LTC1197 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1197' PDF : 28 Pages View PDF
LTC1197/LTC1197L
LTC1199/LTC1199L
TYPICAL APPLICATIO S
Resistive Touchscreen Interface
Figure 13 shows the LTC1199 in a 4-wire resistive touch-
screen application. Transistor pairs Q1-Q3, Q2-Q4 apply
5V and ground to the X axis and Y axis, respectively. The
LTC1199, with its 2-channel multiplexer, digitizes the
voltage generated by each axis and transmits the conver-
sion results to the system’s processor through a serial
interface. RC combinations R1C1, R2C2 and R3C3 form
lowpass filters that attenuate noise from possible sources
such as the processor clock, switching power supplies
and bus signals. The 74HC14 inverter is used to detect
screen contact both during a conversion sequence and to
trigger its start. Using the single channel LTC1197, 5-wire
resistive touchscreens are as easily accommodated.
5V
R6
R7
4.7k
100k Q2
2N2907
C5
1000pF
Y+
X–
R9
100k
C6
1000pF
R8
4.7k
Q3
2N2222A
R7
Q1
100k
2N2907
C4
R6
1000pF 4.7k
R1
C1
100Ω
1µF
Y–
X+
TOUCH SENSE
74HC14
R10
4.7k
Q4
2N2222A
R11
100k
C7
R12
1000pF 100k
R2
C2
100Ω
1µF
R3
10Ω
+
C3
10µF
LTC1199
1
CS
2
CH0
3
CH1
4
GND
8
VCC
7
CLK
6
DOUT
5
DIN
CHIP SELECT
SERIAL CLK
DATA IN
DATA OUT
1197/99 F13
Figure 13. The LTC1199 Digitizes Resistive Touchscreen X and Y Axis Voltages. The ADC’s Auto Shutdown Feature
Helps Maximize Battery Life in Portable Touchscreen Equipment
25
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