it increases settling
time and consequently the power consumption.
10.3.2. SETDLY
A best method to filter noise is described in section [6] (Data processing). When filtering is enabled, the channel will be
biased initially during a time of POWDLY for the first conversion. The parameter SETDLY sets the settling time between the
subsequent conversions in a filter set. In most applications, SETDLY can be set to 0. In applications with a high tau and
where accuracy of 1LSB is required SETDLY should be increased.
10.4. AUX Input - 4-wire touchscreen only
The AUX input can be used to sample an analog signal in the range 0-VDD. For system supply by battery, the battery
voltage can be monitored for example. The conversion is done in sequence with the touchscreen acquisition therefore the
sample rate is defined with RegCtrl0 in AUTO mode.
The AUX pin can also triggered conversions. A rising edge, a falling edge or both applied on the AUX pin can trigger the
conversion. This is defined by AUXACQ in RegCtrl1.
This method can be used to sample touchscreen when there is noise-free periods.
10.5. Interrupt Generation
An interrupt (NIRQ=0) will be generated:
The NIRQ will be released and pulled high(NIRQ=1) by the external pull-up resistor:
An active NIRQ (low) needs to be cleared before any new conversions will occur.
10.6. Coordinate Throughput Rate
The coordinate throughput rate depends on the following factors:
The coordinate rate is the frequency to get the X, Y, Z1 and Z2 coordinate:
10.6.1. SPI Communication Time
The minimum time to read the channel data in PENTRIG mode is:
The highest throughput will be obtained with a SPI frequency of 5MHz when the host read the channel data as quickly as
possible after the NIRQ falling edge.
Revision V1.7/October 2010
©2010 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
During the power-up phase or after a reset
After completion of a conversion in MANUAL, PENTRIG or AUTO mode. CONVIRQ (bit [7] of RegStat) will be set at the
same time.
After a touch on the panel being detected in PENDET mode. PENIRQ (bit [6] of RegStat) will be set at the same time.
When the power-up phase is finished
When the host read all channels data that were previously converted by the SX8652 in MANUAL, PENTRIG or AUTO
mode. CONVIRQ will be cleared at the same time.
When the host read the status register in PENDET mode. PENIRQ, will be cleared at the same time.
The SPI communication time: T
The conversion time: T
conv
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15kV ESD Low Power 4-Wire / 5-Wire Resistive
Page 25
Touchscreen Controller with SPI Interface
T
com
=
CoordRate
8
+
16
=
N
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T
chan
com
+
1
T
conv
T
SPI
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