mxb7846 Maxim Integrated Products, Inc., mxb7846 Datasheet - Page 13

• Manufacturer Part Number: mxb7846
• Description: Mxb7846 2.375v To 5.25v, 4-wire Touch-screen Controller With Internal Reference And Temperature Sensor
• Manufacturer: Maxim Integrated Products, Inc.

Figure 6. PENIRQ Timing Diagram
Figure 7. Pressure Measurement Block Diagram
with Internal Reference and Temperature Sensor
2.375V to 5.25V, 4-Wire Touch-Screen Controller
SCREEN TOUCHED HERE
MEASURE Z1
PENIRQ
CS
DCLK
DIN
+
-
V
OPEN CIRCUIT
t
TOUCH
X+
X-
X-
X-
X+
X+
______________________________________________________________________________________
R
R
X- POSITION
TOUCH
TOUCH
R
S
INTERRUPT PROCESSOR
TOUCH
1
OPEN CIRCUIT
OPEN CIRCUIT
A2
2
Y+
Y-
Y+
Y-
SENSE LINE
A1
Y+
Y-
3
A0
NO RESPONSE TO TOUCHMASK PENIRQ
MEASURE X- POSITION
4
V
V
+
-
+
-
M
5
MEASURE Z2
S/D
6
PD1
7
PD0
8
1
The first method performs pressure measurements
using a known X-plate resistance. After completing
three conversions (X-position, Z1, and Z2), use the fol-
lowing equation to calculate R
The second method requires knowing both the X-plate
and Y-plate resistance. Three conversions are required in
this method: the X-position, Y-position, and Z1-position.
Use the following equation to calculate R
The MXB7846 provides two temperature measurement
options: single-ended conversion and differential con-
version. Both temperature measurement techniques rely
on the semiconductor junction’s temperature character-
istics. The forward diode voltage (V
is a well-defined characteristic. The ambient tempera-
ture can be calculated by knowing the value of V
fixed temperature and then monitoring the change in
that voltage as the temperature changes. The single
conversion method requires calibration at a known tem-
perature, but only needs a single reading to calculate
the ambient temperature. First, the PENIRQ diode for-
R
2
TOUCH
R
TOUCH
3
−
=



R



 
=



YPLATE
R
(
12
R
XPLATE
XPLATE
Z
Internal Temperature Sensor
1
13
×

 ×




14
)
Y
×
POSITION
PENIRQ ENABLED



4096



15
X
X
POSITION
POSITION
TOUCH
4096
4096
16






BE
:
) vs. temperature

 ×


 ×

TOUCH:














4096
Z
Z
Z
2
1
1



BE
−



1
at a




−
13
1