2.375V to 5.25V, 4-Wire Touch-Screen Controller

with Internal Reference and Temperature Sensor

______________________________________________________________________________________

13

The first method performs pressure measurements

using a known X-plate resistance. After completing

three conversions (X-position, Z1, and Z2), use the fol-

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.

Internal Temperature Sensor

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-

is a well-defined characteristic. The ambient tempera-

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

R

Z

X

Z

R

Y

TOUCH

XPLATE

POSITION

YPLATE

POSITION

=











 ×











 ×





























×

























−

−

11

4096

4096

1

4096

RR

XZ

Z

TOUCH

XPLATE

POSITION

=











 ×





























−

4096

1

2

1

OPEN CIRCUIT

SENSE LINE

MEASURE Z2

MEASURE Z1

X+

X-

Y+

+

-

Y-

OPEN CIRCUIT

X+

X-

Y+

Y-

MEASURE X- POSITION

X- POSITION

OPEN CIRCUIT

X+

X-

Y+

Y-

V

+

-

V

+

-

V

Figure 7. Pressure Measurement Block Diagram

NO RESPONSE TO TOUCHMASK PENIRQ

PENIRQ ENABLED

SCREEN TOUCHED HERE

INTERRUPT PROCESSOR

SA2

A1

A0

M

S/D

PD1

PD0

12

3

4

5

6

78

1

2

3

1213

141516

PENIRQ

CS

DIN

DCLK

Figure 6. PENIRQ Timing Diagram