MAX11800_1010 Datasheet, PDF (19/59 Pages) Maxim Integrated Products – Low-Power, Ultra-Small Resistive Touch-Screen Controllers with I2C/SPI Interface

Low-Power, Ultra-Small Resistive Touch-Screen
Controllers with I²C/SPI Interface
Table 2. Operating Modes, Conditions, and Options
OPERATION _{PSU PMC CMC TDM LPM AVG FIFO APER} PUR _{CONT MTAG ETAG} X, Y, _{EINT CINT} COR
MODE
PUF
Z1, Z2
INT
DCM
MAX11800– Yes Yes Yes Yes No Yes No
MAX11803
No Yes Yes Yes ² Yes ² Yes Yes Yes No
ACM
MAX11800/ Yes ¹ Yes ¹ Yes ¹ Yes Yes Yes Yes Yes Yes No Yes Yes Yes No No Yes
MAX11801
AUX
No Yes ³ No No — Yes ³ No No No No
No
No
No No No No
1_{In ACM, the choices are limited to X and Y scan, or X and Y and Z1 scan, or X and Y and Z1 and Z2 scan.}
2_{In DCM, MTAG is always used. For DCM with CONT = 0, the following ETAGs are used: 00 = touch present (data valid), 10 = no}
touch present (data may be invalid), 11 = measurement in progress (data invalid). For DCM with CONT = 1, the panel cannot be
scanned for a touch because panel setup switches are configured in a measurement mode; therefore, ETAG = 00 is used if a mea-
surement is not in progress, or ETAG = 11 if a measurement is in progress.
3_{A separate configuration register for delay time, sampling time, averaging, and ADC resolution settings configures the AUX input.}
Pressure Measurements
Z1 and Z2 measurements determine the resistance
between the two planes within the panel sensor during
a touch (R_TOUCH). Depending on the known physical
properties of the panel, one of two equations extract the
value of R_TOUCH, providing information about the pres-
sure and area of the touch applied to the panel. Allow
adequate time for the panel to settle when switching
between position and pressure measurements. Figure 5
shows the physical setup of the panel when performing
pressure measurements.
Z1 and Z2 measurements allow observation of the volt-
age on either side of the effective R_TOUCH resistance.
With both Z1 and Z2 measurements available, compute
R_TOUCH as follows:
R_TOUCH
=
R_XPLATE
⎛
⎝⎜
X_POSITION
2^NBITX
⎞
⎠⎟
⎛
⎝⎜
Z₂
Z₁
−1^{⎞⎠⎟}
If only a Z1 measurement is available, compute
R_TOUCH as follows:
R_TOUCH
=
⎛
⎝⎜
R_XPLA2TENBX_IPTOXSITION ⎞⎠⎟
⎛
⎝⎜
2^NBITZ
Z₁
− 1^{⎞⎠⎟}
−
R_YPLATE
⎛⎝⎜_1−
Y_POSITION
2^NBITY
⎞
⎠⎟
The power applied across the panel during pressure
measurements is greatly dependent on R_TOUCH and
the physical position of the touch. The maximum power
dissipation in the panel during a pressure measurement
is approximately P_Z = V_DD²/R_TOUCH. This maximum
PANEL
RTOUCH
ADC
Y+ ^INPUT
PANEL
RTOUCH
Y+ VDD
PANEL
RTOUCH
Y+ VDD
PANEL
RTOUCH
Y+ VDD
Y-
X-
X+
VDD
X POSITION MEASUREMENT
Y-
X-
X+
ADC
INPUT
Y POSITION MEASUREMENT
Y-
X-
X+
ADC
INPUT
Z1 PRESSURE MEASUREMENT
ADC
Y- ^INPUT
X-
X+
Z2 PRESSURE MEASUREMENT
Figure 4. Position Measurements
Figure 5. Pressure Measurements
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