MAX1233 Datasheet, PDF (16/44 Pages) Maxim Integrated Products – ±15kV ESD-Protected Touch-Screen Controllers Include DAC and Keypad Controller

±15kV ESD-Protected Touch-Screen
Controllers Include DAC and Keypad Controller
V_REF
SW1
SW2
SW255
TOUCH
OUT
SCREEN
+AV_DD
1MΩ
S1
TOUCH-SCREEN
DETECTOR
PENIRQ
X+
Figure 5. DAC Current-Steering Topology
Output Buffer
The DAC voltage output is an internally buffered unity-
gain follower that slews at up to ±0.4V/µs. The output
can swing from zero to full scale. With a 1/4FS to 3/4FS
output transition, the amplifier output typically settles to
1/2LSB in less than 5µs when loaded with 10kΩ in par-
allel with 50pF. The buffer amplifier is stable with any
combination of resistive loads >10kΩ and capacitive
loads <50pF.
Power-On Reset
All registers of the MAX1233/MAX1234 power up at a
default zero state, except the DAC data register, which
is set to 10000000, so the output is at midscale.
Keypad Controller and GPIO
The keypad controller is designed to interface a matrix-
type 4 rows × 4 columns (16 keys or fewer) keypad to a
host controller. The KEY control register controls keypad
interrupt, keypad scan, and keypad debounce times.
The KeyMask and ColumnMask registers enable mask-
ing of a particular key or an entire column of the keypad
when they are not in use. The MAX1233/MAX1234 offer
two keypad data registers. KPData1 holds all keypad
scan results, including masked data, and is thus the
pending register. KPData2 holds keypad scan results of
only the unmasked keys. If 12 or fewer keys are being
monitored, one or more of the row/column pins of the
MAX1233/MAX1234 can be software programmed as
GPIO pins.
Touch-Screen Detection
Touch-screen detection can be enabled or disabled by
writing to the ADC control register as shown in Table 4.
Touch-screen detection is disabled at initial power-up.
Once touch-screen detection is enabled, the Y- driver
is on and the Y- pin is connected to GND. The X+ pin is
Y+
X-
Y-
S2
Figure 6. Touch-Screen Detection Block Diagram
internally pulled to AV_DD through a 1MΩ resistor as
shown in Figure 6. When the screen is touched, the X+
pin is pulled to GND through the touch screen and a
touch is detected.
When the 1MΩ pullup resistor is first connected, the X+
pin can be floating near ground. To prevent false touch
detection in this case, the X+ pin is precharged high for
0.1µs using the 7Ω PMOS driver before touch detection
begins.
Key-Press Detection
Key-press detection can be enabled or disabled by
writing to the keypad control register as shown in Table
17. Key-press detection is disabled at initial power-up.
Once key-press detection is enabled, the C_ pins are
internally connected to DV_DD and the R_ pins are inter-
nally pulled to GND through a 16kΩ resistor. When a
key is pressed, the associated row pin is pulled to
DV_DD and the key press is detected. Figure 7 shows
the key-press detection circuitry.
Interrupts
PEN Interrupt Request (PENIRQ)
The PENIRQ output can be used to alert the host con-
troller of a screen touch. The PENIRQ output is normally
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