LTC1199 LINER [Linear Technology], LTC1199 Datasheet - Page 25

• Manufacturer Part Number: LTC1199
• Description: 10-Bit, 500ksps ADCs in MSOP with Auto Shutdown
• Manufacturer: LINER [Linear Technology]

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
TYPICAL
TOUCH SENSE
CHIP SELECT
SERIAL CLK
DATA OUT
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
DATA IN
5V
X
Y
X
Y
+
–
–
+
A
100k
PPLICATI
R9
74HC14
R8
4.7k
1000pF
C6
Q3
2N2222A
O
U
4.7k
R6
S
4.7k
R10
R7
100k
R11
100k
Q4
2N2222A
Q2
2N2907
C5
1000pF
C7
1000pF
2N2907
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.
Q1
R12
100k
C4
1000pF
R6
4.7k
100k
R7
100
100
R1
R2
LTC1197/LTC1197L
LTC1199/LTC1199L
C1
1 F
C2
1 F
1
2
3
4
CS
CH0
CH1
GND
LTC1199
10 F
D
C3
CLK
V
OUT
D
CC
IN
+
8
7
6
5
10
R3
1197/99 F13
25