SX8652IWLTRT Semtech, SX8652IWLTRT Datasheet - Page 13

• 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

4.3. Pressure Measurement
The 4-wire touchscreen allows pressure measurement. The contact resistance between the two sheets are a function of
the pressure applied on the top sheet. Indeed, the a low pressure applied with the finger will create a small contact area.
With a greater pressure, the contact area will be bigger and the R
The R
The measurement setup given in Table 7 allows to find Z1 and Z2.
Arranging Z1 and Z2 with Rxtot and Rytot allows the
computation of R
An alternative calculation method is using Xpos and Ypos.
4.4. Pen Detection
The pen detection circuitry is used to detect a user action on the
touchscreen. The contact between the two layers generates an interrupt or
starts an acquisition sequence.
Doing a pen detection prior to conversion avoids feeding the host with
dummy data and saves power.
If the touchscreen is powered between X+ and Y- through a resistor R
no current will flow so long as pressure is not applied to the surface (see
Figure 10).
When a pressure is applied, a current path is created and brings X+ to the
level defined by the resistive divider determined by R
R1, R
R
can also improve the detection on panel with high resistance.
The pen detection will set the PENIRQ bit of the RegStat register. The PENIRQ bit will be cleared and the NIRQ will be de-
asserted as soon as the host reads the status register.
In PENDET mode, the pen detection will set NIRQ low.
Revision V1.7/October 2010
©2010 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
z1
PNDT
=
T
T
should be set to the greatest value of 200 kOhm for optimal detection (see Table 15). Increasing PowDly settings
and R4.
contact resistance is therefore an indication of the applied pressure. R
4095
-------------------------------- -
R1
T
.
+
R4
R4
+
R
Measurement
T
Z1
Z2
X
Y
z2
=
4095
Table 7. Measurement setup
Vref +
-------------------------------- -
R1
X+
Y+
X+
X+
R4
+
PNDT
15kV ESD Low Power 4-Wire / 5-Wire Resistive
R4
Page 13
+
Rt
and the sum of
+
R
R
R
T
T
Touchscreen Controller with SPI Interface
T
T
=
=
resistance smaller.
Vref-
X-
Y-
Y-
Y-
Rytot
Rytot Ypos
------------------------------ -
PNDT
4095
,
Figure 10. 4-wire pen detection circuitry
Ypos
----------- -
T
4095
Vref
is deducted from Z1 and Z2 measurement.
+
-
ADC +
Y+
X+
Y+
X-
4095
----------- - 1
z2
---- - 1
z1
Y+
z1
Y-
R3
R4
–
R
T
–
X-
R1
R2
R
X+
–
PNDT
Rxtot
Internal
logic
www.semtech.com
DATASHEET
SX8652
Sb
Rb
Q
Q
1
–
IRQ
Xpos
------------ -
4095