MAX1234ETI+T Maxim Integrated Products, MAX1234ETI+T Datasheet - Page 16

• Manufacturer Part Number: MAX1234ETI+T
• Description: IC CNTRLR TOUCH 28-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Resistiver

Specifications of MAX1234ETI+T

• Touch Panel Interface: 4-Wire
• Number Of Inputs/keys: 1, 4 x 4 Keypad
• Resolution (bits): 8, 10, 12 b
• Data Interface: MICROWIRE™, QSPI™, Serial, SPI™
• Data Rate/sampling Rate (sps, Bps): 50k
• Voltage Reference: Internal
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TQFN Exposed Pad
• Applications: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

±15kV ESD-Protected Touch-Screen
Controllers Include DAC and Keypad Controller
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.
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.
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 is the pending reg-
ister. 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 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
internally pulled to AV
Figure 5. DAC Current-Steering Topology
16
SW1
______________________________________________________________________________________
SW2
Keypad Controller and GPIO
SW255
DD
Touch-Screen Detection
through a 1MΩ resistor as
V
REF
Power-On Reset
Output Buffer
OUT
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 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
nally pulled to GND through a 16kΩ resistor. When a
key is pressed, the associated row pin is pulled to
DV
the key-press detection circuitry.
The PENIRQ output can be used to alert the host con-
troller of a screen touch. The PENIRQ output is normally
high and goes low after a screen touch is detected.
Figure 6. Touch-Screen Detection Block Diagram
DD
SCREEN
TOUCH
and the key press is detected. Figure 7 shows
PEN Interrupt Request (PENIRQ)
S2
S1
+AV
X+
Y+
X-
Y-
DD
DD
1MΩ
Key-Press Detection
and the R_ pins are inter-
TOUCH-SCREEN
DETECTOR
Interrupts
PENIRQ